Hot Water Heat Pumps: Choose Your Refrigerant & Brand Wisely!

reclaim heat pump

Having observed countless passionate discussions in various online forums on hot water heat pumps, it’s clear to me that people care – a lot – about this seemingly mundane subject.

The conversations start like this :

  1. Take innocuous hot water question into hand
  2. Remove pin
  3. Lob into open energy forum
  4. Take cover !

Let’s agree that gas hot water belongs in the bin, and thermal storage is a cheap battery for your solar energy. This allows us to explore the basic principle and virtues of the incredibly efficient heat pump hot water service.

It’s The Refrigerant That Makes Things Hot

Counterintuitively, a fluid called refrigerant is crucial in a heat pump hot water system because it acts as the medium that transports heat from the air to the water. The refrigerant absorbs heat from the surrounding air. Even in very cold conditions, the air contains thermal energy that can be harnessed.

Without the refrigerant, there would be no way to capture and move that embodied heat to where it’s needed. It’s counterintuitive because we don’t often think of “cooling” substances as being key players in heating water, but in the case of heat pumps, they’re absolutely vital.

You input one measly kilowatt of power into this magical box with refrigerant flowing through it, and voila – it pumps out 4kW on the other end. This astonishing ratio is the Coefficient Of Performance (COP) and can be greater than 1 (1 equals 100% efficiency) because you are not creating heat but harnessing it.

COP varies depending on several factors, including the model, the type of refrigerant used, the task at hand, and the ambient temperature. Beware though. Manufacturers may get overly optimistic with their ratings, so just as you should be sceptical of an EV’s claimed range, a healthy dose of scepticism is required when reading heat pump specifications.

Beware Of Condensation

When heat is captured outside and pumped inside your house, condensation can become a problem. When trying to suck 20ºC of heat out of the air in winter, which is only 5ºC above zero, moisture can condense on your compressor unit, making it ice solid like an unloved share house freezer. Good heat pumps designed to operate at low temperatures work around this. Ground-sourced heat pumps also solve this but are expensive and thus not popular with us Aussie cheapskates.

Hot Water Needs Higher Temperatures

Every day, you need your hot water storage to exceed 65°C to eliminate bacteria like legionella1. Cheaper heat pumps using R134a or R410a refrigerant can achieve this normally, but when it’s cold, they struggle. Manufacturers actually incorporate a traditional booster element as a safety net, even if it’s less energy efficient.

Better Pumps Use Natural Refrigerants

CO² and R290 (propane) are actually a lot more useful than anyone ever thought. While other refrigerants mentioned have a horrendous Global Warming Potential, literally 1430 or 2080 times worse for the climate than CO² when they escape, good old BBQ gas (propane) ranks as 0.02 GWP. It beggars belief that we’ve been paying the chemical industries for artificial refrigerants for so long.

The best thing about CO² and R290 heat pumps is that they don’t need a booster element. They’ll perform better at lower ambient temperatures and still attain 75 to 90°C  water delivery, enough to run a ring main in a hotel or hospital. They’re a real game changer in hot water.


hot water heat pump install

You can see when someone is proud of their work, and all the pipes are insulated up to standard, not down to price. Kudos to Adelaide Heat Pumps.

Stiebel Eltron, Sanden, Reclaim, iStore

While I’m sure none are flawless, these brands are the ones I’d buy myself. In contrast, the cheap end of the market is littered with junk. Signing over the STC incentives available to get a “free” system is fraught with danger. I was once gifted a Chromagen (solar) hot water unit. After installing that one, you couldn’t pay me to own another.

Insights From A Heat-Pump Insider

Recently my comrade Kim Wainwright wrote a great piece on this that touched on the financial returns of heat pumps; in fact, it touched off 130+ comments. So to further inflame the situation, here’s some inside info from my mate Karl Jensen that might pique your interest. Full disclosure, Karl wholesales iStore units,2 but he’s also a solar industry veteran who regularly offers valuable advice in all kinds of media for free.

Heating capacity of water heaters is rated using specific conditions, like 15°C inlet water temperature and 32°C ambient temperature. Rinnai’s enviroflow uses these numbers to claim a Coefficient of Performance (COP) of 5.6. But these numbers don’t tell the whole story, and the marketing can be misleading.


iStore’s 180L unit can reach a COP of 6.85 at these conditions, but it’s not typical. So, iStore uses a more realistic COP of 4 that’s achievable most of the time. (except during very cold weather or at the very end of the heating cycle)


To truly compare performance, we need to look at Small-scale Technology Certificates (STCs), which each unit earns based on its climate zone.


In Victoria, for example, iStore’s unit gets 25 STCs. This means it will save 25,000kgs of CO2 emissions over 8 years, the duration of the STC scheme. Sanden and Reclaim units get 27 STCs, which translates to an extra 2,000kgs CO2 saved, or 2,000kWh less energy used over the same period. This difference equals 0.68kWh less energy to heat 200 liters of water each day.


If you’re using solar energy that you’d otherwise send to the grid, the cost difference between the Sanden and iStore units is about 3.4 cents per day. But the Sanden unit is typically $2,000 more expensive than iStore’s. So, if you’re using your solar energy, it takes 161 years to recoup the cost difference. And if you’re using grid power at 28c/kWh, it takes almost 20 years.


Remember, these numbers depend on how much water you use. If your household uses double the average amount of water, the energy difference between the units is effectively halved.

iStore heat pump hot water unit installed

A happy iStore customer showing off a good quality plumbing job

Heat Pump PV Diverters?

Resistive hot water heaters use a lot of energy. So getting a sophisticated hot-water PV diverter device to control the heating element can make sense for maximising solar self-consumption. But with good heat pumps using a quarter of the energy, I’d argue that you don’t need anything more than a simple timer to control them. On all but the most horrible solar days, your heat pump’s power draw is likely to fit under the solar curve. The good news is, decent heat pumps come with built in timers.

Choose Your Heat Pump Wisely

If you’re puzzled over the cost implications of different units, you’re not alone. Heating capacity, CO2 emissions, energy consumption, and cost are key in your selection process. Variables like household size, local climate, water usage (dare I say number of daughters?) and whether you’re using solar or grid power can significantly impact economic calculations. In fact, if you like spreadsheets, there’s one here which compares.

The Take Home Message

The bottom line is that heat pumps are more expensive; they have far more moving parts than a standard hot water tank; but use far less electricity. This super efficiency helps lower bills and makes great storage for your solar energy, without needing a plumber on the roof. Heat pumps are quickly killing conventional solar hot water.

Join me next week as I play devil’s advocate, explaining how terrible heat pumps are. Instead, we’ll uncover what I installed for my Mum, the most elegantly simple, durable, heirloom-quality hot water service ever devised.


  1. At least one expert disagrees with this statement
  2. to be crystal clear the iStore heat pump HWS uses a high GWP refrigerant R134a.
About Anthony Bennett

Anthony joined the SolarQuotes team in 2022. He’s a licensed electrician, builder, roofer and solar installer who for 14 years did jobs all over SA - residential, commercial, on-grid and off-grid. A true enthusiast with a skillset the typical solar installer might not have, his blogs are typically deep dives that draw on his decades of experience in the industry to educate and entertain. Read Anthony's full bio.


  1. Spot on!! It’s important to check the refrigerant for residential DHW water.

    Adding to your article, R410a heat pump does not bring the hot water temperature above 56C in winter. So, element always switch on for R410a heat pump.

    R134a is fine for ambient temperature above 5C to deliver 65C hot water. If the ambient temperature drops to 0C, the heat pump will need to cycle the water many times to reach 65C, which consume more electricity power and decrease COP.

    • One thing is often overlooked The cost premium of the heat pump hot water service. A good resistive hot water service is $1,000. A good heat pump is 3500 so for your 2,500 difference what’s going to give you a better return on investment, additional solar or the heat pump? Anybody with a house of two people, the additional solar because you generally produces more power than just consumed by the hot water service. So you’re a net positive. However, about a five person house and you still got a hot water then you return on investment goes the other way and you’re better off with the heat pump

      • This is what I am struggling with. I am building a new house and need a hot water service for the ensuite and main bathrooms. I am on my own (don’t ask why I am building a larger house!) and have a large solar system and a significant excess of solar power. But I will rent the flat out when I am finished the house.

        It seems to me that resistive heaters on a timer would suit me better than heat pumps because my excess solar at 6c kW/h (which will proably decrease over time) would cheaply cover my water heating needs. The main bathroom will probably not get much use except for visitirs. The increased cost of the heat pumps would probably never be recouped. Plus maintence is much more expensive.

        Have I missed something?

        • Geoff Miell says

          Foresooth: – “I am on my own (don’t ask why I am building a larger house!) and have a large solar system and a significant excess of solar power.

          How much excess solar? Would it still be sufficient to support a higher electric current demand from a resistive hot water heater in winter or during periods of low solar irradiance? Or would you need to import electricity from the grid? I’d suggest that increases your operating costs compared with heat pumps systems.

          Foresooth: – “The increased cost of the heat pumps would probably never be recouped.

          I’d suggest that depends on a number of factors/circumstances including:
          * expected lives of the comparative systems;
          * comparative capital costs;
          * comparative operating costs over the lives of the respective systems.

          In my experience, the remarkable energy efficiency of a Sanden heat pump hot water system compared with resistive electric & gas-fired systems is hard to beat, even in freezing winter conditions.

          Foresooth: – “The increased cost of the heat pumps would probably never be recouped.

          I replaced my aging, corroding gas-fired hot water system with a Sanden heat pump system more than 8 years and 4 months ago. I’d suggest the increased capital costs (compared with if I had replaced like-for-like gas, or with an alternative new resistive electric system) have now been fully recouped due to substantially lower operating costs.

          Foresooth: – “Plus maintence is much more expensive.

          What expensive maintenance? So far not in my experience.

          • Geoff – here are some of the circumstances I am making my assessment on.

            I live on the Mid-north coast of NSW near the sea so temps are mild in winter and it is reasonably sunny in an average year. I have 9.2kW of very well sited panels with no shading on a 3 phase Fronius 7kW inverter. My total energy use currently is about125kWh a month, feed-in about 1000kWh so I have plenty to run 2 storage systems. I get 12c kWh for the first 5kWhper day (not sure if it is on all 3 phases, possibly only one) and 6c after that. Base usage will at least double when I rent out the flat, perhaps more.

            So on a back of envelope calculation, comparing two resistive units of say 250 and 315l to two similar heat pump units I am up for $2,000 approx against $7,000. Given resistive units are very, very reliable and I am able to replace thermostats and elements myself cheaply and even my local plumbing supplies shop owner doesn’t recommend heat pump units because of service and repair costs of heat pumps even though he sell s and repairs them, they don’t seem to make financial sense. Unless I am missing something.

            Given airconditioners use the same principles and mechanics and are reasonably cheap and very reliable, why are heat pumps so expensive?

          • David Walsh says

            Hi Foresooth,
            Have you done the comparison against solar hot water? I would be interested to hear the results for heat pump costs from anyone who have had them for 25 + years because solar hot water units just seem to go on and on no issues.

          • Geoff Miell says

            Foresooth: – “So on a back of envelope calculation, comparing two resistive units of say 250 and 315l to two similar heat pump units I am up for $2,000 approx against $7,000.

            That’s only your capital cost comparison – the difference is $5k. Where’s your running cost comparison, Foresooth? You need to estimate your average daily hot water usage and then work out the energy required to heat that amount of water. The resistive hot water heater efficiency is no better than 1, whereas the heat pump water heater is far more energy efficient.

            To give you an idea of how energy efficient, per the test report published by Washington State University in association with Bonneville Power Administration, titled Laboratory Assessment of Sanden GAU Heat Pump Water Heater, dated 18 Sep 2013, for the laboratory assessment of the Sanden model # GAU-A45HPA heat pump water heater (HPWH), Table 3 included:

            Outside Air Temperature _ _ CoP _ _ Output Capacity _ _ Input Power
            17 ºF ( -8.3 ºC) _ _ _ _ _ _ _ 2.1 _ _ _ _ 4.0 kW _ _ _ _ _ _ 1.9 kW
            35 ºF ( 1.7 ºC) _ _ _ _ _ _ _ 2.75 _ _ _ _3.6 kW _ _ _ _ _ _ 1.3 kW
            50 ºF (10.0 ºC) _ _ _ _ _ _ _ 3.7 _ _ _ _ 4.0 kW _ _ _ _ _ _ 1.1 kW
            67 ºF (19.4 ºC) _ _ _ _ _ _ _ 4.2 _ _ _ _ 4.1 kW _ _ _ _ _ _ 0.97 kW
            95 ºF (35.0 ºC) _ _ _ _ _ _ _ 5.0 _ _ _ _ 4.6 kW _ _ _ _ _ _ 0.93 kW

            Foresooth: – “Unless I am missing something.

            Yep, you’re missing the running cost & whole-of-life running cost comparisons. See Kim Wainwright’s post and comparison calculations at:

            See also my comments at:

            Foresooth: – “…why are heat pumps so expensive?

            I’d suggest it’s still a relatively niche market, but I suspect that’s changing.

          • David – I have considered solar hot water which is generally very reliable. However, my roof design does not allow a tank on roof. My roof is made of pre-fabricated metal and foam sandwich panels (for build simplification and insulation reasons) and can take only limited loads. And the cost is still not competitive with a resistance based system. And other design reasons also rule it out for me despite the actual siting being very good.

        • Geoff – did you read the bit about having excess solar and living in a mild temp zone? Currently, I am getting credits of about $50 a month on my electricity bill but my water in the flat is heated by gas. When I finish the house the flat will be rented and I will have significant rent return which will include payment for energy costs, more than offsetting the reduced solar credit. And I will probably change the flat water heater to resistive electricity.

          Given the capital cost difference (ignoring the flat) of at least $5,000(probably a lot more as I don’t think I will be eligible for subsidies as I am not replacing units but building new) plus the widely known likely maintenance costs and probably shorter lifespan of a heat pump, I cannot see any way it can be competitive. As stated in the article I am a low heating user in a mild climate with large excess solar so the payback can spin out to 30-40 years. And during that time I would most likely have to replace both units at least once making the payback much longer again.

          For me heat pumps would only make financial sense if their cost was close to a resistive unit’s and their reliability was better.

          • Geoff Miell says

            Foresooth: – “Geoff – did you read the bit about having excess solar and living in a mild temp zone?

            Yep. So I’d expect it to be a rare occurrence to see ambient air temperatures in your neck-of-the-woods at or below +10 ºC? I’d suggest then that a heat pump system would require no more than a quarter of the energy on average in winter (and even less in summer) to heat your hot water compared with a resistive system. You would have more solar available to power other energy-intensive appliances, like air-con, battery energy storage, EVs, for now or planned in future.

            I’d suggest being in a milder climate means your payback period for a heat pump (compared with resistive) system would likely be shorter compared with my actual experience in a colder climate. I’d suggest your solar credits would likely be significantly higher with a heat pump.

            Foresooth: – “…my water in the flat is heated by gas.

            What makes you think gas will remain affordable and abundant for your tenant?

            And ICYMI, the NSW Climate Change (Net Zero Future) Bill 2023 was assented on Mon 11 Dec 2023 – Act No 48 of 2023.

            Expect gas for domestic residences to be phased out in future.

            Foresooth: – “Given the capital cost difference (ignoring the flat) of at least $5,000(probably a lot more as I don’t think I will be eligible for subsidies as I am not replacing units but building new) plus the widely known likely maintenance costs…

            It seems to me you are attempting to justify something you have already committed to.

            FYI, NSW subsidies:

            Again, what “expensive maintenance”?

          • “plus the widely known likely maintenance costs and probably shorter lifespan of a heat pump”

            Q1. What is this maintenance cost you keep referring to? Please provide factual evidence.

            I think you are referring to the anode on a non stainless steel tank which needs to be inspected and/or replaced (if necessary) every few years.
            This is a common maintenance task with resistive element or gas fuelled HWS as well.

            Likewise, for the PTR valve which also require maintenance on all HWS tanks.

            Q2. Heat pump HWS having shorter life spans???

            Once again, if you wish to be taken seriously at all, then please kindly furnish objective evidence for such a preposterous claim.

            Please note that heat pump technology has been around for a long time.
            Your refrigerator uses one. As does your reverse cycle inverter air conditioners, and your energy efficient electric clothers dryer just to name a few appliances that rely on heat pumps.

            We are all here to get to the truth – “not the sale”.

          • Geoff – you still don’t get it!

            Even at 1/4 of the energy use of a resistive heater, which is highly unlikely as I will have my systems on timers to not draw at the same time, the cost comparison still fails for heat pumps. I won’t have many other high draw demands – just occasional oven use and very occasional aircon as the house is very well insulated. At a loss of 6c a kilowatt hour for feed in, powering the resistive water heaters will cost a very small amount. And then there’s the opportunity cost of the up to $10k greater capital cost to account for.

            The vast difference in price for two resistive units vs two heat pumps simply means it doesn’t make sense to go for the latter. And this is even without the potential for costly maintenance even on quality brand units as documented on this site, on various other sites and according to my well trusted local supplier.

            Also, in NSW as I thought subsidies are only paid when replacing an existing water heater, which I am not. I checked using your reference so thanks for providing that.

  2. Please don’t forget the possible cost of upgrading the house power board to accomodate the heat pump.

    • Don’t you mean downgrade?
      We’re reducing load here.
      A standard kettle draws more than twice as much as a typical heat pump.

    • If the HPHW system is installed where the replaced resistive element HWS was, there should already be a at least 15A wiring present. The HPHW systems I’ve seen use a standard 10A Australian/NZ plug. They draw far less amperage than the old resitive units.

    • The amount of power use by the heat pump is like a small split system 4amp is no much
      No need for board upgrade in a modern home.I am a qualified fridgy.

  3. Thank you, an informative article.

  4. Heat pump HWS are not really “cheap” thermal batteries. At least not in WA where there are no subsidies. Both sanden and reclaim are $6,250 plus $300 for the wifi controller.
    Actual home batteries are becoming cheaper (tesla PW2 now around $13k installed) while thermal batteries (HPHWS) are becoming much more expensive in WA. The sanden / reclaim systems have increased about $1000 in the last year.

  5. Just a correction – the refrigerant is CO₂ not CO².

    Will be interested to see the cons.

    They don’t all apply to each scenario but I can see them fall into one of the following:
    – upfront costs are way higher and this is a barrier for many
    – financial viability if hot water consumption is low/intermittent
    – physical installation constraints
    – noise from the compressor
    – complexity and associated longevity considerations
    – lack of trained/experienced service personnel, especially in regional locations
    – inadequate user controls for automatically selecting cheapest available power be it solar PV or off-peak tariffs
    – insufficient track record for warranty and service support
    – poor / short warranties

    With the cheap / “free” heat pump water heaters being installed using state govt incentive schemes, we are also dealing with “crap heat pump” instals in the same way we have seen “crap solar PV” instals.

    One of the issues with water heaters is apart from new builds they are rarely a planned purchased. Typically the existing water heater unit fails and repair is considered too costly for the age/condition of the unit or too time consuming, so people often just go with a “like for like” replacement because it’s simplest to instal, they can get their hot water back that day and it’s typically cheaper just to get it done. Not everyone has $3-5k sitting there just in case they need a new water heater.

    I looked at it when I replaced our water heater a few years ago but the costs of quality heat pump water heaters were insane and not justifiable. Water heating only costs us $90-130/year (depends on FIT) with a resistive element water heater (last one was 30 years old), so a heat pump water heater just can’t achieve enough savings to make the extra costs worth while.

    • Hi Alex,

      You make a good list of things for potential purchasers to bear in mind but I don’t think your numbers add up.

      A friend in NSW recently went through the subsidised scheme and had a choice between free installation of a cheap unproven brand or a top of the line heat pump from a reputable company for $2000. He went with the second. Going by this page it looks like at the new electricity prices he’ll be saving around $800 per year if his household of 4 pays similar prices and uses average amounts of hot water.

      It’s worth noting that both options had a long warranty, so now would it be crazy for someone who needs to replace an old or failing water heater to go with the cheap option, as they’d be risking $0.

      • Hi Guy, just a note on your claimed saving of $800 a year using a heat pump.
        The average off peak quarterly bill for a household of 4 to 5 is approximately $90 to $120 whether using off peak 1 or 2.
        That amounts to less than $500 per year.
        Also, repair and maintenance costs, not to mention the availability of ” experienced ” repair technicians for heat pumps is an issue to be considered.
        As for the ” board downgrades” that were touted, so tongue in cheek.
        Regulations today are for either rcd protection and isolators at the tank in most states.
        What needs to be considered is the cost of installing an rcbo and timer, and I’ve personally seen alot of incorrect installations of these 2 very simple board upgrades, which can be reasonably costly.

        • Hi Matt. I’ll ask my friend what his actual savings are, but he said they were huge. I realise the link I used was for prices in Victoria, but it is updated and puts the annual cost at $1,100 peak and $900 off peak at average consumption for a 4 person household, vs. $215 to $355 for heat pumps.

          Maybe the economics are not always as good as I suggested but they are generally excellent for large households. There are some hassle factors, but I thought the warranties were at least 5 years.

      • When I changed our water heater at the time if I could have installed a good quality heat pump unit for $2k I would have. But alas the quotes were minimum of $3.5k *more* than a standard resistive element stainless steel 315 litre water heater.

        Considering our water heating only costs circa $100/year to run then saving $70/year for an outlay of $3.5k made zero sense.

        So definitely if you can get quality unit for not much more than a resistive element then the heat pump is a no brainer.

        The more hot water a home consumes the more a heat pump with a large tank makes sense.

      • HP hwu’s are great in principle for small to mid sized units.
        If cost is your main driver look at warranties and total lifecycle costs including replacement costs then make up your mind.

        My last resistive elec hws lasted 17 years and based on heat pump warranties reckoned I would have gone through 3-4 HP units. Not sure if I would have been able to get the subsidised replacements or had to pay full price.

  6. In this age of automation and control, why can’t a simple remote on/off be available for heat pumps? Not 4G , not proprietary apps, just a couple of wires.
    Yes the HP fits in a solar curve but that ignores your other appliances or other needs. A timer is fine if you don’t have anything else you solar shift (car charging, pool pump, dishwasher,home heating etc).
    With Home Assistant I can intelligently decide priorities and maximise self consumption except for a heat pump hws.
    I’m in an cool climate. Some HPs run continuously below 7C to prevent freezing, for me that could months on a peak tariff but no details i can find on consumption. Others use a resistance elements and I’d guess a circulation pump.
    I’d love enough information to make an informed decision and I’d like the same control that is available with resistance HWS.
    Looking forward to your next article.

    • Anthony Bennett says

      Hi Greg,

      I know for sure that Reclaim have some dry contacts in the controller so you can indeed switch the unit on and off using a solar yield signal. I imagine others offer something similar but I haven’t read all the manuals on all the models yet. Let us know if you find any.


    • Andrew Heard says

      Our Sanden uses < 1W when the temp (on in winter) gets low overnight, in Hobart. It only uses ~1kW, so I have the in-built timer set to heat between midday & 1pm, so 1kWh/day, which has always been more than sufficient for a couple. In 2021 when I last crunched the numbers, we had 320 days sufficiently sunny with a 5kW (nominal) PV system (poorly orientated) to completely heat the water from PV, on the TOU tariff of $0.15/kWh, which was about $7 of actual cost for the year.

  7. Re Istore refrigerant. Cannot find anywhere what it uses, including on the spreadsheet referred to.

  8. I have had a Sanden heat pump for 3 years. No performance problems and I am confident this is a reliable machine. I justified the extra cost of a sanden based on a friend recommendation and mostly because of the CO2 compressor and the suitability for icey Canberra where I live, as well as the large stainless steel tank.
    Two issues I have with it though are:
    1. its difficult to access control settings. Sort of glad they keep it simple and thus reliable, but have to screw off the side cover to change the times. Although I haven’t needed to access and change anything it in over a year now.
    2. It’s antifreeze protection is dumb. When the temp sensor bulb on the outdoor coil (evaporator) reads below zero (or whatever sanden factory has set), it will run a full tank heating cycle, not just a short circulation intermittently to keep the water pipes from icing (as my hydronic underfloor heat pump does). On many a Canberra frosty morning, the Sanden will start at about 3 or 4 am and run for 2 or 3 hrs to heat my tank for the day, even though I have it set to a block out to only run between 11 am a 3 pm, which is when solar PV and ambient temp is max. Of course the COP is bad when it’s freezing outside and the outdoor coil freezes up frequently and needs to go through regular defrosts. I contacted tech support but they couldn’t appreciate my suggestion that the antifreeze control only needs to circulate storage tank water through the water pipes for a few minutes every 30 or so minutes. The instruction manual references an antifreeze heating coil to wrap around the outside water pipes, but that wasn’t suggested by tech support, nor do I see how it overrides the dumb antifreeze protection control.
    That said, this only occurs maybe 20 mornings each winter, so not a big loss. But I have to call out the dumb antifreeze control.

  9. Alexander Newman says

    Bother! We recently got a Rheem Ambiheat HDc270 via the builder via the plumber as that was what they supplied. A quick view of the specs shows the refrigerant to be R134a @$*#$!!#@. Oh well. It hasn’t been installed yet, and is still in its crate. I’ll try and see if it can be returned…but I won’t be holding my breath.

    • Alexander Newman says

      We decided not to argue and got the Rheem installed. Seems fine so far – hot water all day long, fed by the PV array when functioning. Please ignore the previous squawking and clucking. Cheers, AlexN.

  10. Need to updated Hydrotherm in the excel file, it’s propane refrigerant and 260 liters. Also has a booster.

    • Anthony Bennett says

      Hi Denis,

      The spreadsheet is a collaborative effort organised through My Efficient Electric Home on Facebook. If you have a look there they may be able to make adjustments

      • Tim Chirgwin says

        Hi Anthony,

        I took your advice, made a change to the price of electricity on the spreadsheet you recommend, (by members of an energy enthusiast group who fortunately have some very good other advice)

        Astute buyers with solar (who have taken SQ advice to fill up their roof with solar panels) can utilise the Solar FIT price of 6c /kwh instead of the 27c in the sheet, and so the payback on the purchase of Heat Pumps is given at between 14 and 24 years. Ouch!

        An environmental warrior, or one that loves cold showers, or the frugal and retired, who use only 5 kwh of resistive water heating power will take 28 to 48 years to make a payback. 2x Ouch!

        With warranties of only 6 years or less on most heat pumps, one would expect many replacements before this time has expired and so significant higher capital replacement costs will be burnt into the hip pocket nerve of those people who have allowed themselves to be blindsided by energy efficiency rather than cost efficiency.

        Of course those who are concerned about manufacturing energy cost, wastage of resources and disposal costs and landfill space will probably also know also that exactly the same cost of free sun energy is used in both of the the systems being compared when run on sun.

        Those without solar energy capture will have to work out their own costs and returns which could favour buying a heat pump,.. or maybe not if they are frugal hot water users, especially if they already have recently had a resistive HWS installed..

  11. Craig Duncan says

    We had one of these because of basix requirements. It failed a number of times from new. To use a refrigeration unit to produce hot water is such a ridiculous idea they are full of unreliable electronics. They shut off if outside temperature gets near zero degrees c. The technician who I came to know quite well told me they are a failed tech but the companies get government kick backs.
    I would say to the service technician “all I want to do is boil water it shouldn’t be rocket science”
    In the end after 18 months and still under warranty dozens of break downs I disconnected it and took it to the tip! I bought a 500 litre duel element. It was luxury to be able to have a hot shower again!

    • Anthony Bennett says

      Hi Craig,

      Tune in for the next episode of “heat pumps are a deeply held idea” because you’re not the only customer I know who’s had issues. There’s no magic bullet but the advantage you have with a dual element machine is that you can have a smaller one in the bottom hooked up to a solar diverter, such as catchpower, ohmpilot or an inverter yield driven switch.

      • Tim Chirgwin says

        That is really thinking for positive gain,
        Remember to include the savings in purchase price of the cheap reliable resistive HWS with a diverter or solar yield relay and consider the extra savings over those heat pumps that have a comparable warranty period, and ability to work in cold climates without resistive back up, and has cheap maintenance costs that are comparable for the times outside of warranty to match typical good resistive HWS lifespans.
        We need to compare all costs and benefits over the full life in normal household use and this will take you more effort,… include the benefit of short HW run lengths (time savings) and hot water wastage.(power and water savings), and that heaters installed inside reduce heating costs of the house, and less standing losses than those HWS that must be out side is also significant.

        The savings in purchase price of the resistive HWS can be used to purchase extra PV panels, and the benefit of having extra solar on your roof to reduce your early and late but expensive peak power (think 55c/kWh) is a significant benefit while your water heating can be load shifted to use solar surplus which generates a 6c FIT.

        While many good heat pumps boast a Coefficient Of Power (COP of 4) (energy saving 4x) compared to a resistive HWS, the extra panels paid for by the saving in capital cost has a benefit of the COST OF POWER that is 9 times the benefit., when you reduce peak usage.

        You could go for a roof full of solar and a heat pump if you don’t care that your home loan could have been paid off sooner if you were smart on cost savings rather than energy savings.

        Of course some will say they seek energy savings so will fit complex and expensive machines with shorter lifecycles when simple and long lasting ones will do the job more cost effectively, and with less landfill.

        Many well intentioned people are blindsided by energy efficiency instead of cost efficiency,..when the suns energy for both HWS can be FREE.

    • John Peters says

      What “500 litre duel element” HWS did you buy ?

  12. koen weijand says

    One thing that bothers me in heat pumps is that they cannot be steered to control the input power they absorb. Temperature is about the only measure of control. EV´s can be controlled in how much power they take while charging , and that feature is used by smart charging stations to charge on PV excess power only. Same should be possible with heatpumps.

    • Anthony Bennett says

      Hi Koen,

      I suspect you’re right, in that large “inverter” air conditioners run variable speed compressors to make them most efficient, whereas old units just used to cycle on and off. However the extra layer of power handling electronics would also add expense and when my little Quantum unit only uses 800w to begin with it might be a case of diminishing returns. Perhaps that’s the next level of refinement for heat pumps of the future?


    • There are units that do exactly that. They run on DC and will match your production profile. The downside, you need dedicated solar panels to supply the dc. So once the water is hot, PV is wasted.
      Inverter air conditioners convert AC to DC then back to AC to run the compressor but change the frequency of the AC to control the speed.
      They do that based on temperature. Doesn’t seem a big step to link that to available Solar to me.

      • Tim Chirgwin says

        It is a very good idea to use the dc panels that are dedicated to the hot water only, and while it appears wasteful it is only very slight in reality.

        A huge bonus can be achieved when the energy distributor will not allow more PV to be connected to the grid, forcing us to purchase power at high rates, but we can partial offgrid without batteries and the bottom element can be set up with extra dc panels and cover 100% of the expected load for the most typical days, leaving only a small amount to either be topped up from the grid during inclement weather or “wasted on very good solar days.
        Way too often we look at worst case situations and think that it is typical when the average is often far different.

        With solar panels so cheap and purchased electricity so expensive, who cares if some sunshine got “wasted”, cos if we didn’t put up the panels then all of it got “wasted”.

  13. I had a Reclaim Energy CO2 heat pump installed 4 weeks ago in Adelaide. So far its working fine. It heats to 59-60C not the 65C mentioned in the article, but the Reclaim information seems to suggest that this is sufficient to protect against Legionella.
    Please note that the installer keeps telling me that the system cannot be connected to my controlled load power, due to how TOU tariffs work in SA.
    Therefore, I am currently connected to standard daytime tariff until I can get solar PV installed. I still don’t understand this, as AGL has told me that I can still utilise controlled load on TOU.
    Also,the installer was the same one as featured in the article as being proud of their work. However, after 4 weeks I am still waiting for a replacement of the tank which was damaged in transit. The first one was damaged and this was meant to be the replacement, but was also damaged.As it was getting late in the day,I had to install the damaged tank so that I had hot water, on the promise that a new tank would take “a couple of days” to be ordered. Still waiting. Still chasing! Moral of the story is “Don’t pay the invoice until the job is complete”. I made the mistake in paying in good faith, on the promise of a replacement tank. Silly me.
    I also contacted Reclaim Energy directly who made all the right noises, but in the end just asked the installer to contact me, and did nothing else.
    Furthermore, be careful of another Reclaim installer (which also installs solar in Adelaide western suburbs) as they quoted a ridiculous price of $8500 to replace my old thermosiphon system with a heat pump.
    Happy with the heat pump. Not happy with complete lack of service and communication.

    • Anthony Bennett says

      Hi Rob,

      Unusual that you should have poor service, I suspect they’re pretty busy, but I trust the water is hot, which is the main thing. Let us know how you get on.


      • Hi Anthony.
        Just got a call this morning from installer. New HW tanks have finally arrived and replacement booked for next Monday. Apparently there has been a spate of units damaged in transit,and Reclaim Energy has now changed their transport company. My post yesterday must have put “the vibe” out there.

  14. Thanks Anthony.
    The installer keeps telling me that they are awaiting delivery of stock. I don’t understand how they can continue operating if it takes so long to receive their stock.
    On the subject of noise raised by Alex above, I can confirm that the Reclaim CO2 heat pump is very quiet. It is rated at 37dB, and runs at a very gentle hum You can barely hear it operating.

  15. Interesting article! I’m using a $700. lpg instantaneous hot water heater, and because I don’t use much hot water I get 6-12 months out of one gas bottle. That’s around $135+40 rental . The 12 months is only obtainable if I don’t shower everyday, and I don’t for most of the year because my fave online doctor says that it’s beneficial to only shower every 3-4 days so as to not wash off our skins natural oil coating. I also use the lpg to cook meals about every third evening. I don’t see how a forking out cash for a new politically correct water heater can even come close to this cheap and reliable form of heating, I don’t think that I will live long enough to see breakeven on an expensive heat pump setup, but try to change my mind if you have some info that I’m not aware of!

  16. “Every day, you need your hot water storage to exceed 65°C to eliminate bacteria like legionella.”

    It was very honourable of you to include the footnote Anthony. I’m also chiming in to question that statement.

    IMO the idea of keeping ALL water temperatures over 60°C is overreaction to a minuscule risk – and why in the US it’s not mandated by authorities.

    Legionella thrives a few degrees either side of 35°C and can slowly grow or survive at temperatures in the 40’s. It dies off over time in the 50’s. 60+°C is bactericidal in under an hour, but colonies of legionella can survive short blasts of 60+°C.

    I can understand the WHO recommending 60+°C because their job is only to minimise health risks but IRL legionella rarely builds up in working hot water systems above 45°C. Town water supplies are already treated to reduce it and healthy people can tolerate modest amounts of it.

    That does not mean there’s no risk but it’s one that mainly affects immunocompromised people over 50 and can be managed. The most important thing is not the water heater unless it’s rarely used, but to avoid/clear all pipes that collect stagnant water. I personally wouldn’t put a water heater lower than 45°C, but build up is doubly unlikely if you use up stored water around daily, (and triply if you don’t shower with your mouth open 😉

    I have our water set above 60°C for unrelated reasons (getting enough for our household out of a small tank). The caveat is that if I go back under 50°C I’d throw in high temperature days, e.g. once a month before heavy use put it on 70°C for a couple of hours to kill it all with a good margin for error (some parts of the water tank may be cooler than the setting).

    Just a personal view of course. I mention it because there are environmental costs for keeping water well above temperatures needed for use and some here may be interested in that and managing their own risk.

  17. Our Sanden has performed flawlessly & saved thousands after replacing the LPgas continuous HWS.
    It’s timed to run while the sun is high in the sky & Solar PV is maxing out.

    We also recently installed a 160 litre Reclaim Energy for our Airbnb & also perfect, but better than Sanden given it’s better timer controls.

    Both CO2, & stainless tanks for 15 yr warranty.

    BTW, the Apricus is another HP that uses R290 gas, so also Ultra low GWP combined with high efficiency & modest price.

  18. Andrew Heard says

    Our 250L GAU-A45HPC Sanden uses < 1W when the temp (on in winter) gets low overnight, in Hobart. It doesn't go below zero, or even close, as in ACT. It only uses ~1kW, so I have the in-built (block out) timer set to heat between midday & 1pm, so about 1kWh/day, which has always been more than sufficient for a water-wise couple. In 2021 when I last crunched the numbers, we had about 320 days sufficiently sunny with a 5kW (nominal) PV system (poorly orientated) to completely heat the water from PV, on the TOU tariff of $0.15/kWh, which was about $7 of actual cost for the year. Some of my experience here

    • Geoff Miell says

      Andrew Heard,
      Our 250L GAU-A45HPC Sanden uses < 1W when the temp (on in winter) gets low overnight, in Hobart.

      I’d suggest not – the specification for Sanden GAU-A45HPC includes (bold text my emphasis):

      Heat Output (at 32.45 ºC ambient / 18.74 ºC cold water inlet): _ _ 4.99 kW
      Electric Input (at 32.45 ºC ambient / 18.74 ºC cold water inlet): _ _0.84 kW
      COP (at 32.45 ºC ambient / 18.74 ºC cold water inlet): _ _ _ _ _ _ 5.96^
      Refrigerant: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ CO₂ (R744)
      Water Temperature Setting (Nominal) – from Heat Pump unit: _ _63 ºC

      Ambient Air Operating Temperature: _ _ _ _ _ _ _ _ _ _ _ -10 ºC to +42 ºC
      Maximum Operating Water Pressure: _ _ _ _ _ _ _ _ _ _ _ _ _ _850 kPa
      Maximum Heat Output: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _6.0 kW
      Maximum Rated Power Input: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _2.3 kW

      I’d suggest the maximum power input of 2.3 kW is at -10 ºC ambient air temperature.

      A Washington State University in association with Bonneville Power Administration published a test report titled Laboratory Assessment of Sanden GAU Heat Pump Water Heater, dated 18 Sep 2013, concerning a laboratory assessment of the Sanden model # GAU-A45HPA heat pump water heater (HPWH). Table 3 provided CoPs, Output Capacity & Input Power for a range of ambient air temperatures between 17 °F (-8.3 °C) to 95°F (35 °C). Table 3 indicates that the Input Power increases as ambient air temperature decreases in order to maintain the Output Capacity at about 4 kW.

  19. A good start to help me make a decision about which to choose when my gas instant hot water finally goes to god..:-)
    It would be good to see some guidance on siting of the new units to maximise efficiency of the unit. For example how much difference does placing the unit on the north facing wall of the house make? I often wonder if actually placing the AC unit within the roof space would make a difference after all it’s like a furnace up there in summer and a lot warmer in winter.
    Still wonder why we don’t just use the old solarhart rooftop units as an alternative… what would be great is a full comparison spreadsheet that includes PV diverter technology, solar siphon and the heat pump options in one document.

  20. Thought I would chime in with my good experience so far – hope this doesn’t hex it.
    Got a quote to replace old solar/electric system – was $1.5k more then for a reclaim heat pump.
    Local plumber wasn’t a big fan – said he’d had noise complaints.
    Anyway went with Reclaim as my workplace has installed them as well and availability was great – next day as opposed to 6 week wait for solar.
    The last bill is about 20% down even with the energy price increases.
    I also have a friend who has installed a cheaper brand- chromagen I think- and he is very happy 2 years no problems.

  21. Ross Falcke says

    A little off track but still relative.

    We have gas hydronic heating with panels. Been told heat pumps won’t get the water hot enough to use for heating. Any truth in that?

    Also have solar assisted gas instant hot water. How does this stack up cost wise compared to jut the heat pump?


    • Anthony Bennett says

      Hi Roscoe,

      Heat pumps certainly will get hot enough for hydronic floor heating and hydronic panels, I have seen them myself here in Australia.

      Gas assisted solar hot water is also a good option, but it’s a couple layers of complexity and when the solar side of the system fails for whatever reason, nobody notices because the gas booster just takes over all the work instead of just some of it. It’s worth checking that the tank is warm on a sunny day.

    • Geoff Miell says

      Ross Falcke,
      Been told heat pumps won’t get the water hot enough to use for heating. Any truth in that?

      Domestic heat pump water heaters, like the Sanden Eco® Plus model GAU-A45HPC, and Reclaim Energy model EHPE-4550P-A, deliver hot water at 63 ºC.

      Industrial high temperature (i.e. 100+ ºC) heat pumps are commercially available to achieve up to 165 ºC (e.g. KOBELCO SGH 165) for heating processes such as drying, sterilization, distillation and concentration.

      See the YouTube video published by the Australian Alliance for Energy Productivity on 27 Feb 2023, titled 2023 High-temperature Heat Pumps Update with Dr Cordin Arpagaus – 22 February 2023, duration 1:02:53.

    • Geoff Miell says

      Ross Falcke,
      Also have solar assisted gas instant hot water. How does this stack up cost wise compared to jut the heat pump?

      Domestic gas production in Australia is in decline. I’d suggest gas prices will continue to rise.

      A quick look at the AEMO’s Gas Statement of Opportunities – March 2023 shows in Figure 26 Reserves and resources reported in the 2022 GSOO and 2023 GSOO (on page 51):

      * 2P developed reserves: _ 16,659 PJ _ _ R/P: 8.5 years
      * 2P undeveloped reserves: 17,000 PJ _ _ R/P: 8.7 years
      * 2C resources: _ _ _ _ _ _ _41,938 PJ
      as at 31 Dec 2022

      * 2022 actual consumption: _ 1,950 PJ

      The 2P reserves estimate reflects statistically that there should be at least a 50% probability that the quantities actually recovered will equal or exceed the sum of estimated proved plus probable reserves.

      The executive summary of the publication begins with the line “Despite increased production commitments from the gas industry since the 2022 GSOO, gas supply in southern Australia is declining faster than projected demand“.

      It seems the Victorian Government is beginning to heed the warnings, by announcing on Jul 28 that gas connections in new homes will be banned from next year.

      On Jul 31, the NSW Premier Chris Minns told Ben Fordham on-air at Radio 2GB that he is “not pursuing” a ban on gas.

      Where does Chris Minns think NSW’s adequate gas supply is coming from beyond this decade?

  22. David Walsh says

    We have a Reclaim system V2. We are using 2 X 315 Lt existing tanks with the one heat pump and temperature sensor at bottom of second tank. Supplying hot water to up to 10 persons, sometimes some are showering twice per day. We are in a cold sub-alpine area. System went fully operational end of June 2023 so we have had a full month of the coldest weather. My preliminary assessment is that we are getting hotter water for everyone at lower cost. However there a few things I have noticed. According to Reclaim the HP always delivers water at 63 degrees and pump throughput is 110 Lt per hour. I suspect that one or both of these statements are not always true. On a day when no one used any hot water between 7 am and 7 pm and the HP ran from 10 am to 11 pm (programmed times) and the ambient temperature at 10 am was 9 degrees and the temperature during the day hardly got above 12 degrees the sensored temperature did not get above 45 degrees. So in theory in the 9 hours from 10 am to 7 pm the unit should have delivered 990 Lt of 63 degree water to the tanks cycling the water through one and a half times before people returned home and started using water. This suggests that either it is not raising the water temperature passing through the HP by the 20 degrees needed to get it up to 63 degrees ( Therefore it would take two passes needing about 12 hours to get the whole 630 Lt to 60 degrees. Alternatively it is delivering 63 degree hot water back to the tank when the outside weather is cold but at much less than 110 Lt per hour. The fact that on warmer days when the temperature is over 15 degrees the whole tank is getting to 59 degrees on 6 hours seems to confirm that performance is affected by ambient temperature and either the 63 degrees or Lt per hour or both are degraded not just Kw used.

  23. David Walsh says

    Further to my previous post about our Reclaim V2. As other contributors mentioned I also have noticed an opportunity to improve the anti-frost system. During July I noticed that when the ambient temperature dropped below 2 degrees the anti-frost system came on. This was between 2am and 6am. The app says that it is Legionella cycle but I believe that it is the anti-frost. Reclaim says that the anti-frost is programmed to come on until the whole tank registers 59 degrees. However fortunately this seems to be incorrect. It seems to be 3 hours or 59 degrees which ever comes first. This is fortunate because as you will see from my previous post on very cold days it will not even get to 50 degrees especially if people start using hot water. I agree that this seems to be a design fault. 2am is a really inefficient time to start running the HP continuously. I agree with others that it should only come on intermittently to prevent freezing. Even in sub-alpine in Australia you do not get water freezing, you have to go full alpine like ski resorts. It would make sense to change the anti-freeze programming.

  24. One other consideration with regard to refigerant that is worth considering is whether the heat pump will need de-gassing at end of life. As the article mentions, some are not good for the environment and further to the article, legally they cannot be intentionally released. This can add to the cost of proper disposal of the heat pump at end of life.

  25. Bob Gitsham says

    G’day Anthony, I have a hydronic system heating my whole house. The systrem is basically a 300L tank that has 4 different sources of heat input.
    1. wood burning stove with water jacket.
    2. solar hot water panels.
    3. Rinai 16 gas contiuous heater.
    4. there is also a 1500w off peak element, but it is burnt out.

    The whole thing works very well, the main source of heat input is the wood burner, but as I get older I find that cutting firewood is becoming more difficult. As a result I’m using the gas burner more often, while it works well it’s becominbg more expensive to run, and as its nearly 20 years old, I expect it will need replacing some time soon.

    I’m interested in replacing it with heat pump system, I have treid contacting some of the manufacturers, but they, so far have not been very helpful, one who claims to be using propane as the refrigerant giving 65c hot water, which would be ideal, refuses to quote on the basis that as it is an existing hydronic system they would not be able to warranty their unit. I suspect it is because I do not want to buy a whole new sysytem, just the heat pump. Can you offer any advice, and recommend any suppliers.

    • Anthony Bennett says

      Hi Bob,

      Sounds like a fun system. Heat pumps certainly will work but I don’t have a state by state guide for plumbers sorry. Siddons used to offer a “bolt on” heat pump but they’re no longer available. You might try Earthworker in Gippsland and see who they recommend. Or maybe some of the stove companies like Pivot, who often do wetbacks & unconventional stuff like that.


  26. Andrew Heard says

    Thanks Geoff. Maybe I have the model # wrong, maybe its GS3-45HPA-AU? The model I quoted is for the owners & installation manuals. I definitely have my figures correct (eg. 1kWh/d) as the electrical circuit power is continually logged to a database.

    • Geoff Miell says

      Andrew Heard,
      Maybe I have the model # wrong, maybe its GS3-45HPA-AU?

      It’s easy enough to tell. Look at the rating plate on the rear face of the outdoor unit, near the water inlet & outlet recirculation pipes.

      The Sanden model # GAU-A45HPA has a 4-digit LED status display unit hidden under the top metal cover (remove 2 screws each end before lifting off the cover). It was superseded by the more recent model Sanden GAU-A45HPC, I think in Australia around 2017.

      The Sanden GAU-A45HPC has the 4-digit LED status display visible through a window in the side of the metal case of the outdoor unit, above the water inlet & outlet ports.

      I definitely have my figures correct (eg. 1kWh/d) as the electrical circuit power is continually logged to a database.

      Do you record/log ambient air temperatures near the outdoor unit, that correlates with your electrical data? Would you get below freezing temperatures during the middle of the day, when your system is recharging the tank?

      I only get freezing air temperatures overnight through to about 9am worst case. During the day, when the system begins recharging the tank, the ambient air temperature is always above freezing (0 ºC), as far as I can recall.

      • Andrew Heard says

        Geoff – thanks – as per my original post, the model *IS* the GAU-A45HPC, installed 2019, and uses 1kWh/d by virtue of the 23h block-out. In the link to my post I showed a photo of the 4-digit LED with details for setting the block-out time – clearly not intended to be done by a home owner, although our plumber showed no interest in setting it for us. At present I record general ambient temperature but don’t log the temperature near the cylinder (or the water) although I intend to. As I already mentioned Hobart’s minimum temperature is rarely close to freezing. On most days when not heating, the standby power is ~300mW. Below maybe 10C (or it’s a more complex decision & includes a minimum time period) it increases to 5W, not 1W as I originally stated (sorry). For example on the previous night, minimum 6C, the power was 5W between 8pm & 11am. Most of year the standby is 300mW, not 5W.

        • Geoff Miell says

          Andrew Heard,
          As I already mentioned Hobart’s minimum temperature is rarely close to freezing.

          So your Sanden GAU-A45HPC doesn’t activate ‘freeze protection mode’ (regardless of any block-out time settings) at all?

          Per Sanden FAQ:

          Please note that in cold climate regions, the Heat Pump unit will run during the night when the ambient temperature drops below 3ºC. If used in an off-grid system, please ensure that adequate power is available.

          Mine does – Lithgow experiences multiple below freezing minimum temperatures during the winter season. So the ‘freeze protection mode’ engages to heat the system and top-up the tank. It may run briefly a few times overnight. I think the threshold is when the outdoor unit’s water inlet sensor measures below 3 ºC.

          Below maybe 10C (or it’s a more complex decision & includes a minimum time period) it increases to 5W, not 1W as I originally stated (sorry).

          Thanks for confirming standby power consumption. What is the power consumption of your system when the compressor, fan and water recirculation pump are running?

          Per the test report published by Washington State University in association with Bonneville Power Administration, titled Laboratory Assessment of Sanden GAU Heat Pump Water Heater, dated 18 Sep 2013, for the laboratory assessment of the Sanden model # GAU-A45HPA heat pump water heater (HPWH), Table 3 included:

          Outside Air Temperature _ _ CoP _ _ Output Capacity _ _ Input Power
          17 ºF (-8.3 ºC) _ _ _ _ _ _ _ _2.1 _ _ _ _ 4.0 kW _ _ _ _ _ _ 1.9 kW
          35 ºF (1.7 ºC) _ _ _ _ _ _ _ _ 2.75 _ _ _ _3.6 kW _ _ _ _ _ _ 1.3 kW
          50 ºF (10.0 ºC) _ _ _ _ _ _ _ 3.7 _ _ _ _ _4.0 kW _ _ _ _ _ _ 1.1 kW
          67 ºF (19.4 ºC) _ _ _ _ _ _ _ 4.2 _ _ _ _ _4.1 kW _ _ _ _ _ _ 0.97 kW
          95 ºF (35.0 ºC) …

          Are you seeing similar or better Input Power figures?

          • Andrew Heard says

            I’ve never seen any evidence (from my logged power data) of freeze protection mode, or significant power (> 5W) being used inside the block-out time. The unit is very quiet. At midday (non daylight saving time) the system will ramp up to 1kW over the 1st 4 minutes, then slowly/ linearly ramp up to a maximum power a minute before 1pm around 1.3kW.

  27. Many of us have surplus energy during the middle of the day, why not have a simple electric resistance water heater operating in the middle of the day – it’s a fraction of the price to install, lasts longer and is low maintenance- I have evacuated tubes with electric boost and live in Canberra- 60% of the year we have solar – and through winter up to 90mins boost. Had this system for 12 years not sure about wisdom of RSHP

    • I have the same and get cold winters. I have my hws inside to minimise heat loss and freezing (can’t do that with a heat pump that needs airflow and produces cold air).
      My evacuated tubes have reduced in efficiency over time but they still add heat requiring only a small circulation pump.
      Been running for 11+ years and a powerdiverter with our solar seems very efficient to me.
      Total maintenance over that time has been a new solar pump controller ($80).

  28. Mark heath says

    I fitted an iStore 180 unit 2 years ago to replace my aged gas storage unit and it’s a cracker – programmed to come on at 9:00am usually has the water heated inside 2 hours. Runs off my excess solar energy. The only point with the unit is it is huge – much bigger that my old gas storage unit – so if you have limited space please consider. It sits on the old plinth that my gas unit was on – I’m 180cm and need steps to access the programming screen.

  29. “Cheaper heat pumps using R134a or R410a refrigerant can achieve this normally, but when it’s cold, they struggle.”

    Yet, here we have EvoHeat, who are the makers of the widely popular EVO270-1 HPHWS claim:

    “EvoHeat heat pumps use environmentally friendly R410a & R32 refrigerants which are recognised as the green refrigerant in the industry while delivering a safe and stable running performance.”


    ProductReview Link:

    Must be a typo, or what is EvoHeat smoking?

    • Anthony Bennett says

      Hi Sam,

      I suspect you could have them on a charge of false advertising on that one. Those refrigerants are terrible.

      • I am glad I came across your article yesterday, Anthony.
        Also, thank you to Finn for your weekly newsletters.

        I have been eyeing the EVO270-1 HPHWS for awhile whilst praying that my GHWS will die so that I can finally get off gas.

        I will reach out to EvoHeat regarding what refrigerant they actually use since they have cheekily left this info out of their spec sheet / product brochure:

        I suspect it might be the same as iStore (high GWP refrigerant R134a) as they are almost clones of each other.

  30. José RESINA says

    After talking time to read these comments, I was just wondering if it would be possible , faisable to draw warm air from the house in winter to have the HP working above zero and using warm air in summer to cool the house. ?

    • Anthony Bennett says

      Anything is possible José,

      I suspect there might be compromises though. The water heater would rob your house of heat in winter, and going the other way, I imagine the air wouldn’t be very cool taking summer ambient temperature, taking a few degrees off and pumping it into the house.

      Keen to hear if you want to measure some air temperatures on the evaporator inlet and outlet though.


  31. So much of this information is useful to consumers. It is disappointing however that Karl from iStore is the only external person quoted. He does not offer free advice, it is free advertising for iStore. This free advertising also doesn’t include an explicit mention about the fact that iStore has to change the refrigerant used because it is now against regulations due to how bad it is for the environment. I would love to know if you reached out to other hot water heat pump wholesalers or you were just happy to include your mate? This definitely damages the reputation and reliability of Solar Quotes in my mind. I will be less likely to send friends here for reliable information in the future.

    • Anthony Bennett says

      Hi Ceri,

      I take the point you’re making but if we interviewed every manufacturer the posts would be 15 000 word dissertations which nobody would actually read.

      Right now Solar Quotes has leading contributors on holidays and hiatus, so we’re putting out fewer posts overall and pretty proud to be increasing engagement at the same time. We’ve acknowledged that iStore use R134a but if you have any evidence to say they’ve been forced to change refrigerant, please get in touch, we’re perfectly happy to make corrections.

      As for giving iStore a free plug, you might have noticed we give everyone a free plug, whether they like it or not. We simply refuse to take money from manufacturers and it means we can write whatever we see fit.

      I’d encourage you to have a look at My Efficient Electric Home and notice how the top contributors spend countless hours offering valuable expertise for free. Doing sums, making spreadsheets, publishing articles, posting graphs… and most importantly taking the time to explain them to those seeking help.

      Thanks for the feedback.

    • I am with Anthony on this. I have found over the many years I have been on here that the SQ site has been fearless in making and backing its engagement and commentary on manufacturers, importers and installers. I have never felt that any advice the SQ team has given has been negatively affected by their interaction with the industry.

      Maybe it has helped them at times by being able to get information about issues and upcoming developments. Yes it can be seen as a form of advertising but not all advertising is bad – often it helps customers to make informed decisions. However, you cannot possibly know what Karl from iStore’s motives are – no one can know a person’s inner motivations. And without knowing him personally, you cannot even make an informed guess. For all you know he simply wants SQ to do an even better job of helping its customers make good decisions.

      • “However, you cannot possibly know what Karl from iStore’s motives are – no one can know a person’s inner motivations. And without knowing him personally, you cannot even make an informed guess.”

        I think you missed Ceri’s point completely. This isn’t about Karl’s motives.

        I wouldn’t have hurt to have more than one manufacturer feature in this article, which would demonstrate completely impartiality.
        No one is saying that every single manufacturer should be reached out to for commments, as that is simply not practical.

        I would have liked to hear from Sanden or Reclaim Energy (Apricus) who make much more reputable HP HWS products than iStore (or their clones like EvoHeat).

        Sure they cost a whole lot more, but they actually use CO2 as their refrigerant, and offer a stainless steel tank option without the need for a sacrificial anode (almost maintenance free).

  32. Hi. Great Article – thanks.
    I have a Rheem 26 with 2 Hot-water panels (not PV), into a 270L storage tank, and gas “top-up”. Works very well – some 13 years old now.
    My new Rates (Vic) are – Gas 5.0264 cents/Mj; Elec 52.3483 cents/kWh.

    Q: How does this arrangement compare to a Heat-Pump?

  33. I’m somewhat confused about the iStore now,
    Their website claims that R134 is safe
    and after many weeks of confusion about what is best in our situation, I had thought this was the answer.
    Now, I’m not sure.
    Are you able to clarify?
    We currently have a 20 yo NG Instantaneous Rinnai but there is no room on that side of the house for any sort of tank, so need to relocate it to the other side of the house anyway. We also have 8.7kw solar panels (SolarEdge inverter) and run pool pumps during the peak of the day.
    Thank you 🙂

  34. David Walsh says

    With almost 40 years experience with electric boosted solar hot water in my residence and 25 years experience at my short term rental holiday house with electric boosted solar hot water and now 7 months experience with heat pump where one of the two big brand names has only worked reliably for 2 out of the 7 months. Solar hot water boosted by PV electric is hands down the best way to go over the long term. The big problem with heat pump hot water is the lack of experience in trouble shooting installation issues. And the almost impossibility to get someone with both the desire and ability to do trouble shooting and maintenance on the units. There are plenty of plumbers who can connect the heat pumps up but after that the owners are on their own. And if you can get someone to look at your unit not performing then you are paying for them to learn on your time. One of the top two brands does not have a decent manual but the unit has at least internal 13 sensors in the heat pump itself controlling the unit and no proper documentation. With installation this unit cost $10,000 and I am hoping it is now sorted. In my opinion except for limited commercial applications hot water heat pumps do not make sense yet. The price needs to come way down and maintenance expertise much greater.

  35. Paul Lewis says

    I’ve spent the last 3 weeks reading about Heat Pump HWS.

    Whilst I’m still bitter about my Rheem 325, I am considering purchasing another at some stage but not a Rheem.

    I am confused though for several reasons.
    Firstly, very few mention the quality of water you supposed to feed these things, in order to maintain your warranty.
    Secondly I read this morning “…….The heat in the air passes through the evaporator and is absorbed by a natural refrigerant, R744 (CO2), which is ozone friendly and does not contribute to global warming.”

    Whilst my purchase will be about efficiency, the environment will also be a consideration.

    I thought C02 was very bad for the environment or did I miss something?

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