If you’re curious about heat pump hot water systems and want an introduction to the technology, here’s the perfect place to start. Discover how these systems work and the different types available, efficiency, costs, solar integration, and more.
If you’re looking to learn *everything* you need to know about how they work and choosing a system, then SolarQuotes founder Finn Peacock’s comprehensive guide to hot water heat pumps is for you. But if you’re just heat-pump-curious or want the nuts and bolts so speak, then the video above and this explainer cover the essentials.
All-In-One Vs Split Units
Hot water heat pumps are available in two forms – split systems where the compressor unit and tank are separate, and all-in-one (aka AIO or integrated) units where the compressor and such are integrated on top of the tank. Split systems tend to have slightly better efficiency, water heating rates and noise levels, while all-in-one units have a smaller footprint, less external pipework, are easier to install and are often cheaper than split systems.
How Hot Water Heat Pumps Work
A heat pump hot water system takes heat out of the air and transfers it into the water.
A fan draws air into the unit over an evaporator coil. Heat from the air turns liquid refrigerant into a gas. The liquid refrigerants used have a very low boiling point – for example, carbon dioxide’s (R744) boiling point at 0.5 MPa is -25°C. Another example refrigerant is propane (R290), which has a boiling point of -10C.
The gas is then pumped at high pressure through a valve by a compressor further increasing its heat, while cool air exits the heat pump. A condenser coil transfers heat to the water. As the refrigerant cools and mostly condenses back into a liquid, it’s cooled further after flowing through expansion valve and the process starts again. Thermostats and other controls regulate the heat pump’s operation.
Hot water heat pumps store water at least 60°C to prevent Legionella bacteria growing, but deliver it below 50°C to prevent scalding – this is handled by a mixing valve.
Hot water heat pumps are generally pretty quiet in their operation: 37–55 decibels; which is quiet fan to fridge territory.
Efficiency/Energy Use
Heating water is one of the most energy-intensive activities in our homes.
A conventional electric resistive hot water system has an efficiency of around 100%. While the real-world efficiency of really crappy hot water heat pumps is also close to 100%, good budget units can have average efficiency of 350% to 400%, and the top-end models up to a claimed 500%.
Basically, for every unit of electrical energy, good hot water heat pumps can amplify this up to five times in heating energy. This amplification is known as “Coefficient of Performance” – or COP. For example, a unit with 350% efficiency will have a COP of 3.5.
Given Australia’s conditions, using a hot water heat pump basically anywhere south of Brisbane is hands down the most efficient way to heat water. They move heat rather than creating it, consuming way less energy than a conventional hot water system using an element. But some heat pumps also include a backup element in case you’re caught short.
Integrating With Solar Power
A heat pump’s low power draw of around 500 – 1,000 watts means they are perfect to use with solar power systems. It’s a great way to make use of surplus solar energy instead of exporting it to the grid for what has increasingly become a pittance in terms of feed-in tariffs. Consider a hot water heat pump as a battery of sorts.
Many heat pumps will come with a timer, which is useful for setting the “solar window” and/or avoiding periods when grid electricity is at its most expensive. And that leads on to an important point – minimising mains electricity use when it isn’t being powered from your panels. How little it uses isn’t just down to your solar panels and the quality of the system, but also installation quality.
A good hot water heat pump system installation not only features a well- insulated tank, but the hot water pipes including elbows, valves and the first 300mm of drain should be insulated with good quality UV-stabilised material.
Costs And Rebates
Prices for heat pumps can vary wildly, but a general rule of thumb is sub-$2,000 models are noisy, inefficient, use nasty refrigerants and are often unreliable. At the other end of the scale are units costing $5,000. Some of these may be worth the money, but others not so; and we’ll get to recommended brands in a bit.
Whether you opt for a budget or high-end unit, the good news is there are financial incentives available to bring down the cost of buying and installing a system.
One of those incentives are Small-scale Technology Certificates (STCs), usually offered as an up-front discount and available nationally. Depending on the unit and several other factors, they can knock about $750 off the price. In addition to STC’s, some states have their own incentive programs – including Victoria (up to $1,200 off), New South Wales (up to $670), South Australia (up to $850) and the ACT (ACTEW AGL up to $1,250 + $250 credit).
STC subsidies and other incentives are further explained in Finn’s full guide.
Maintenance And Warranty
Hot water heat pumps are relatively maintenance free – but all glass lined tanks have sacrificial anodes that will need to be replaced every 3 to 5 years depending on the manufacturer’s instructions. Failing to do so can void the warranty.
Just on warranty, don’t settle for less than 5 years on the heat pump bits and 10 years on the tank – and check warranty details carefully for any gotchas or additional maintenance required.
Recommended Hot Water Heat Pump Brands
Like solar panels, inverters, home batteries and electric cars, we’re spoiled for choice for heat pumps in Australia. And too much choice can lead to confusion.
Navigating datasheets, technobabble and manufacturer claims can be a time-sucking exercise. If you’d like a short-cut through all that, check out the SolarQuotes recommended heat pump brands chart listing manufacturers from budget through to high end that Finn would currently recommend to a friend.
But remember, even the best gear can be ruined by lousy installation!
If this explainer and the video above has left you wanting more information, read Finn’s full hot water heat pump guide here. It also includes a comparison table of models available in Australia along with estimated pricing of each.
About Michael Bloch
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Nuts and bolts so *to* speak.
“Another example refrigerant is propane (R290), which has a boiling point of -10C.”
The Internet says -42.1 C
Good to know about the split systems, in Canada nobody has a water heater outside, and we seldom want to suck heat out of the house between August and May.
As the video says it’s the boiling point at the heat pump operating pressure.
Yes heat pumps heat the water most efficiently but a resistive costs half as much lasts twice as long as there’s no moving parts makes no sound and with reasonable size solar and a green catch diverter both can heat the water for FREE
It costs a lot to get a electrician and heat pumps break down more than resistive
You only get the subsidy on the 1st one but remember what previously mentioned half the price lasts twice as long !! Speaking from actual experience !!
You state that “anywhere south of Brisbane is hands down the most efficient way to heat water”
If i live north of Brisbane does that mean a heat pump isn’t for me?
Or does it mean there are other things to look at, but it might still be a viable option?
Hi Andrew,
North of Brisvegas the amient temperature isn’t as low and the sun hours are high, so a solar hot water service can still be a great option.
I installed a lot of Solahart units myself, close coupled ones with the tank on the roof are simplest and most reliable. I wouldn’t favour a split system with a pump but some installers will point out your house isn’t designed for the extra weight of a 300 litre tank on the roof. A couple of sensibly placed props usually fixes them pragmatically, without engaging a structural engineer.
Glass tube collectors are the best thing ever but cheap chinese roof mount units aren’t. I wouldn’t install a cromagen if you paid me.
Cannot understand why heat pumps are being considered as a tank with a resistive element is cheaper and does not break down and is noise free.
If you have solar and a time clock, a diverter or an inverter like Fronius, which can be set to give a 12VDC signal once the 2,400W solar production is available, then that is definitely the cheapest H/W option.
Dominic Wild: – “Cannot understand why heat pumps are being considered as a tank with a resistive element is cheaper and does not break down and is noise free.”
The upfront costs of a resistive element hot water heater system (REHWS) is undeniably cheaper than a reliable, high-efficiency heat pump hot water system (HPHWS). But considerable energy savings/lower running costs are realized over a period of time with a reliable, high-efficiency HPHWS relative to REHWS.
My HPHWS has already paid for itself – a Sanden 250 litre stainless steel tank split system installed Aug 2015. Lower running costs are the ongoing rewards.
With inadequate solar, a heat pump would eke out the limited energy supply.
But off-grid here, the 46 kWh battery was topped up by mid morning, then 21.5 kWh went into the EV. Now the resistive HWS is absorbing afternoon production excess – without any expensive less-reliable whizzy-go-round ironmongery with eventual piston wear. I can though hear bubbling in the tank, as it’s indoors, so it’s not totally silent. But it is cheaper, due to zero grid cost.
The solar panels are subsidised, so fill the roof. (Now where have I heard that? 😉 With enough of them, and an adequate inverter, the HWS can be a reliable low cost 10 kWh thermal battery.
Had a hot water heat pump installed. It was one in Finns Expensive and Good category. Suddenly stopped working. The original plumber who installed it had retired shortly after installation. Finally found a plumber to look at it he could not figure it out but said they had expelled some air from the line between the compressor unit and the tank but still did not work, and plumber gave up. For three months I tried to find another plumber to look at it, They were all ones who did installations but everyone said they were not skilled to do any service work. During the three months I regularly switched on the unit but no hot water. I was relying of a second hand resistive unit that I got temporarily connected. Finally after a dozen refusals of area plumbers I found a second one who would come. The night before the appointment I tried for the umpteenth time to switch the heat pump unit back on and it suddenly worked after three months. There are 13 sensors so lot of possible problems.
a 2000 watt PV array panels costing 28c per watt will generate about 8kwh per day, which will provide all the electricity for a resistive HWS for most couples who shower each day.
a heat pump can be run for 1/3 to 1/4 as much electricity, so lets say we need a 600watt PV array to provide this.
The difference of 1400Watt pv purchased at 28cents is only $400 more for the extra panels so you can run your resistive HWS for no more cost than the Heat pump,… but the heat pump will cost the best part of $2 to $4000 more, last 1/2 as long as the resistive HWS, while the solar panels will last 4x as long as the heat pump.
The other advantage of extra solar PV is the greater opportunity to utilise more free sunshine power when there is less sunshine, but still heat the water when you would otherwise give the surplus away for tuppence FIT.
And as said before by others, there is no rebate when you have to replace the heat pump, so full tote next time.
I forgot to add in my earlier post resistive can heat the water much hotter if you so wish !!
The green catch is set on solar
only 99% of the time so only miss out on the lousy fit which is getting lousier in Victoria
totally understand where you are coming from… and this conundrum has had me over-analysing my options between replacing my old resistive element HWS with a heat pump… I’m looking at jumping on the Battery bandwagon and only now am I contemplating putting the heat pump HWS in as I don’t like the idea of the HWS service stealing all my battery storage when we have overcast days…. Even though the numbers aren’t adding up!!!