Reverse Cycle Not Keeping You Warm? Here’s What To Do.

Winter is here, and nobody is more aware of that than Australians with a struggling reverse cycle air conditioner (RVAC). If your system isn’t keeping you warm, here’s what to do to get it humming.

Reverse cycle systems have plenty of benefits over gas heating – they’re cheaper to run, better for the environment, and present fewer health risks. But some people find they don’t feel quite as cozy. I saw such a complaint from a RCAC owner recently which I’ve paraphrased below:

We live in a cold-climate winter area, and five years ago we replaced our old ducted gas system with reverse cycle air conditioning. We upgraded the ducting too. On paper, the new system ticks all the right boxes — maybe even oversized slightly — but in practice, it’s just not as good at heating. The gas used to warm the house in 30–45 minutes. Now it takes hours.

Yes, it’s probably cheaper to run. But it’s not as comfortable. And while we could improve our insulation, we haven’t changed anything from when we used gas. The comparison between systems is fair in my opinion— and the reverse cycle is losing. To make things worse, defrost cycles in cold weather fire up like radiator mode and plunder your energy bill. Environmental concerns aside, it feels like we’ve taken a step backwards.

If your reverse-cycle aircon isn’t getting it done for you, there’s a few potential adjustments you can make.

If your dog camps near the outdoor air con unit, it may be worth cleaning the coil.

Have You Cleaned The Filter?

Reverse-cycle systems don’t have the brute force of burning gas, but neither do they involve much risk. While poorly maintained gas heaters can kill people with asphyxiation, a RCAC with a grubby filter will just perform poorly.

It’s something I’ve noticed firsthand with an old “weather wall” air con unit in a rental. Built through the wall of a 1970’s house, this thing was not just badly insulated, it was in itself a massive air leak.

It was high summer and this piece of junk was noisy and did nothing, so colour me surprised when removing the inside grille revealed the mouldy mess pictured below. The evaporator coil was absolutely caked in soft, dusty, furry muck.

Obviously, this vile mess wasn’t going to work well. I had to take this image to show my wife what I’m willing to do for the team…

Once cleaned, the air conditioning did work, but in reality it was still just an oversized window rattler. Cleaning the filter on a more modern ducted or split system can make just as big a difference.

With less power comes great responsibility, because increased efficiency means keeping things clean is critical to home comfort.

Chalk and cheese, but cleaning filters in the sink is a breeze.

Dust is beginning to build up on the intake louvres and the screen.

Cleaning A Split System

Split systems and ducted RCAC systems are different beasts, with their own cleaning requirements and challenges.

Cleaning your average split system RCAC is very straightforward.

This is a tangental fan from a high wall split system air conditioner, demonstrating that it pays to make sure the condensate drain is clear.

If your split system is spitting water in summer it may be because the drain line is blocked by grass growth from outside.

Ducted Systems Can Be More Complicated

Long runs of ductwork lose heat quickly — especially in the roof space — and they don’t let you fine-tune room by room. That’s why many energy nerds prefer split systems. They’re more efficient, easier to maintain, and they heat only the spaces you’re actually using.

The truss highlighted in yellow was restrictive in size, hence I watched as the dodgy air contractor stripped the insulation off this section circled to make it fit through. With a flat roof, metal frame and western sun, this will be horrendous.

The return air filter for ducted air conditioning. Undo the thumb nut, swing it down and clean it gently with a hose or vacuum cleaner.

Reverse Cycle Isn’t Weak – It’s Different

Nobody’s pretending reverse cycle has more grunt than a gas burner. It doesn’t, and a direct comparison isn’t really fair because these are different systems using different technology.

To make an analogy, it’s like comparing electric cars to petrol ones — an EV is a fundamentally more efficient device but you can’t expect it to do precisely what a petrol one does because they’re not the same.

They need a different mindset because you can’t refuel on the highway in 5 minutes, but 20 minutes for a coffee to get you to 80% does pretty much the same, without wasting time on 100% charging.

Hold On To Your Heat

If your car was leaking petrol, you’d fix it in an instant. Heat’s no different — it’s just invisible without a thermal camera.

Improving the insulated envelope of your house should be the very first step because it makes things more comfortable, even without turning the RCAC on, plus it improves efficiency too.

Most Australian homes are built like sieves — draughty, under-insulated, and full of cheap oversized single-glazed windows in metal frames that bleed heat. Using a gas or wood fire, the flames in some cases can simply overcome the inefficiencies.

But with RCAC, those problems become more evident. Suddenly you notice the cold air pouring through gaps, the rooms that never feel warm, the whole house as a system is struggling.

Misplaced insulation batt leaves a cold (dark) patch on the ceiling above this RCAC while it’s heating the room.

A Warm Welcome Home

For home heating the trick is to program the RCAC to come on earlier in the day, so the house is warmed up before you get home.

Instead of flogging the heating between 6 & 7pm, give it some time to do the job when the sun is out, which if you have solar means the electricity is basically free. What you’re aiming to do is get the thermal mass of the house under control.

Once you walk in the door to a pleasantly warm house, you can decide to throttle down or even switch off the heating.

Thermal Inertia Is A Thing

My first house was a 1950ish double brick number, with evaporative air conditioning, leaky sash windows and no insulation in the ceiling whatsoever.

There were times I would rock home at 6pm, it was cold and dark, and the house was even colder because nobody had been home all day.

My quick and dirty solution was a 300mm inline fan which sucked air out of the roof space and pushed it inside through the air con ducting (The evap unit was sealed up). There was no fancy thermostat, just a timer which ran the fan from 10am to 3pm.

On average it was warmer in the roof during the day, and I would find the house warmer inside when I got home.

By using the warm air from the roof, I got the internal brick walls, the thermal mass in the house, warmed up for free. Then the RCAC didn’t struggle so much because it had a higher base to work from.

The system I’ve described here is one you could buy as a package from Perth. It was featured on the TV and even had a nice temperature “control” panel. Instead of a dumb timer, it measured the temperature in the roof and when it was 5ºC hotter above the ceiling, the fan came on to move that heat inside. Sadly, this system is no longer available, but I’ll try to resurrect a DIY guide if I can.

Defrost: The Silent Comfort Killer

One of the biggest complaints from cold-climate users, including our RVAC owner at the top of the article, is the dreaded defrost cycle. Just when you need warm air in the early morning, the system shuts down to protect itself — because frost has built up on the outdoor unit.

This is normal, but annoying when (assuming they’ve installed the right system to begin with) a resistive element kicks in to consume a lot of power and fend off the frost.

It’s also another reason to run the system early to maintain steady temperatures. If your unit is constantly battling ice, it’s a sign the system is under strain or the outdoor unit isn’t in an ideal spot.

RCAC unit frozen over

In God We Trust. Everyone Else Brings Data.

If you’d like a different perspective, follow Nate the House Whisperer. He is very good at making heat pumps work in challenging conditions across a range of climates.

Careful planning and real-world data means RCAC can work brilliantly — even when it’s snowing — but only if you treat it as a system, not a standalone box. That means thinking about your house as a whole: insulation, air sealing, zoning, timing, and yes, maintenance.

Bottom Line

People are often unsure of change and see any criticism of RCAC as plenty of reason to stay with pretty expensive and polluting heaters. However once they move to efficient heating, it exposes how much other work needs to be done to overcome the thermal deficiencies.

RCAC doesn’t always hide the flaws in your home the way burning things does. So if it feels like a downgrade, the solution isn’t necessarily a bigger unit — it’s a better setup and smarter use.

And yes — you’ve got to clean the filters.