Most people buy pool heating twice. The first time they buy on price, and the second time they buy on understanding. This article is an attempt to save you the first purchase.
A pool heat pump is the most misunderstood piece of equipment in the average Aussie backyard. People assume it works like a kettle, or like the gas heater their neighbour has, and then they're baffled when it behaves nothing like either. The confusion is understandable, because a heat pump does something genuinely counterintuitive. It doesn't create heat at all.
The bit everyone gets wrong
A gas heater burns fuel. An electric element glows. Both of them manufacture heat out of energy, and both are limited by simple physics: you can never get more heat out than the energy you put in.
A heat pump sidesteps that limit entirely, because it isn't in the manufacturing business. It's in the removals business. There's already an enormous amount of low-grade heat sitting in the air around your pool, even on a cool morning. The heat pump's only job is to collect that heat, concentrate it, and carry it into your water.
That's why the efficiency figures look implausible when you first see them. You're not paying to create warmth. You're paying to run a fan and a compressor that relocate warmth that was already there and free.
The cycle, step by step
Strip away the marketing and there are four things happening in a loop.
Step one: the fan draws air across the evaporator. Inside the evaporator sits refrigerant, a fluid chosen specifically because it boils at a very low temperature. Ambient air that feels cold to you is more than warm enough to make it boil.
Step two: the refrigerant absorbs that heat and turns to gas. This is the collection stage. The air leaving the unit is now noticeably cooler than the air that went in, because some of its heat has been taken.
Step three: the compressor squeezes the gas. Compressing a gas raises its temperature dramatically. The diffuse, low-grade warmth pulled from the air is now concentrated into a small volume of very hot gas. This is the only stage doing serious work, and it's where most of your electricity goes.
Step four: the heat exchanger hands the heat to your water. Pool water is pumped past the hot refrigerant, picks up the heat, and returns to the pool a fraction of a degree warmer. The refrigerant cools, returns to liquid, and the loop starts again.
Your pool doesn't warm up in one dramatic burst. It warms up because that loop runs thousands of times.
Why it takes longer than you expect, and why that's fine
New owners often panic in the first week. They switch the unit on, check the pool three hours later, and find it's barely moved.
A pool holds an enormous mass of water, and water is stubborn. Raising the temperature of tens of thousands of litres by a single degree takes real energy no matter what's supplying it. A pool heat pump does this gradually and cheaply, which is exactly the trade-off it's built around.
The practical upshot: heat pumps reward people who leave them running. Set your temperature, let the unit hold it, and it will sip power maintaining what it's already achieved. Switching it on the morning of a party is the one scenario a heat pump handles poorly.
What actually changes performance
Four things move the needle, and only one of them is the unit itself.
Air temperature. Colder air holds less available heat, so output drops as the mercury falls. Every unit has a minimum operating temperature.
Whether you use a cover. Evaporation is the single biggest source of heat loss from any pool, by a wide margin. An uncovered pool is a machine for throwing warmth at the sky overnight.
Your target temperature. The gap between your water and the surrounding air is what drives heat loss. Holding a pool at a comfortable swimming temperature costs far less than pushing it several degrees higher.
Correct sizing. An undersized unit runs constantly and never quite arrives. An oversized one is capital you've spent for nothing.
Heat pump or gas?
The honest answer is that they solve different problems.
Gas is for people who use their pool unpredictably and want it hot within hours, and who accept a high cost per session for that privilege. Holiday homes and rarely-used entertainers' pools genuinely suit gas.
A heat pump is for people who want to swim regularly and want the running cost to stay sensible. It's slower to arrive and far cheaper to stay. For most Australian households swimming through the shoulder seasons, that's the better maths.
Frequently asked questions
Can a pool heat pump cool my pool?
Reversible models can. In parts of Australia where pools become uncomfortably warm through summer, running the cycle in reverse to pull heat out of the water is a genuine feature rather than a novelty.
Do heat pumps work in winter?
They work in cooler air, down to each model's rated minimum. Output drops as the air cools, so a unit sized only for summer will struggle in July. If year-round swimming is the goal, that has to be built into the sizing from day one.
How noisy are they?
There's a fan and a compressor, so there's some sound. Inverter models generally run quieter at part load because they aren't constantly slamming between full power and off.
How long do they last?
A well-installed, well-maintained unit is a long-term piece of equipment rather than a consumable. Water chemistry matters enormously here, as does giving the unit clear airflow on all sides.
Where to from here
If you've read this far, you already understand pool heating better than most people who own it. The next step is matching a unit to your actual pool, your actual climate and how you actually swim.
Have a look through the full EvoHeat pool heater range, or if you'd rather skip straight to a sizing answer, request a free personalised pool heat report.
