What Size Pool Heat Pump Do I Need?
A sizing guide for Australian pool owners who want a warm pool without a power bill that makes their eyes water.
Want your exact number? Our pool heat pump sizing calculator uses your pool size, postcode, cover and swimming season to work out the right kW, then shows the heat pumps that fit.
Here is the short answer. For a typical Australian backyard pool, somewhere between 20,000 and 40,000 litres, you want a heat pump in the 13kW to 20kW range. Smaller plunge pools and spas drop to 9kW to 13kW. Big family pools past 50,000 litres climb to 28kW and up.
That gets most people to the right shelf. Now the part that decides whether you land on the right unit or waste a thousand dollars.
Litres first, then three things that change everything
Pool volume is where sizing starts, not where it ends. Two pools of the same size can need very different heat pumps depending on three things.
1. Whether the pool is covered
This is the big one, and almost nobody thinks about it before they buy. An uncovered pool loses most of its heat overnight through evaporation off the surface. Cover it and you keep that heat in.
A pool with a cover can run a heat pump maybe one size down from a naked pool of the same volume. Skip the cover and you are heating the whole backyard. If you are going to spend money anywhere, spend it on a cover before you spend it on extra kilowatts.
2. Your climate and how long a season you want
Brisbane and Perth are not Melbourne and Hobart. A pool in the tropics wants far less grunt than the same pool in a cold southern winter. And a heat pump sized to stretch the season into April and pick it back up in September has to work harder than one that just tops up summer warmth.
Colder climate or longer season means size up. Warm climate, summer only, size down.
3. How fast you want it warm
A bigger heat pump heats the water faster and then idles. A smaller one gets there eventually but runs longer to do it. Neither is wrong. If you plan the water at 28 degrees on tap all season, go bigger. If you are patient and set-and-forget, you can go smaller and save on the purchase.
The sizing table
Rough guide for an uncovered pool, moderate Australian climate, summer-to-shoulder season. Cover the pool and you can usually step one row up (meaning a smaller unit). These are starting points, not gospel.
Pool volume vs heat pump size
| Pool volume | Pool type | Heat pump size |
|---|---|---|
| Up to 20,000L | Plunge pool, small courtyard pool, spa | 9kW to 13kW |
| 20,000 to 30,000L | Small to medium family pool | 13kW to 17kW |
| 30,000 to 40,000L | Standard family pool | 17kW to 20kW |
| 40,000 to 55,000L | Large family pool | 20kW to 28kW |
| 55,000L and up | Large or lap pool | 28kW to 35kW |
Not sure of your volume? Length by width by average depth by 1,000 gives you litres. A 8m by 4m pool averaging 1.5m deep is about 48,000 litres, which lands you in the 20kW to 28kW band.
Where our range sits
We stock pool heat pumps from 9kW right up to 35kW, so there is a match for every pool on that table. A few anchor points across the range.
At the small end, the Guardian Eco Pro 9kW handles plunge pools and spas. Stepping up, the SensaHeat ES 13kW suits small family pools. Mid-range, our best seller is the Midea M Series 20kW with WiFi, which suits most standard family pools and is the one people land on when they follow our Midea 20kW guide. For quiet running and low bills there is the Guardian Platinum 20kW inverter, and at the big end the Guardian Eco Pro 35kW covers the largest backyard pools.
See the whole line-up in Heat Pumps for Pools & Spas.
Prices and models current as of July 2026, AUD including GST.
The mistake that costs the most: buying too small
People undersize to save on the sticker price. It backfires. An undersized heat pump never quite reaches temperature on a cold snap, so it runs flat out around the clock, chewing power and wearing itself out, and the pool still feels cool. A correctly sized unit reaches temperature and then idles, sipping electricity to hold it there.
Oversizing by a little is cheap insurance. Undersizing to save $400 is a false economy you feel every cold morning for ten years.
Running cost, since it is the next question
Heat pumps are the cheapest way to heat a pool that is not solar, and it is not close. They do not make heat, they move it, pulling warmth out of the air and pumping it into the water. For every unit of electricity they draw, a good one delivers five or more units of heat. That ratio is the COP, and it is why a heat pump beats gas and electric element heating on running cost every time.
An inverter model saves more again, because it throttles down to a low hum once the pool is warm instead of switching hard on and off. Full detail on that in our running-cost guide, once it is live.
Frequently asked questions
What size pool heat pump do I need for a 40,000 litre pool?
For an uncovered 40,000 litre pool in a moderate Australian climate, look at 20kW. Add a cover and you could drop to 17kW. In a cold southern winter or for a long season, step up to 24kW.
Is a 20kW pool heat pump enough?
A 20kW unit suits most standard family pools up to around 40,000 litres. It is our most popular size for exactly that reason. Bigger pools, cold climates or uncovered water may want 24kW or more.
Does a pool cover really change the heat pump size?
Yes, more than anything else on this page. A cover traps the heat a heat pump puts in, so a covered pool can often run a size smaller than the same pool left open. It is the single best-value thing you can add.
Can one heat pump run a pool and a spa?
It can, but the spa wants to be much hotter than the pool and holds far less water, so most people size the heat pump for the pool and accept a slower spa. For a spa on its own, look at a dedicated spa heat pump instead.
How much does it cost to run a pool heat pump?
Far less than gas or electric element heating, because a heat pump moves heat rather than making it. The exact figure depends on your pool size, whether it is covered, your climate and your power tariff. A correctly sized inverter model with a cover is the cheapest setup short of solar.
Not sure which size fits your pool? Ask us
Tell us your pool volume, whether it is covered, your postcode and how long a season you want, and we will tell you the exact model that fits. It takes a minute and it saves you from guessing.
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Chasing lower running costs another way? Our Guardian Lux-V full DC inverter range is built for exactly that. Or browse the complete Heat Pumps collection.
This guide is general information for Australian pool owners and is not a substitute for advice on your specific pool and site. Pool heat pumps are electrical appliances and must be connected by a licensed electrician. Confirm final sizing with us or your pool professional before you buy.