Pool Heat Pump Sizing Calculator for Australian Pools
This free pool heat pump calculator tells you the exact size your pool needs. Answer five quick questions and get the right kW, the models that fit, how long it takes to warm up and roughly what it costs to run.
- Takes about a minute
- Uses the climate for your postcode
- Shows warm-up time and running costs
- Works for pools, spas and swim spas
Heat pumps that fit your pool
Every model below delivers at least the size your pool needs.
How to size a pool heat pump
A pool heat pump is sized in kilowatts (kW) of heat output, and the right number depends on your pool's water surface, how warm you want it, how cold your area gets in the months you swim, and whether you use a cover. For a typical 40,000 litre pool in Sydney kept at 28°C from October to April, that works out to about 19 kW uncovered or 11 kW with a cover.
Pool shops often size by litres alone. That misses the two things that matter most: the climate in your coldest swimming month and the heat you lose off the surface overnight. This pool heat pump sizing calculator sizes for the coldest month you still want to swim in, because a heat pump that copes in October will cruise through January.
Quick sizing guide by pool size
The table shows the heat pump size for a Sydney pool heated to 28°C from October to April, with average sun and wind. Use it as a starting point, then run the heat pump calculator above for your own postcode.
| Pool volume | Uncovered | With a cover |
|---|---|---|
| 20,000 litres | 10 kW | 9 kW* |
| 30,000 litres | 14 kW | 9 kW* |
| 40,000 litres | 19 kW | 11 kW |
| 50,000 litres | 24 kW | 13 kW |
| 60,000 litres | 29 kW | 16 kW |
| 70,000 litres | 33 kW | 18 kW |
*9 kW is the smallest pool heat pump we recommend. Smaller covered pools often need less than that, which simply means a 9 kW unit will warm them quickly.
How much your location changes it
Climate is the biggest swing factor after the cover. The same 40,000 litre pool heated to 28°C from October to April needs three times the heat pump in Hobart that it does in Brisbane.
| Area (40,000 litre pool) | Uncovered | With a cover |
|---|---|---|
| Brisbane | 12 kW | 10 kW |
| Sydney | 19 kW | 11 kW |
| Perth | 23 kW | 13 kW |
| Adelaide | 24 kW | 13 kW |
| Melbourne | 27 kW | 15 kW |
| Canberra | 36 kW | 20 kW |
| Tasmania | 37 kW | 20 kW |
Above about 35 kW, a single residential unit is not enough. Two matched units running side by side is the usual answer, but a cover almost always makes more sense first.
The six things that decide your heat pump size
- Surface area. Most heat escapes through the water surface, so a long, shallow pool needs more than a small, deep one holding the same litres.
- Water temperature. Every extra degree you want adds roughly 10 percent to the size. 28°C is the most popular setting; 26°C is fine for laps.
- Where you live. The calculator uses long-term climate averages for your postcode, from the tropics to Tasmania.
- How long you swim. Stretching from summer only to October through April nearly doubles the size, because you are heating into cooler months.
- A pool cover. Evaporation overnight is where most heat goes. A cover cuts the heat pump you need by around 45 percent.
- Sun and wind. A sunny, sheltered pool holds its heat. A shaded, windy one needs up to 30 percent more.
Why a bit bigger beats too small
An undersized heat pump is the most expensive mistake you can make. It runs flat out, wears harder and still leaves the pool cold after a cool change. A unit 10 to 20 percent above your minimum reaches temperature faster and then idles, and an inverter heat pump slows right down once the water is warm, so the extra capacity costs very little to run.
That is why the calculator gives a range and recommends models from the bottom of that range upward. If you are between two sizes, go up.
What it costs to run
A heat pump does not burn fuel. It moves heat out of the air into the water, delivering around five units of heat for every unit of electricity in mild weather. For the 40,000 litre Sydney example above, expect roughly $1,100 over an October to April season uncovered, or about $600 with a cover, at 33c per kWh. The calculator works this out month by month for your postcode, and our guide to pool heat pump running costs goes deeper.
How accurate is this pool heat pump calculator?
It is an estimate built on long-term Bureau of Meteorology averages, calibrated against the sizes installers use in practice, and it deliberately leans slightly generous so you are never left with a cold pool. Real results vary with unusual weather, heavy shade, water features and very exposed sites.
If you want certainty before you buy, send us your details for a free sizing check or call 1300 930 847. We will confirm the size and the model that suits your budget.
Keep reading
Pool heat pump size: common questions
What size heat pump do I need for a 40,000 litre pool?
For a 40,000 litre pool kept at 28°C from October to April, you need about 19 kW in Sydney, 27 kW in Melbourne and 12 kW in Brisbane if the pool is left uncovered. With a cover on every night, that drops to roughly 11, 15 and 10 kW. Put your postcode into the calculator above for your exact number.
How do I work out what size pool heat pump I need?
Work out how much warmer you want the water than the air in the coldest month you still want to swim, multiply by the water surface area, then adjust for a cover, wind and sun. The calculator does this for you using the climate for your postcode. As a rough rule, an uncovered pool in Sydney swimming October to April needs just under half a kilowatt per 1,000 litres.
Does a pool cover change the size of heat pump I need?
Yes, more than anything else. A cover stops most of the evaporation that drains heat overnight, so in most of Australia a covered pool needs around 45 percent less heat pump and costs a bit over half as much to run. Read more in do you need a pool cover with a heat pump.
Is it better to buy a bigger pool heat pump?
A little bigger is better than too small. An undersized heat pump runs flat out and still leaves the water cold on cool weeks. A unit up to about 20 percent over the minimum reaches temperature faster, then idles, which is why the calculator gives you a range rather than a single number.
How long does a heat pump take to heat a pool?
A correctly sized heat pump usually needs one to three days of running to lift a pool from spring temperature to 28°C with the cover on. A 20 kW unit takes a 40,000 litre Sydney pool from about 20°C to 28°C in roughly 26 hours. After that it only replaces the heat lost each day. More detail in how long a heat pump takes to heat a pool.
How much does it cost to run a pool heat pump in Australia?
For a 40,000 litre Sydney pool kept at 28°C from October to April, expect roughly $1,100 for the season uncovered, or about $600 with a cover, at 33c per kWh. Colder areas and longer seasons cost more. See the full breakdown in pool heat pump running costs.
Can I use this heat pump calculator for a spa?
Yes. Choose Spa or swim spa at the top of the calculator. Spas run hotter and hold far less water, so a typical 1,800 litre spa with the lid kept on needs only about 3 kW, which means any small heat pump covers it. More in our guide to choosing a heat pump for a spa.
Want us to check your numbers?
Send us your pool size and postcode and our team will confirm the right heat pump, free. Australian owned, based in Perth, delivering nationwide.