What Size Heat Pump Do I Need for My Pool?

Pick a heat pump that is too small and it will never warm your pool. Too big and you have overpaid for power you cannot use. The right size comes down to one number: how much water your pool holds. Here is how to work it out, then the right heat pump for your pool.

Quick answer

Your heat pump size depends on your pool’s water volume. Work out the volume in litres and divide by about 2,500 for a rough kilowatt (kW) figure, then round up. As a guide, a 25 m³ pool suits a 13kW pump, a 65 m³ pool needs around 32kW, and a commercial pool can need 60kW or more.

How to work out your heat pump size

Three quick steps. You only need a tape measure.

Step 1: Find your pool’s volume

Measure your pool in metres, then multiply: length × width × average depth = volume in cubic metres. A 4m by 6m pool with an average depth of 1.5m is 4 × 6 × 1.5 = 36 cubic metres.

Step 2: Turn it into litres

Multiply cubic metres by 1,000. So 36 cubic metres = 36,000 litres.

Step 3: Divide by 2,500 for a rough kW

36,000 ÷ 2,500 = about 14kW. That is your starting figure. If it lands between two models, always round up, never down.

Size up in two cases: if your pool has no cover or is exposed to wind, it loses heat faster, so add 20 to 30%. A cover is the best way to keep heating costs down. You do not have to guess, though: every Fairland heat pump has an official sizing chart, and we will match your pool to the right model.

Which Fairland heat pump for your pool

We fit Fairland across the range, from a family pool up to a commercial one. Fairland has led inverter heat pump technology for over 20 years, and the pool trade press has recognised it: the industry publication Eurospapoolnews reported Fairland’s X20 as the industry’s first COP20 pool heat pump, meaning up to 20kW of heat for every 1kW of electricity in ideal conditions. Here is which model suits which pool.

Small and medium pools: Fairland InverX Horizontal

Best for: pools from about 20 up to 75 m³. Search terms: small pool heat pump, Fairland InverX, 13kW pool heat pump. The Fairland InverX Horizontal starts at 13kW, for a covered pool up to 25 m³, and rises through 17, 22, 26 and 32kW for larger pools. Why it suits a family pool: it runs down to -15°C air, so it heats all year, and its TurboSilence inverter drops as quiet as 23 dB, about the level of a whisper, so it will not annoy you or the neighbours. The booster mode heats the pool fast at the start of the season, then it settles to around 50% power to hold temperature cheaply. For most family pools, this is the one.

Large pools: Fairland X20 InverX

Best for: larger pools up to around 90 to 160 m³. Search terms: large pool heat pump, 40kW pool heat pump, Fairland X20. The Fairland X20 InverX comes in 14, 16, 18.5, 22, 26.5, 32 and 40kW options. Why it suits a large pool: a big pool costs the most to heat, so efficiency matters most, and the X20 was reported by trade press as the first pool heat pump to reach COP20. It heats and cools, and carries a 7-year parts warranty. For a big pool you swim in most of the year, this is the workhorse.

Commercial pools: Fairland InverX Jumbo

Best for: hotels, gyms, clubs and public pools. Search terms: commercial pool heat pump, 60kW pool heat pump, Fairland Jumbo. The Fairland InverX Jumbo comes in 60kW and 120kW, built to heat large volumes all day, every day. Why it suits a commercial pool: a public or hotel pool runs constantly, so a small efficiency gain becomes a large saving over a year, which is where Fairland’s inverter efficiency pays back fastest. Commercial sizing is not a guess, so we size it to your pool and your opening hours.

Plunge pools

Best for: very small pools under about 10 m³. A plunge pool holds so little water that even our smallest Fairland unit is more than it needs. Talk to us and we will recommend the most sensible option, not more pump than you will ever use.

Get it sized properly

Browse the full pool heat pump range, or read our pool heating guide for the bigger picture. Send us your pool’s length, width and depth, and whether you have a cover, and we will tell you the exact Fairland model you need. It is free, and it saves you buying the wrong one.

FAQ

What size heat pump do I need for my pool? Work out your pool volume in litres (length × width × average depth × 1,000), then divide by about 2,500 for a rough kW figure, and round up. A 25 m³ pool suits a 13kW unit, a 65 m³ pool around 32kW, and a commercial pool 60kW or more.

What happens if my heat pump is too small? It will run constantly and still struggle to reach temperature, especially in cooler weather. It is better to size up, so the pump reaches temperature and then ticks over efficiently.

Do I need a bigger heat pump if I have no cover? Yes. An uncovered pool loses a lot of heat from the surface, so add 20 to 30% to your calculated size. Fitting a cover is the cheapest way to cut heating costs.

Is a bigger heat pump always better? Not always. Oversizing wastes money up front. The aim is a pump matched to your pool volume, then rounded up a little for heat loss, not one far bigger than you need.