What Size Heat Pump Do I Need for My Pool? kW by Volume

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What size heat pump do I need for my pool? For a covered 50,000 litre pool heated October to April, published sizing methods land between about 15 and 27 kW of heat output: 16 kW in Sydney and 27 kW in Melbourne on one maker’s table. Without a cover, the same table roughly doubles the size, to 32 and 48 kW.

The short answer

Warming 50,000 litres by 1°C takes 58 kWh of heat (USGS: 4,184 joules per kilogram per degree). Raising it from 18 to 26°C takes about 465 kWh before any losses.
Two makers’ quick rules for 50,000 litres: 14.5 kW and 20 kW. One sizes for at most 4 hours per degree; the other divides volume by 2,500 and says that assumes a cover.
The cover matters more than the volume: one maker’s table gives a 50,000 litre Sydney pool 16 kW October–April with a cover and 32 kW without.
Season length is the next biggest lever: the same covered Sydney pool goes from 9 kW for November–March to 32 kW for all-year heating on that table.
The kW on the box is heat output at warm test air: one maker’s brochure rates a unit at 22.5 kW in 27°C air and 15.0 kW in 15°C air, about two-thirds as much.

Heat pump size by pool volume, October to April: physics, two makers’ quick rules and one maker’s city table, with and without a cover (kW of heat output; read 4 October 2026)
Pool volume	Heat to warm the water 1°C (physics)	Maker A rule: no more than 4 hours per °C	Maker B rule: litres ÷ 2,500 (assumes a cover)	Maker A table, Sydney, cover / no cover	Maker A table, Melbourne, cover / no cover
30,000 L	34.9 kWh	8.7 kW	12 kW	9 / 20 kW	20 / 27 kW
40,000 L	46.5 kWh	11.6 kW	16 kW	13 / 24 kW	22 / 40 kW
50,000 L	58.1 kWh	14.5 kW	20 kW	16 / 32 kW	27 / 48 kW
60,000 L	69.7 kWh	17.4 kW	24 kW	20 / 40 kW	40 / 69 kW
70,000 L	81.4 kWh	20.3 kW	28 kW	Not published: table stops at 60,000 L	Not published

What decides the size: four questions before any kW figure

Volume. Length × width × average depth in metres, × 1,000 for litres. One maker’s guide works a 4 × 6 m pool at 1.5 m average depth to 36,000 litres.
Season. November–March, October–April, September–May or all year. One maker’s table changes more between these rows than between pool sizes.
Cover. Whether the pool is covered when nobody is in it. VBA Practice Note 05-2018 restates the building code: where a pool is heated by a gas heater or heat pump, it ‘must be provided with a cover and a time switch’; the heater timer and cover rule sets out the provision.
Climate. A heat pump draws its heat from the air, so a colder city needs a bigger unit for the same pool and season.

Target temperature matters too: one maker’s guide says 24–28°C is ideal for swimming, and the sizing tables below assume 28°C.

A pool heat pump is sized by season and cover first and by volume second, which is why two 50,000 litre pools can need 16 kW and 48 kW.

Pool heat pump size calculator: the worked calculation for 50,000 litres

Step 1, the physics. The USGS gives water’s specific heat as 4,184 joules per kilogram per °C. A litre of water is about a kilogram, so 50,000 litres needs 50,000 × 4,184 = 209 million joules, or 58.1 kWh, for each 1°C. Taking the pool from 18°C to 26°C is 8 × 58.1 = 465 kWh of heat.

Step 2, the time you will allow. One maker’s method says the heat pump should need no more than 4 hours per 1°C, because night-time heat loss can reach 2°C, which then takes 8 hours to recover. 58.1 ÷ 4 = 14.5 kW. Another maker’s quick rule divides volume by 2,500: 50,000 ÷ 2,500 = 20 kW, and says this is for extending the season with a pool cover. At 20 kW the 465 kWh warm-up takes about 23 hours of running; at 14.5 kW, about 32 hours. That second maker puts typical warm-up at 24–48 hours.

Step 3, the losses. Those rules ignore most heat loss, which is why one maker’s city table is larger: it allows for evaporation, wind and night-time cooling in each city. Without a cover the table’s figures are roughly double the covered ones in Sydney.

Step 4, the electricity. A heat pump moves heat rather than making it. One maker’s brochure lists coefficients of performance of roughly 5 to 8 in 15°C air across its range. At those figures, the 465 kWh warm-up uses about 58 to 93 kWh of electricity. Multiply by your tariff; solar vs gas vs heat pump pool heating compares the season-long running costs.

One maker’s own worked example prints 52.33 kW for a 40,000 litre pool heated 10°C over 40 hours; the inputs it states give 11.6 kW. Check any calculator’s arithmetic before you buy on it.

For a 50,000 litre pool, the physics floor is 58 kWh per degree, and quick sizing rules turn that into 14.5–20 kW for a covered pool.

What size heat pump for a 50,000 litre pool, by city and season

One heat pump maker publishes estimated unit sizes for a pool heated to 28°C with a maximum of about 10 hours’ running, by city and by season, with and without a thermal cover. For 50,000 litres (kW of heat output, cover / no cover):

Season	Brisbane	Sydney	Melbourne
November–March	9 / 9	9 / 16	20 / 32
October–April	16 / 22	16 / 32	27 / 48
September–May	24 / 40	24 / 48	40 / 60
All year	32 / 48	32 / 69	48 / 80

The maker says some sizes need two or more units, that larger surface areas lose more heat, and that the table is a guide only. Some of its other columns are hard to reconcile: in its Canberra column the covered and uncovered figures are identical at 50,000 litres. Use it for the order of magnitude, then ask the installer to show their own calculation.

On one maker’s table, covering a 50,000 litre Sydney pool halves the heat pump it needs for an October–April season, from 32 kW to 16 kW.

Which size is wrong for whom

About 9 kW on a 50,000 litre pool is enough on that maker’s table only in Townsville (uncovered, up to October–April), in Brisbane for November–March, or for a covered Sydney pool November–March. It is wrong for anyone wanting a longer season further south.
14.5–20 kW, the quick-rule sizes, fall short for an uncovered pool in Sydney or Melbourne from October to April (32 and 48 kW on the table), and for Melbourne beyond November–March even with a cover (27 kW).
40 kW and up is wrong for a covered pool in Brisbane or Sydney heated October–April, where the table asks for 16 kW; the extra capacity is money spent on hardware you would not use.

Read the rating conditions. One maker’s brochure lists the same unit at 22.5 kW in 27°C air with 27°C water, and 15.0 kW in 15°C air with 26°C water: a third less. A unit sized on its warm-weather figure is undersized on the cool shoulder-season nights it was bought for.

Prices for units and installation vary with brand, electrical work and pipework, and we have not verified a range we would stand behind. Ask at least three installers to quote the same kW at the same rating conditions, with the cover and time switch listed, then compare pool quotes. Listed pool businesses in Brisbane, Sydney and Melbourne are a starting point.

The kW rating of a pool heat pump means little until you know the air temperature it was measured at.

Common questions

What size heat pump for a 50,000 litre pool?

About 14.5–20 kW on two makers’ quick rules for a covered pool. One maker’s city table gives 16 kW in Sydney and 27 kW in Melbourne for a covered pool heated October–April, and 32 and 48 kW uncovered.

How do I calculate pool heat pump size?

Volume in litres × 4,184 joules ÷ 3.6 million gives kWh per °C; the USGS gives the 4,184 figure. Divide by 4 hours per degree for one maker’s minimum, or divide litres by 2,500 for another’s quick rule.

Is a bigger pool heat pump better?

Only up to the size your season and cover need. One maker’s guide says to round up rather than down between sizes, but a unit well past the table figure costs more to buy without heating any better.

How long does a heat pump take to heat a pool?

A 50,000 litre pool needs about 465 kWh to go from 18 to 26°C, so about 23 hours at 20 kW before losses. One maker puts typical warm-up at 24–48 hours.

Does a pool cover change heat pump size?

Yes, a lot. One maker’s table roughly halves the size for a covered Sydney pool. VBA Practice Note 05-2018 restates the building code: a pool heated by a heat pump must have a cover and a time switch.

Sources

General information only, current at 2026-10-04. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.