What Size Swimming Pool Heat Pump Do I Need?

Heat pumps offer one of the most cost-effective and energy-efficient methods of heating your pool water, ensuring you can enjoy the swimming season for longer and with reduced heating bills! 

To get the most out of your swimming pool heat pump, you must be sure it is sized correctly. Follow our top sizing tips to equip your pool with the right heat pump. 

What Factors Affect Pool Heat Pump Sizing? 

When we talk about sizing for heat pumps, we typically don’t mean the physical size of the unit but rather the energy output. 

There are a couple of things you’ll need to consider when working out what size heat pump is most suitable for your pool. 

  • The size of the pool: A larger pool with more water to heat will require a bigger, more powerful heat pump.
  • The climate and average air temperature: Air source heat pumps draw heat from ambient air temperature, so if you live somewhere colder, your heat pump will have to work harder to get your water up to the desired temperature (e.g. 28°C).
  • Your swimming habits and the frequency of use: If you want to use a heat pump all year round, you may require a larger one that can provide consistent temperature in the colder months.
  • The type of swimming pool: Indoor and outdoor pools, as well as in-ground or above-ground pools, will have different heating requirements. 

The benefits of air source heat pumps for your swimming pool

How Does Pool Volume Affect Heat Pump Size? 

The size of your pool is the most obvious and easily measured factor that’ll determine the necessary heat pump size. The more water a pool contains, the greater the energy requirements to heat all the water. 

How to Calculate the Pool's Volume

When you size a pool heat pump, you will need to know the pool’s volume. 

The average outdoor inground pool in the UK is around 10m x 5m with an average depth of 1.5m. Using these figures, a standard swimming pool would have a volume of around 75m3. 

To work out the volume of your pool, please use our swimming pool volume calculator

How Does Climate Affect Heat Pump Size? 

If you live in a colder climate, then your heat pump will need to work much harder to increase your water temperature. This is because they rely on ambient air temperature to transfer heat into the water via a heat exchanger. 

Air source heat pumps will continue working in cold weather but will become slightly less efficient. If you want to use a heat pump during the extended season from April to November, a larger, more powerful unit will probably be more appropriate. 

Aqua Inverter Turbo-Pro Silence Heat Pumps can operate in air temperatures as low as -15℃ and are available in various sizes to correspond with your pool volume. 

An outdoor swimming pool on a sunny day

How Do Swimming Habits Affect Heat Pump Size? 

Swimming habits have less of a direct impact on pool heat pump sizing but you may still need to factor it in. 

As the technology is so efficient, a standard-sized heat pump for your pool size should be sufficiently robust and reliable, providing the right level of heating throughout the swimming season. 

What's the difference between standard & inverter heat pumps

How to Calculate The Ideal Pool Heat Pump Size

The heating capacity of your heat pump is measured in kilowatts (kW). The more powerful the heat pump, the quicker it’ll be able to heat up a pool and the more suitable it’ll be for higher-volume pools. 

Pool Heat Pump Sizing Calculator

Please note that the below table provides a rough guide only, as the factors mentioned above may have a significant impact on how large you need the heat pump to be. Different heat pumps also have varying coefficients of performance (COP), meaning specific models have different power needs. 

We would recommend finding a heat pump model with all the features that suit your needs and then checking the manufacturer’s notes to determine which size you may require. All of our heat pumps come with handy tables for you to refer to. 

As a basic guide to help steer you in what to look for, here are some averages from across our pool heat pump range. 

Pool volume (m3) Heating capacity in cold air (15C) Heating capacity in warm air (26C)
20-40 6kW 8kW
40-60 9.5kW 13kW
60-80 15kW 25kW
80-100 18kW 30kW


Should I Oversize My Pool Heat Pump? 

Our different heat pumps range from 3.5kW to 32kW. 

If you’ve looked around at various heat pump calculators and the recommendations for your pool hover between a few sizes, it usually pays to size up rather than down. 

The more powerful the heat pump, the quicker it’ll heat up your water – and once it’s up to the desired temperature, it only requires a little bit of energy to maintain. Larger heat pumps tend to have higher coefficients of performance (you get more heat out than energy that goes in), so may be more efficient than smaller units. 

Balance this thinking against the size and specs of your pool though, as you won’t need the largest possible heat pump for a smaller than average pool or one that has good levels of insulation and measures against heat loss! 

To find out more about choosing the perfect heat pump for your pool, check out our advice guide. 

A guide to swimming pool heat pumps: costs, prices & options

If you have any questions about our heat pumps and which one is right for you, please get in touch with the 1st Direct Pools team on 0333 900 4040.