Are you looking to extend your swimming season and enjoy a warm pool all year round? Installing a pool heat pump could be the solution you need to enjoy your pool longer (during the colder months) with proper pool heating. However, to ensure maximum efficiency and avoid overspending, it is crucial to select the right size heat pump. In this article, we will guide you through the process of properly sizing a pool heat pump to help you make an informed decision.

Why is Proper Sizing Important?

A pool heat pump operates by extracting heat from the surrounding air and transferring it to the pool water. The rate of heat transfer depends on the size of the heat pump, which is measured in KW (Kilowatts). If you choose a pump that is too small, it will struggle to heat the water, leading to high energy consumption and long heating times. On the other hand, if you select a pump that is too large, you will end up wasting energy and money. Therefore, proper sizing is essential to achieve optimal performance and energy efficiency.

Step 1: Determine the Required KW’s

The time needed to heat a pool depends on how big the heat pump that you have is, the volume of the pool and the heat loss from the surface of the water in the location you are in.

Depending on what month of the year it is, the first time you switch on the heat pump you can expect a temperature rise of between 0.1 and 0.3 degrees per hour. This also depends on the heat pump installed as well. For a quick guide to calculate how many hours it will take to heat the pool is a calculation

(pool volume x 4.18 x temperature rise)/ 900

Then divide the answer by the KW of the heater chosen and that is the approximate number of hours the heater will need to run to achieve your target temperature. If you use the average ambient temperature for the coldest period you would like to have the pool heated in this equation the required size would be the one that gives you less than 11 hours of runtime per day

(Note this is just to heat up the water and doesn’t take into consideration the heat loss during heat up and other environmental factors, this is where a pool cover can help)

A heat pump is designed to maintain a pool temperature by running everyday. This ensures that the water doesn’t return to ambient temperature in the cooler months leading to extended running times.

Note that a pool heat pump size for Extended season only will not be able to achieve the set temperature in the winter months.

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Step 2: Determine the Heat Pump Capacity

Now that you know the required KW, you can select a heat pump that can deliver that capacity. Heat pumps are available in various sizes, ranging from 9KW to 40KW for residential applications, and up to 250KW for commercial heat pumps. To ensure proper sizing, you should choose a pump that is within 5% of the calculated KW.

For example, if you calculate that you need a heat pump with a capacity of 20KW, you should select a heat pump that delivers between 19KW and 21KW.

Step 3: Consider Other Factors

In addition to pool size and desired temperature rise, there are other factors to consider when sizing a pool heat pump, such as:

Efficiency rating

Look for a heat pump with a high COP (Coefficient of Performance) rating, which indicates how efficiently the pump converts energy into heat. A higher COP means lower operating costs.


The location of the heat pump can affect its performance. Ideally, the pump should be installed in a well-ventilated area with plenty of airflow.

Pool usage

Consider how often you use your pool and for how long. If you only use it occasionally, you may not need a high-capacity pump.

Solar Panels

If you have solar PV panels on your roof you may want to select a larger heat pump with reduced running hours in the shoulder season. This will allow you to maximise the solar production hours during the day, and limit the running hours of the heat pump to sunlight hours while still achieving your desired temperature.

Follow these steps to get the right heat pump for your pool

Selecting the right size of a pool heat pump is crucial for efficient and cost-effective operation. By following the steps outlined in this article, you can determine the required BTUs and choose a pump that meets your needs. Remember to consider other factors such as efficiency, location, and usage to make an informed decision.

If all else fails, ask the experts at Clarity Pool Management in Sydney to visit your pool and help you find the one that’s right for you.

Contact us today!