What size heat pump do I need for my pool?

What size heat pump do I need for my pool?

Electric heat pumps are the most efficient way to heat your swimming pool, but only if you choose the right capacity. Here’s how to properly calculate the right size so you save more (while swimming more!) in the long run.

Choosing a correctly-sized heat pump for your pool must be calculated very specifically. Heat pumps operate differently from gas pool heaters because it transfers the existing heat out of the air to warm your pool water. So, there are many variables to factor in, including:

  • The general annual average temperature of your area
  • The size of your pool
  • How many months a year you plan to heat your pool

Table of Contents

The difference in electric heat pumps.

There are two types of electric heat pumps for pools. On/off heat pumps switch off when the temperature is reached, and switch back on when the water cools.

The second type is much more energy-efficient because it’s fitted with a smart inverter that slows down or speeds up to keep the pool at the set temperature. Full inverter heat pumps automatically self-regulate their speed, which uses less power than an on/off heat pump.

Inverter pool heat pumps usually have a better COP too, which we’ll look at now before we get to the calculations.

Measuring COP and Kw.

Coefficient of Performance (COP) refers to how much energy a heat pump can produce compared to how much it consumes. The higher the COP, the more powerfully it produces heat and the lower your power bill.

For instance, a pool heat pump with only an on/off function either runs at full capacity or not at all, much like doing 100km/h down the highway, screeching to a halt and then flooring the pedal again. These heat pumps typically have a COP of around 5, which means it generates 5kw of heat for every 1kw of energy used.

Electric heat pumps with full inverter technology are the most efficient, with many having a COP over 12. We recommend these types of electric heat pumps above all others because of their efficiency, lower environmental impact and extremely quiet function.

The science behind sizing a pool heat pump.

At this point, it’s fair to say that it’s easier to have a professional size your heat pump for you because they know what they’re doing. The science behind heating your pool with the most efficiency can be daunting, and costly if you misjudge any elements.

Our team are always happy to help with heat pump sizing, and it’s something we do every single day. Just give us a call or contact us through our website and we’ll walk you through it.

Having said that, let’s look at how to size your heat pump according to your pool size.

Step 1. Calculate the size of your pool.

If you don’t already know your pool’s volume, you can work it out by measuring the length and width and multiplying it by the average depth (L x W x D). For example, a standard pool with a length of 7m and width of 3m, and an average depth of 1.3m will have a volume of 27.3 cubic metres, or 27,300 litres (7 x 3 x 1.3).

Step 2. Work out the kW required for your pool size

Once you know the capacity of your pool, you can size up a pool heat pump to suit.

Some people use a calculation of m3 ÷ 2500 to find the kW required from the heat pump, but that formula doesn’t take into account other factors and isn’t a reliable guide.

Instead, here is a very general guideline on pool capacity and heat pump sizes. Remember, pool heat pumps come in a variety of sizes and capacities depending on the brand, so these figures are to give you an idea, and are not hard-and-fast rules.

Pool Size

kW Required


Minimum 9kW


Minimum 12kW


Minimum 16kW


Minimum 16kW


If you live in cooler parts of Australia, such as Victoria, South Australia, or Tasmania, you’ll likely need to choose the higher end of the kW capacity. You could consider going up to the next size so your heat pump is more efficient.

Step 3: Consider other factors

The general rule for pool heat pumps is: the smaller the pool, the smaller the heat pump. But, if in doubt, always go a size up rather than a size down. Even if the initial outlay is a tiny bit more costly, you’ll ultimately save a lot more on your power bill – and that’s what counts most.

Other factors can impact how efficient your pool heat pump will be, for instance:

  • Each unit has a low and high COP depending on the ambient temperature and humidity, so its efficiency is determined by where you live. Colder climates may require a larger heat pump.
  • If you don’t have a pool cover, your electric heat pump will need to work harder to keep your pool warm (which is why we say it’s essential to use a pool cover, which can reduce your heating costs by up to 80%!).
  • If your pool is above ground or extremely large, keeping it at temperature will be more costly.

What you’ll need to know before calling for a quote

A pool heater expert will be able to give you the best advice to size your heat pump. They’ll factor in every element to make sure you get everything you want – pool heating for as many months of the year as you like, with the lowest operating costs possible.

So, before you call, have this information handy:

  • The size of your pool (height, width and depth or the capacity in litres)
  • The location of your pool filter pump in relation to the house
  • If you have a pool cover (if not, we strongly suggest you do!)
  • If the pool is above ground or in an extremely shady location
  • How many months of the year you’d like to swim

Please feel welcome to call us anytime for a quote on the best kind of electric heat pump for your pool. We believe pools shouldn’t go to waste for half the year – heat it and love it year-round!


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