Pool heater sizes, your complete cheat sheet on how to find your perfect fit!

Gas Heaters

Pool heater sizes, your complete cheat sheet on how to find your perfect fit!

There are a lot of steps involved when trying to work out the pool heater size you need for your pool. You need to work out the size of your pool, factor in the area’s climate, and decide how much financial investment you’re willing to provide.

There are many considerations, like the kind of pool heating you should choose, and the regulations you need to follow. Due to this, it can be tricky to decide what size pool heating system is best. Below we have outlined the key elements and methods that you can use to choose the right pool heater for you.


Firstly, it is essential to look up the climate and temperature means for your town/city. For those getting a pool heating installation in Canberra and Sydney, the mean maximum temperatures according to the BOM are 20.0°C and 21.8°C, respectively. That is reasonably warm compared to other parts of the world. But it isn’t tropical Queensland. The climate simply isn’t going to be warm enough to keep your pool at a comfortable temperature for an extended swimming season.

However, it does mean that there will be enough warmth in the air for a pool heat pump to work effectively throughout the year. Unlike gas heaters which use the thermal energy to increase the pool’s temperature, heat pumps extract thermal energy from the ambient air. This means that they require some ambient heat to be effective. Gas heaters are often used in spa/pool combos in Sydney. However, many builders and pool owners are now selecting a larger heat pump that will heat both the pool and spa instead. It’s also important to note that gas heaters are particularly difficult to source at this current point in time.  

It also helps to know what the temperature is likely to be during your desired swimming season. By knowing this, you can estimate how much assistance the sun will provide with heating. This may alter how large of a heating unit you require.

Size of Your Pool

The size of your pool directly relates to how much water you have inside it. This has implications on your pool heater size. For a rectangle pool, the formula is simple:

CBM (cubic metres) = Length multiplied by width multiplied by height (l*w*h).

This will give you the cubic meterage of your pool. From here, you multiply this by 1000. It is 1000 because there is 1000L within one cubic meter. Finally, you will have the total litres within your pool.

TOTAL LITRES = Length multiplied by width multiplied by height (l*w*h) multiplied by 1,000.

It’s the effectively same process for a circular pool. Except there are a few more calculations needed. For this, we use a special number called Pi (π). We also use half the diameter of the circle called the radius. The formula is as follows: π multiplied by the square of the radius, multiplied by the height, multiplied by 1000 (π*r2*h*1000).

If your pool, like many, is a combination of shapes leading to a pear style, you can break it up into smaller sections then add them together at the end. If you vowed never to do maths again after high school, please contact one of our friendly team members who will crunch the numbers for you.

Energy Requirements

Unfortunately, the calculations don’t finish here. Now that you have estimated how much water is in your pool, you can discover how much energy will be required to heat it.

For this, we can use an equation called the “specific heat capacity”. The specific heat capacity for a substance tells us how many kilojoules of energy are required to increase its temperature. In this case, we are looking at increasing the temperature of the water by 1°C.

Specific Heat Capacity for water = 4.196 kilojoules/litre/degree.

So, say our pool is 45,000L, and we’re coming out of winter. We need to increase the pool’s temperature by 10°C. Using the formula, we would get a huge number of kilojoules (188,370kj). This however converts to a more manageable 521kWhrs.

While this does feel very much like year 10 maths, these are the sort of calculations that you will need to use. They help us to determine exactly how much power your pool heating system will need.

Alternatively, you can chat to one of our expert staff on 0481162519 who can provide a recommendation for your situation.

Now we know how much energy we need, it’s time to think about…


At a rate of 28c per kWh assuming a 1:1 transition of energy to hot water, this initial heat up for our above example would cost about $145. However, this will differ given your situation.

However, most heaters do not operate on a 1:1 transfer of energy. Pool heat pumps, for example, can work up to a ratio between 1:6 – 1:16 with our new elite v3 range. A gas pool heater operates at around a 1:0.9 efficiency ratio, so the type of unit you choose can significantly impact your power bill. However, the different styles of pool heating units have unique characteristics which we have discussed here.

When considering costs, how much power the pool might consume is not the only factor.

The cost of the heating unit itself is something to think about. At Eclipse Pool Heating, we offer a range of Madimack and Astral heating units at different price points and sizes depending upon your needs.

It might be simple to think that if you have a big pool then you need a big heater. While this is true in some cases, a lot of the time it isn’t. You might only need to raise the temperature of your pool by a couple of degrees over summer to take the chill off.

For this example, a small/moderate sized pool heat pump would be sufficient. However, if you wanted to swim all year round in a large-sized pool with comfortably warm water, then a large gas pool heater is probably the best option.


There are a lot of steps involved when trying to work out the pool heater size you need for your pool. You need to work out the size of your pool, factor in the area’s climate, and decide how much financial investment you’re willing to provide.

Independent of your pools size, the climate, or your financial situation, Eclipse Pool Heating’s installations in Sydney and Canberra utilise a unique approach for every customer. This ensures that we find the perfect pool heater size for your needs. Speak to our expert staff today on 0481162519 or contact us through our website to find your pool heating solution.

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