How to Choose Pool Heat Pump in The Right Size

There’s nothing like swimming in your pool all year round. It allows you to cool down in summer, warm up in winter and get regular exercise whenever you feel like it. 

Pool heat pump is the most efficient heating solution. A suitable pool heat pump can save 65% to 70% of heating capacity compared to other heating equipment.

A high-quality heat pump can keep your pool comfortable all year round – with minimal expense or fuss. But to get the most out of your heat pump, you need to get the size right. If it’s too big, you could waste your money. If it’s too small, you could overwork the unit and increase your running costs. 

Luckily, finding the right size is easy when you conduct a thermal audit. This includes measuring your pool size, location, climate, preferred temperature and frequency of use. Once you’ve got these figures, you can use our simple formula to find the right heat pump size for your pool. Or if you’re short on time, contact a pool technician for expert advice

What is a pool heat pump?

Like air conditioners and refrigerators – but in reverse – a pool heat pump uses warm air from the atmosphere to heat your pool. The process goes something like this. A fan pulls in outside air and passes it over the evaporator coil. The coil is filled with liquid refrigerant, which absorbs the heat and turns it into a gas. As the gas passes through a compressor, the heat is increased further before moving into the condenser. Once here, the gas heats your pool water as it circulates through the heat pump. When this is done, the gas moves through the condenser and turns into a liquid again, restarting the process.

Pool heat pumps should not be confused with traditional electric or gas pool heaters. These produce their own heat and are measured in British Thermal Units (BTUs) or Megajoules (MJs). Pool heat pumps, however, measure heat based on a Coefficient of Performance (COP), which is how much heat is transferred based on the units used. So, if you have a heat pump with a COP of 6, that means you get six units of heat out of the pump. In general, the higher the COP, the more efficient the heat pump will be. 

One thing to keep in mind about pool heat pumps is that they rely on the air outside being warm. If you use your pool in spring and summer, this shouldn’t be a problem. But if you use your pool during the cooler months, pool heat pumps may be less efficient and use more energy. One way of minimizing these costs is to use a thermal pool cover. Not only can it help you retain the heat in your pool, but it can also reduce evaporation and keep out environmental debris.

What to Consider When Sizing a Pool Heat Pump?

When choosing the right heat pump, it’s important to conduct a thermal audit of your pool. This means looking at various factors that determine how large or small your pump needs to be – or if you need one at all. Here’s what to check:

• Pool Size
• Pool Location
• Average Climate
• Frequency of use
• Preferred temperature
• Pool cover

Pool Size

Generally, the larger your pool, the bigger your heat pump needs to be. This ensures that your pool water is heated in less than 48 hours and that your preferred temperature will be reached or maintained while you’re swimming. Likewise, a small pool will need a smaller heat pump. However, keep in mind that a larger heater running at half speed is more energy-efficient than a small one running at full capacity!

Pool Location

If you’ve got an indoor pool, then your pool temperature isn’t as low as an outdoor pool, so you won’t need to raise the temperature by too much. The same applies to sheltered or highly shaded pools. However, if your pool is in an exposed or windy area, it’s likely to succumb to temperature and water level fluctuations, which can lower the temperature of your pool. This also means that both your heat pump and pool will take longer to heat the water, particularly if it’s not large enough.

Average Climate

Local climate can play a role in your heat pump’s effectiveness. If you live in Canberra or Tasmania, lower evening temperatures or cool winters can make your pump work harder. This means it’ll take longer to heat the water. One way to overcome this is to get a heat pump that is slightly larger than what you would normally need for your pool or to use a smaller pump and keep a cover over the pool whenever it isn’t being used.

Determine the average temperature in your location all through the coldest month you’ll be using it. Take into account additional factors such as humidity, wind chill, and nighttime temperatures. If you reside in a dry environment with strong wind speeds and low nighttime temperatures, you should invest in a bigger pool heat pump.

Frequency of use

How often you use your pool will depend on your climate and preferences. If you use it all year round, then you’ll need a heat pump that can cope with a high level of usage. Likewise, if it’s only used for four or so months – and during the warmer months – you may only need a small unit to bridge that temperature gap.

Preferred temperature

Most people love swimming in cool water, particularly in summer, so your heating needs during that may be minimal. However, if you live in a cold climate or you want to swim in winter, you’ll need to increase the temperature of your water. Ideal temperatures for swimming are 24–28 degrees Celsius. If you have seniors in your household, you may want to increase this to 30 degrees Celsius. That’s because older people can be sensitive to extreme temperatures, or they may have arthritic conditions that make it difficult for them to move easily. Higher temperatures, on the other hand, can make them feel more comfortable, keep their muscles warm and prevent cramping. 

Note: Unless you live in a tropical climate and use a solar blanket, most unheated pools can be too cold to swim in. For example, an unheated pool in Sydney could be 18–22 degrees Celsius, even in summer, which is below the ideal temperatures for swimming.

Pool cover

It’s essential to have a sun cover. The outer layer of the pool water is where the majority of the heat evaporates. Covers retain the temperature, allowing you to use a smaller pump relatively less frequently. They also prevent water from escaping, reducing the amount spent on pool maintenance. You might need a pool heat pump in a different size if you don’t have a cover for your pool.

Guide to sizing your pool heat pump

Whether you’re buying your first pool heat pump or replacing an old one, here’s your four-step guide to sizing a pool heat pump.

Step 1: Measure the volume of your pool

 

 

If you don’t already have this figure on hand, pull out your measuring tape and measure the length and width of your pool. Multiply both to get the surface area of your pool. Then, multiply the area by the depth of your pool to get the volume. So, if your pool is 4 x 6 metres and has an average depth of 1.5 metres, then the volume would be 4 m x 6 m x 1.5 m = 36 cubic metres. Since there are 1000 litres in a cubic metre, this means that your pool has a capacity of 36,000 litres (36 cubic metres x 1000 litres).

Step 2: Calculate the kilowatts required to run your heat pump

Now that you’ve got your pool volume, you need to find the power needed for your heat pump to warm your pool. To calculate this, divide your pool volume by a conversion factor of 2500. Using the example above, this would be 36,000 L /2,500 = 14 kW. If you can’t find a heat pump that matches this size exactly, choose one that’s closest to that figure – but round up instead of down. More power is better than less!

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.

As a reference, the table below shows equivalencies between different swimming pool heat pumps and water temperature increases per hour according to the pool’s water volume:

For example, an 8KW swimming pool heat pump will raise the heat in a 10,000L pool by 0.58 ºC per hour. On the other end of the spectrum, a 36KW heat pump will raise a 10,000L pool’s temperature by 2.64 ºC per hour.

Pool Capacity	8 kW	12 kW	18 Kw	25 Kw	36 kW
10,000L	0.58	0.89	1.33	1.96	2.64
20,000L	0.28	0.45	0.65	0.98	1.31
30,000L	0.21	0.28	0.45	0.67	0.89
40,000L	0.16	0.23	0.34	0.48	0.67
50,000L	0.13	0.19	0.27	0.38	0.54
60,000L	0.11	0.15	0.21	0.33	0.45
70,000L	0.08	0.13	0.19	0.28	0.38
80,000L	0.07	0.11	0.16	0.25	0.33
90,000L	0.07	0.10	0.15	0.22	0.29
100,000L	0.06	0.09	0.131	0.20	0.26
120,000L	0.05	0.07	0.11	0.16	0.22

Please note: These recommendations are a guide only. The heater sizes recommendations are based on average or usual weather, soil and shade conditions. Temperature loss and heat up time will vary according to the month of the year, quality of cover if installed, soil condition, shade, wind and weather conditions.

Pool Capacity	Sydney	Melbourne	Brisbane	Adelaide	Perth	Canberra	Hobart
20,000L	9-13 kW	13 kW	9-13 kW	13 kW	9-13 kW	13 kW	13 kW
40,000L	13 kW	20-21kW	9-13 kW	16-17 kW	16-17 kW	20-21kW	20-21kW
60,000L	20-21 kW	28 kW	13-17 kW	24-28 kW	21-24 kW	28 kW	28 kW
80,000L	24-28 kW	35 kW	20-21kW	35 kW	28 kW	35 kW	35 kW

Note: Please be aware that there are many variables the heat pump can be operating, therefore, this calculation is for a quick reference only and is for extending the season with a pool cover.

Step 3: If necessary, use an online calculator

Dimensions and volume aren’t always enough to choose the right pump for your pool. As we mentioned earlier, other factors contribute to sizing, such as pool location, preferred temperature and usage. To include these factors, you’ll need to use an online heat pump calculator. This will factor in local information and preferences and provide more accurate recommendations. If you find ‌this calculator isn’t detailed enough or you want a second opinion, contact a pool professional for a full thermal audit of your pool.

Step 4: Narrow down your selection

Whether you use our simple formula or advice from a pool technician, you’ll now have a few heat pump options to choose from. So how do you narrow it down? Well, start by comparing each pump’s features against your needs and budget, such as the speed with which water heats up (this can be anywhere between 24 and 48 hours, depending on local factors), the COP (the higher the ratio, the lower your running costs), frost protection, noise levels, Wi-Fi capability and price.

Installing a pool heat pump

Generally, pool heat pumps should be placed in an outdoor location close to your filtration system. Make sure there’s good airflow and that there are no obstacles around the fan. If possible, ask your technician to install a bypass valve between the filter and the heat pump so you can still use the filtration system when the heat pump is not in use.

Once it’s installed, set the temperature and turn on the pump to activate heating. The heat pump will only start working once it can detect water from the pump going through the unit. When the desired temperature is reached, the heat will ensure that the temperature is maintained – no more, no less! 

Unlike electric or gas heaters, it may take a couple of days for your water to heat up, particularly if you’re using it for the first time or reopening your pool after winter. But once you’ve got the water up to your desired temperature, maintaining it is a cinch.

How to maintain your pool heat pump

Once you set your preferred temperature, pool heat pumps require little maintenance. There are just a few things to look out for. First, check the air intake of the heat pump to make sure it’s clear. Sticks, leaves or other debris can block this area, reducing your unit’s effectiveness and increasing your energy bills. Remove visible debris with gloves or a vacuum cleaner.

Second, inspect the water inlets and outlets. If you see water pooled around them, it could be one of two things: condensation or a leak. Test the moisture with chlorine strips to see if it’s pool water. If there’s no chlorine, it’s the former, so you’re in the clear. Condensation is common on pool heat pumps and is nothing to worry about. If you get a chlorine reading, then there might be an issue. To correctly identify the source, contact a pool technician. 

Third, if you find that your pool water isn’t warm enough, check the thermostat to make sure the setting is correct. If it is, then you might have low water flow. This could be due to a blocked pool filter. To fix this, clean any debris from the filter. This should increase the water flow to your heat pump and raise the temperature of your pool water. 

Last, get your pool heat pump checked yearly by a pool professional. An expert can find hidden issues, check the refrigeration system and clean the unit to improve its efficiency. 

Pro Tip: If you run your heat pump above 28 degrees Celsius, particularly during winter, algae and bacteria can reproduce at exponential rates. This can eat up your sanitiser pretty quickly and result in green pool water. To avoid this, shock your pool more often or lower the temperature.

Do I need to use a pool cover with my heat pump?

You’ll reduce the heating costs by pairing your heat pump with a thermal pool cover. Not only will your pool retain more heat, but your pump won’t have to work as hard to reach your desired temperature each day.

Sun + water = evaporation. Utilising your pool cover whenever your pool isn’t in use will reduce evaporation significantly, as it stops excess heat from reaching the water. With your pool retaining as much of its water as it can, this will help reduce your water bill as well as the time it takes to refill the pool.

*an average 30 m2 pool

To find out how much you can save by using a pool cover with your pool heat pump, below is a chart that compares average annual running costs for different types of pool heaters – and the difference that a pool cover can make.

40,000L pool heated to 28 degrees Oct & Apr	Gas heater annual running cost		Heat pump annual running cost
Pool Type	With pool cover	Without pool cover	With pool cover	Without pool cover
Sydney	$1101	$2201	$805	$1341
Melbourne	$1671	$3434	$1222	$2037
Brisbane	$649	$1301	$475	$793
Adelaide	$1129	$2258	$915	$1526
Perth	$1029	$2058	$816	$1361

 

Please note: These pricing recommendations are a guide only. The heater sizes and operation costs recommendations are based on average or usual weather, soil and shade conditions. Temperature loss and heat up time will vary according to the month of the year, quality of cover if installed, soil condition, shade, wind and weather conditions.