How to Size a Pool Heat Pump

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. But keeping your pool open during the cooler months can be expensive, and many pool owners forgo this pleasure when they see their energy bills at the end of the quarter. They can be eye-popping!

But there’s a way to heat your pool without burning a hole in your pocket – and that’s with a pool heat pump. Unlike electric or gas pool heaters, pool heat pumps harness the heat from the atmosphere to warm your pool and maintain the temperature over time. Not only does this extend your swimming season, but it can also reduce yearly running costs and cut carbon emissions. 

But with all the pool heat pumps out there, how do you know which one to buy? Does energy output matter? What size should your heat pump be? Is bigger better? In this article, we explain what pool heat pumps do, why you need to conduct a thermal audit and how to find the right size for your pool. Let’s get stuck in!

What is a pool heat pump?

Source: My Perfect Pool

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 minimising 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 factors affect pool heat pump sizing?

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

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.

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 and maintain the temperatures, and energy bills will go up accordingly. 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. 

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.

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! 

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. Please refer to our online heat pump calculator for a more precise calculation. 

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, an online calculator 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. Once you’ve weighed these up and ruled out non-contenders, you’re ready to make a purchase!

Installing a pool heat pump

Like your pool pump and filtration system, your heat pump should be installed by a pool professional. Even if you have some plumbing or electrical knowledge, don’t be tempted to do it yourself – you could void your warranty.

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? 

While pool heat pumps are cheaper than other heating methods, you’ll still see an increase in your energy bills. However, you’ll minimise these 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. 

Source: www.mytopia.com.au

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. As you can see, an electric heat pump, both with and without a cover, provides the most value. If you want to see how other pool heaters compare, check out our article on pool heating. 

Source: Complete Fibreglass Pool Kits

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.  

Bottom line

Who says you need to give up swimming during winter or even in a cool climate? 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 or heat pump calculator to find the right heat pump size for your pool. Or if you’re short on time, contact a pool technician for expert advice. Once your new pump has been installed, remember to follow our heat pump maintenance tips and use a thermal pool cover to minimise heat loss. 

Ready to buy or upgrade to a new pool heat pump? If so, contact one of our approved dealers today!