Air Source Heat Pump Guide

How does a Heat Pump work?

Air Source Heat Pumps, in layman's terms, harvest the heat from the air. It does this by drawing air through a device similar to a car radiator which has refrigerant gas running through it. When under pressure, this forms into a liquid that is very good at absorbing heat in the nearby atmosphere.

This superheated liquid is pushed through a heat exchanger and transfers that heat energy to your pool water. How well this is done is measured by what is called a COP rating, but more on that later. So as you can see, it is not a complicated machine. When it is sized and used correctly, it will result in considerable savings on your energy bills. Fantastic!!!

What size unit will I need?

Realistically when specifying a heat pump we ascertain all the different factors that suit your application needs in order to gain the size of the unit you require.

When sizing our heat pump our listings give a suggested maximum pool size. This is given with ideal conditions for example at 28°C Ambient AIR Temp and 70% relative humidity. In most applications, we rarely see this temperature for extended periods, especially in the UK.

This also assumes a POOL temp of 26°C, our experience tells us that the pool temperature is as a general rule kept warmer than this around 28°C sometimes even higher.

So when selecting an Air Source Heat Pump for your pool it is sensible to go for at least the next size up in KW rating, this is because the actual amount of extra power used is minimal and the unit will have the extra capacity to cope with changing ambient temps and humidity, this will allow the unit to run well within its capacity so will not be under undue strain and with some of our models will over extended periods use less energy than a smaller unit.

It is a common misconception that the KW rating is the actual amount of energy used, this is not the case the KW rating of the pump is the amount of potential heating that can be called upon from the unit to see how much power the unit requires can be found on all our listings.

If you are not sure please email us and we will be happy to advise, we will need some basic information as outlined below but you can also download our helpful form here.

Pool Volume
The length, width and depth. If it's not a constant depth, an average of the shallow and deep end. The way to calculate is simply to multiply the dimensions in that order. For example: 10m x 5m x 1.2m = 60. This would be 60,000 Litres or 60m³.

Surface Area
The surface area of the pool uses the same example above, just without the depth. 10m x 5m = 50m². This is important with outdoor pools for when the cover is removed, the surface area rather than volume will determine the heat lost to the atmosphere.

Temperature
The temperature you will be operating your pool at. The normal range would be between 26-28°C but this is a personal choice. Be aware, that an Air Source Heat Pump (ASHP from now on) will heat up to approximately 30°C effectively.

Swimming Season
The season or time of the year in which the pool will be used. Most domestic pools operate between May to September. The extended season is April to October and all year round is as it suggests. However, all-year-round heat operation requires a specific type of ASHP which is rated to at least -15°C but some of the ones we sell are rated to -20°C.

Daily Use
Finally, the number of hours a day the pool will be in use and uncovered. Pools must have at least a floating solar cover to retain the heat. If left uncovered, you would use far more energy than what an ASHP would save you.

Once you have all the above information to hand, we can now begin to see what Kilowatt rating the proposed unit should be. If you are changing from an electric heater to an air source heat pump, don't match the heat pump to the kW rating in your plant room as they are not the same.

Think of the kW rating as the maximum output of the unit given to very specific environmental conditions, usually 28°C @ 60% Humidity. As we all know, these are very unlikely conditions for the UK. An electric heater will consistently apply a set temperature to the water at a constant rate, regardless of the varying outside temperature.

For example, if your pool requires 100kW of energy to maintain your temperature at X (under ideal air temperatures). Then an 18kW heat pump with a power input of 2.51kW will run for 5.6 hours to heat your pool (100/18kW). This means you would consume approximately 14kW of energy (5.6 hrs x 2.51kW). A 13kW heat pump with a power input of 1.86kW will run for 7.7 hours to heat your pool (100/13kW). This means you would consume approximately 14.3kW of energy (7.7 hrs x 1.86kW).

Whilst the energy consumption is almost the same, the larger heat pump can heat the pool nearly 30% quicker. This means that you can maximise your COP by heating during the warmest part of the day, rather than running the heat pump over a longer period when the air temperature may not be at its highest. This is why we normally advise you to over-spec your new heat pump as it would never be too much for your pool, it would simply heat your pool faster.

Why buy from us?

Since 2003 we have prided ourselves on being the largest one-stop-shop in the UK, we cater for all budgets whilst sourcing from suppliers that provide both fantastic quality products and service backup as well.

Air Source Heat Pumps are a high-ticket item and as such we have seen a lot of cheaper heat pumps influx the market over the last 3-5 years, they often have dubious features and performance & are sold by companies taking advantage of this popular market - please remember we have been doing this a long time so we offer all the best products from the best-supported suppliers at the most competitive price.... buy right first time.

For comparative purposes when making your decision the best models should have some or all of the features below. They are listed with a brief explanation of what they are and why they are needed.

Features

Inverted Motor Technology

This is a system whereby the unit can use from 20% up to 100% of its maximum output or anywhere in between to maintain the desired pool temperature.

This saves on energy and makes for a much quieter unit, it also removes the amp spike found on the start-up of cheaper units.

So always look for fully inverted motors.

R32 Refrigerant

In 2025, new legislation is coming into force to stop production or limit certain categories of refrigerants. When looking to choose a unit check it has R32 as this is now the standard that must be in units after this time.

Almost all except the larger commercial units are R32 compliant in our range.

Defrost Functions

If you need your heat pump to operate all year round look for hot gas recirculation.

Even if you intend to use the pool over an extended season, this is worth having.

Unlike some models that will have just a heated tray to stop the unit from freezing up. Gas re-circ will prevent freezing up when the water is not being heated. It will pass the hot refrigerant back around the system keeping it frost free and will not waste any energy.

Heat Exchanger

Look for a titanium exchanger as this is a lot more robust than the stainless steel or nickel-plated version. It will be more resistant to poor pool chemistry (such as low pH) and can deal with salt chlorination systems.

The latest technology is twisted tube models that give even greater surface area for the heat to be exchanged.

COP (Coefficient of Performance)

It is now time to explain the mysterious COP rating. Simply put, the COP is just a measure of how effectively the heat pump harvests the heat from the surrounding air. It does this by calculating how many kilowatts are used to operate against the number of kilowatts of heat produced.

In the UK with average temperatures of around 10-15°C, our units can produce COP ratios in the order of 5-7. This means for every one kW of energy put in, you can expect a return of between 5-7 kW of heat from the air. This is by far, more efficient than a condensing boiler.

A lot of the above are not fitted to cheaper models so if you have any doubts please email our technical team at info@poolandspacentre.co.uk so we can offer our expert advice.