In general terms, the larger the home the bigger the heat pump set up that is required. Depending on the level of heat loss, the age of the property, and room types, a 3-bedroomed property of around 100 square metres might require a 5kW air source heat pump to heat it effectively. If the floor space was doubled to 200 square metres, it is fair to say the size of heat pump would need to double to 10kW.

However, it is important to note that these figures are just a guide because there are many other factors that could affect the calculation when it comes to assessing heat pump sizing. Read on to find out more about the size of air source heat pump you could potentially need for your home

Type of property

Calculating the size of an air source heat pump for newly built homes is relatively straightforward, because the level of insulation will be up to agreed level because of UK building regulations. This allows the level of heat loss to be worked out accurately, so the size of the heat pump needed is fairly easy to estimate.

Calculating heat loss in older buildings is much more difficult, because there are many different factors to take into account including levels of insulation, existing radiators or underfloor heating, size of the property, number of rooms and their uses, seasons temperature fluctuations. For home that fall into this older property category, an full survey will be required to accurately estimate heat loss levels

The number of different types of rooms has to be taken into account because some rooms require more intense heat than others. For example, living rooms and bathrooms typically need to be kept warmer than bedrooms. So, an assessment of the number and type of rooms help determine the amount of heat the home demands and therefore the size of the required air source heat pump.

The most common sizes of air source heat pumps installed in UK homes are 4kW, 5kW, 6kW, 8kW, 10kW, or 12kW. You can go larger if required, such as up to 16kW, but generally it is only really needed for very large properties (usually with 5+ bedrooms).

Heat pump sizes – how much does it matter?

Air source heat pumps are affected more by fluctuations in the temperature (air temperature) than ground source heat pumps where the ground temperature is more constant, so the power output varies more with an air source unit which has to work harder to produce the required levels of heat in the colder months.

To take into account the changes in output in the colder months, air source heat pumps are often made with larger capacities than ground source. This explains why in the above example, an air source heat pump would be 5kW in a 100 square metre house and only 4kW for a ground source heat pump. The size of your air source heat pump can depend on three main factors: outdoor design temperature, desired room temperature, and flow temperature.

Outdoor temperature

Air source heat pumps take in heat from the air by passing extremely cold refrigerant liquid through heat exchanger coils. Therefore, when the air temperature is warmer outside, the pump will not have to work as hard. To make sure that the heat pump can meet your heat requirements throughout the year, heat pumps are sized based on the coldest temperatures of the year for your location. So, the higher the coldest temperature is in your locale, generally the smaller capacity your heat pump will need to be.

Desired room temperature (the lower the temperature the better)

Desired room temperature comes down to personal preference. As a rule of thumb, a comfortable temperature in the homes is around 21 degrees centigrade, but lower room temperatures will require less heat, so a smaller and less expensive heat pump may be suitable.

Flow temperature

The flow temperature is basically the temperature water needs to be circulating around your radiators in the home in order to heat your home effectively. This will be affected by the size of your radiators (and any underfloor heating) and your level of insulation. If the radiators are too small, the flow temperature will have to be higher to heat the room to the desired temperature or you may have to use oversized radiators.

How can I work out what size air source heat pumps are suitable for me?

If you live in a new-build property, the example numbers for air heat pumps in this article will give you a fairly accurate guideline to help you determine what size air source heat pump you will need. If you have an older property, it is advisable to contact our installation experts for further assistance.

A poorly insulated property is estimated to require a heat pump unit around 1.5 times the size of heat pump that would be required for a well-insulated property. To minimise your costs you should look to insulate your property to the best level possible first to avoid having to oversize your heat pump.

For an at a glance view the following should give you a good indication of air source heat pump sizes depending on size of property and degree of insulation.

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Heat pump sizing summary

How much does heat pump size matter? The right sized heat pump system is one that will meet the heat demand for your household. While outdoor and indoor temperatures, along with other factors, will have a bearing on heat pump size, you should buy an appropriately sized heating system that enables you to get the best savings.

A small size heat pump may be adequate for a small well-insulated property, but a bigger heat pump system will be required for a poorly insulated house or one where the demand for more heat or hot water is required. Generally the bigger your home and greater your heat demand, you’ll need a heat pump installed with greater capacity, especially if you are requiring it to also heat a hot water cylinder.

How much heat you require will depend on many different factors. By discussing your heat pump need with one of our expert installers will ensure that you get the right size heat pump that is more than adequate for your needs.