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What Size Air Source Heat Pump do I Need for my


In general terms, the larger the house the bigger the air source heat pump needs to be. Depending on the level of heat loss, the age of the property, and room types, a 100 sqm house might need a 5KW air source heat pump. This will double to 10KW for 200 sqm houses and so on.

However, it is important to note that these figures are just a guide because there are many other factors that could affect the calculation. If you would like to know more about what size air source heat pump you will need for your home, we go into detail on this topic below.

Type of property.

The size of the air source heat pump needed for newly built homes is fairly simple to calculate, because in order to comply with building regulations in the UK, houses need to have specific levels of insulation. The level of heat loss is worked out most accurately at the design stage, and so the size of the heat pump is fairly easy to predict.

Calculating heat loss in older buildings is more difficult, and for homes that were built before the turn of the century an in-depth survey of the property is always needed prior to a heat loss assessment being completed. Key questions need to be answered about:

  • Insulation, property fabric, and heat loss
  • Size of your radiators and/or underfloor heating
  • The number of rooms in the property
  • The types of rooms and their uses
  • The desired indoor temperature for different rooms
  • Seasonal temperature fluctuations

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 typically need to be kept warmer than bedrooms, and bathrooms warmer still. So, the number and type of rooms add up to determine the amount of heat the home demands and therefore the size of the air source heat pump.

For homes in the UK, the most common sizes of heat pumps installed are 4KW, 5KW, 6KW, 8KW, 10KW, or 12KW. You can go larger if you want to, but generally it is only really needed for very large properties, shared heat pump systems, and district heating installations.

For large scale commercial properties, contact the Heat From Air team to find out how we can support you too.


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Air source heat pumps.

Air source heat pumps go through much greater fluctuations in resource temperature (air temperature), especially in more northerly climates and exposed areas, so the power output varies more than it does with ground source systems. As a typical rule, the colder the air temperature, the less power (and heat) the air source heat pump can create. But that only really comes to attrition in minus temperatures.

Variable speed compressors can operate quicker during colder weather, which helps to reduce the power loss, but heat pump designs need to account for changes in power output. Therefore, air source heat pumps are often made a bit larger than ground source. This explains why in the above example, an air source heat pump would be 5KW in a 100sqm 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. All of which we will help you with!

Outdoor design temperature.

Air source heat pumps take in heat from the air by passing extremely cold refrigerant liquid through heat exchanger coils, basically the opposite to how your typical fridge operates. Therefore, the warmer the air temperature is outside, the better the pump will work. Luckily in the UK, we don’t experience very adverse weather conditions through the winter months meaning air source heat pumps consistently work more effectively during this time of the year.

As previously mentioned, to make sure that the heat pump can meet the demand for heat in your home all year round, heat pumps are sized based on the coldest temperatures of the year for your location. So, the higher the coldest temperature the smaller your heat pump needs to be. We hope that makes sense!

Desired room temperature (the lower the temperature the better).

The desired room temperature is decided by you and your personal preferences. Normally, the majority of people want their homes to be a warm and comfortable 19-21 degrees Celsius, but lower room temperatures will need less heating, so a smaller size pump can be used.

You will already be seeing huge reductions on energy costs by using an air source heat pump so having your home at a more comfortable temperature like 21 degrees won’t feel and cost a premium like it will do with gas-fired systems.

Flow temperature.

The flow temperature is basically the temperature water needs to be circulating around your radiators in the home in order to hit the desired room temperature. This will be affected by the size of your radiators (and underfloor heating if you have it) and your level of insulation. If the radiators are too small, the flow temperature will have to be higher to reach the desired room temperature. To find out whether you can you use existing radiators with a new air source heat pump system, contact us toady.

How can I work out what size air source heat pump I need?

If you live in a new-build property, the example numbers for air source 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 us, the experts for further assistance.

Get in touch with us today to see how we can design your bespoke, energy-efficient heating system. After all, Your Green Future Starts Here!

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