How big or small is the heat pump I need?
Answer: Generally, the bigger the house the bigger the heat pump. Depending on how fast the heat escapes from the house, a 100 sq m house may need a 4kW heat pump or an 8kW pump. This doubles to 8kW or 16kW respectively for 200 sq m houses.
However, these figures must be taken with a pinch of salt. It is not a guaranteed equation, because there are many things that could affect the calculation. If you’d like to know more details about which size heat pump you need for your house, please keep reading…
Type of property
The size of heat pump for new build houses is easy to calculate, because in order to comply with building regulations in the UK, properties must have certain levels of insulation and air-tightness. The heat loss level is calculated accurately at the design stage, and therefore the size of the heat pump is relatively easy to predict.
Calculating heat loss in older properties is more challenging, and for houses without full construction information a detailed survey of the building is always required before a heat loss assessment can be undertaken.
Important questions need to be answered about:
- Insulation and construction of walls, roofs & floors
- Age and specification of windows & doors
- Ventilation rates, draught-proofing or open fireplaces
- The types of rooms and their required temperatures
- Where you are in the country – location & altitude affect winter outdoor temperatures, exposure affects heat loss rates
- Part of the survey should include determining capacity of radiators, pipes and under floor heating as these can really affect efficiency
Although the overall size of heat pump is determined by the heat loss of the whole property it is still important to consider one room at a time as temperature requirements, ventilation rates and heat loss can be very different for different rooms. A room-by-room heat loss assessment and an additional assessment of the radiator/UFH capacity in each room is essential when designing an efficient heat pump system.
For homes in the UK, we often install heat pumps which are 4kW, 5kW, 6kW, 8kW, 10kW, or 12kW sizes. We can go bigger, of course. But this is only really needed for very large properties, shared heat pump systems, and district heating installations.
Also read: Air Source Heat Pumps & Underfloor Heating: Your Guide
Type of heat pump
The size of heat pump differs depending on whether you choose a ground source heat pump or air source heat pump installation.
Ground source heat pumps
As outlined at the start of this article, a new house of roughly 100 square metres in size can install a small 4kW ground source heat pump.
If you double the size of the house, you typically double the heat load and therefore the size of the heat pump. This means that a 200 square metre house would probably demand an 8kW ground source system.
If installed correctly, the output of a ground source system is quite consistent year-round.
The amount of power produced by a heat pump is heavily influenced by the temperature of the energy resource. Soil temperatures below 1 metre depth are relatively consistent, so the output of the heat pump doesn’t vary significantly.
Air source heat pumps
Air source heat pumps experience much greater fluctuations in resource temperature (i.e. outdoor air temperature), particularly in more northerly climates and exposed locations, and generally one of three things can happen at lower outdoor temperatures. It may be the power output that drops, the flow temperature may drop and the efficiency level may drop. Sizing for “winter capacity” and a particular design heating flow temperature is important.
Variable speed compressors and modern refrigerants are some of the technical developments over the last 10 years that have improved performance and efficiency of air source heat pumps but good design and informed product selection is still very important.
How can I calculate the size of heat pump I need?
If you have a new-build property, the figures for ground source and air source heat pumps in this article will provide a relatively accurate guideline.
If you have an older property, it’s advisable to contact our heat pump installation experts for an estimate.
We can give you some ballpark figures based on information you provide, although of a full system design is the only way to calculate the precise heat pump size for any property. Every project is different, and each client has different wishes.
We provide your custom renewable heat solution, calculated effectively according to your home and needs.
Are you considering a heat pump? Contact us today for a chat with no obligation.