Heat Pump sizing 

Heat pump sizes range from roughly 6kW – 15kW, and are usually quoted at the industry standard temperatures, which is 7oC/35oC. This means a 10kW air source heat pump will deliver 10kW of heat to your home if the air temperature is 7oC and the indoor flow temperature is 35oC. 

Be it a small 6kW or large 15kW system, the size of heat pump you need for your home will ultimately depend on 3 things: 

  • Outdoor design temperature 
  • Desired room temperature 
  • Flow temperature 

Outdoor design temperature 

Air source heat pumps absorb heat from the air by passing icy-cold refrigerant liquid through heat exchanger coils. The warmer the air temperature outside, the better the heat pump will perform.  

To ensure that the heat pump can meet your home’s demand for heat all year round, heat pumps are sized based on the coldest air temperatures of the year for your area. For example, heat pumps installed in Manchester use an outdoor air temperature of around -2.6oC. 

The outdoor design temperature for your area will be taken from the MCS database – the higher the coldest temperature is, the smaller your heat pump needs to be. Unfortunately, there’s not a lot you can do to change this, since the minimum outdoor temperature will depend on where your home is located in the country. 

The only downside to this is whenever the temperature is above this ‘worst case’ air temperature, the heat pump is technically oversized for your heating demand. Other factors that weigh into the outdoor design temperature include the wind chill factor, which measures how sheltered or exposed to the elements your home is. 

Surprisingly, the vast majority of inefficient heat pump installations are actually undersized, which is a result of the UK’s inefficient housing stock and it’s general lacking of quality insulation. 

Desired room temperature 

The desired room temperature is decided by the homeowner. Typically, most people want their homes to be a warm and cosy 21oC, but lower room temperatures will require less heating, so a smaller size heat pump can be used. 

The difference between outdoor and indoor temperatures can then be used to find out the total heat loss from a property. 

Flow temperature 

The smaller the heat loss, the smaller the size heat pump required. Similarly, the larger the radiators, the lower the flow temperature. 

The flow temperature is simply the temperature water needs to be circulating around the radiators in your home to meet the desired room temperature. 

This is affected by the size of your radiators (and underfloor heating if you have it) and the level of home insulation. If the radiators are too small, the flow temperature will need to be higher to meet the desired room temperature. Similarly, the better the insulation, the slower heat can dissipate outside, and the less heating is required to meet your indoor design temperature. 

Once all these factors are established, the heat pump is sized to match both the heat demand (which is taken from the EPC) and the property’s heat loss. As a rule of thumb, a well-insulated house requires 1 kilowatt of heat for every 25m2 to be heated, whereas a poorly insulated house will heat only 10m2. 

We ensure the right size Heat Pump is installed in your house

Every home is different and that’s why the most important thing is to get a heat pump system that is sized exactly right for yours.  We undertake a full, free of charge, Home Assessment visit and produce a detailed report that will tell you exactly what you’ll require and what that will cost. 

Want to find out how much your Heat Pump will cost? 

Why not take our quick Home Survey and we’ll be able to let you know if your home is suitable for a heat pump, confirm your eligibility for the available government funding and also let you have a quote. It shouldn’t take more than a couple of minutes. Click here to get started.

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