It’s a common myth that heat pumps only work with underfloor heating. The truth is that they work well on any emitter system, although you may have to increase the size of your radiators to keep your home feeling warm and cosy.

Heat pumps are considerably more efficient than other conventional central heating systems. This is because they operate at much lower temperatures, but radiators must be sized correctly so that they can distribute the same amount of heat as with a regular boiler.

Compared to conventional boilers and emitter systems that operate at around 70-80°C, heat pumps have a flow temperature (the temperature water flows around your emitter system) of around 35-50°C. This has led to a somewhat misleading term of heat pump radiators being called ‘oversized’, when in actual fact they’re accurately sized as part of the survey process.

These following factors all determine the size of radiators needed:

  • Size and shape of the room
  • Heat loss

In terms of cost, replacing your radiators for a heat pump system varies. Typical radiators can cost anywhere between £100 and £300 depending on type and style but in many cases radiators are already oversized for the room. It might also be more economical to improve your home’s insulation instead of replacing radiators. Another alternative worth looking into is underfloor heating, as it can effectively heat a room at the lower end of the flow temperature band (around 35°C), which is when the heat pump performs most efficiently.

What we do

We aim for as low a flow temperature as your property will permit. We then accurately size and specify the most suitable radiator model (usually triple convector or fan-assisted radiators) to achieve this flow temperature based on the heat loss of the room and the radiator manufacturer’s heat output rating. Alternatively, we’re happy to use your own chosen radiator type for the room and size them accordingly.

Making significant changes to your home can be a little daunting – that’s why we’re here to help. If you’d like to find out how much a heat pump system for your house will cost, send us an email at [email protected] with a brief description about your intended project and a daytime contact number. One of our Technical Account Managers will soon be in touch for a quick chat before putting together a proposal, complete with performance estimates and indicative costs.


    • Hi there Mr Arnold, thanks for your question.

      Since heat pumps come in different sizes to meet different heat demands, there isn’t really a limit on how many radiators a heat pump system can supply heat to. The size of the heat pump will depend on the diameter of pipes, how big the property is and its insulation levels. For instance, Samsung air-source heat pumps can range in size from 5kW to 16kW, but particularly large properties might have more than one air-source heat pump running at the same time to meet the large demand for heat.

      Hope this answers your question!

      Kind regards,
      Evergreen Energy

  • When its referred to requiring ‘oversized’ radiators for the room to make better use of Heat pumps lower temperature outputs, what amount of over sizing is typically required?

    For example; our living room is 27m3 (low ceiling 1850s cottage) and the radiator is 6200btu. According to the suggested calcs of room volume * 153 the radiator should be closer to 4100btu. Most of the radiators in our home are oversized in this manner.


    • Hi Ian, there is no set scale. Correctly sizing radiators to operate efficiently and be able to meet the heat requirements of each room whilst operating at lower flow temperatures is highly dependant on the heat loss of each room. It is not imperative to use specially designed “low temperature” radiators – you can use standard radiators but they would need to be bigger or you would need to have more of them. Please feel free to email us directly if you would like more information or possibly book an engineer to complete an onsite feasibility assessment.

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