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Can you use your radiators with a heat pump?


Heat pump

It is a common myth that heat pumps only work with underfloor heating. The truth is that they work well for all waterborne central heating systems and therefore also for radiators, although you may need to increase the size of your radiators to keep your home warm and cozy.

Heat pumps are significantly more efficient than other conventional central heating systems. This is because they run at lower temperatures. When you change the heat source - for example from an oil boiler or gas boiler to a heat pump - the temperature set for the water that is fed through the radiators therefore becomes lower. So instead of the water being around 65 degrees hot on the flow and around 50 degrees on the return, with a heat pump it will only be around 55 degrees on the flow and 35 degrees on the return.

Radiators must therefore be sized correctly so that they can distribute the same amount of heat as with an ordinary boiler.

These following factors all determine the size of radiators needed:

  • Housing type, room and Watt
  • The house's insulation


Housing type, room and Watt

Different house types require different amounts of Watts to heat the rooms. It depends on how well your home is insulated and thus how much heat loss you have to expect. A good rule of thumb is:

  • Older houses without additional insulation: m2 x 65-75 W
  • Refurbished houses: m2 x 50-55W
  • Newly built, well-insulated houses / low-energy houses: m2 x 40-45 W

M2 is the size of the individual room - i.e. length times width. Regardless of whether you need radiators for a single room or for an entire house, you must make this calculation for each individual room in the home.

Example of a calculation

You have a living room of 36 m2 and live in a refurbished 70's villa. It gives the following values:

36 x 55 W = 1.980 Watts

This means that the radiator you need to cover the living room's heating needs must have an output of 1.980 W. Whether you want one large radiator, two smaller ones or three small ones is entirely up to you. You must hit a total performance of approx. 1.980 Watts in total.


Which radiators should you choose?

All radiator manufacturers state the power/watts of the individual radiators on their website in what is called a output or output calculation. Here you can find the number of watts your radiator must produce to heat the room and can thus see the size of the radiator to be installed. You can also turn it upside down and look for the size of radiator you want and see if it provides enough for the number of watts you need. If it does not, you can consider whether to install a thicker/deeper model or type of radiator, a longer or higher version or whether you should use 2 radiators instead.

If you need to replace your radiators, we have a lot to choose from - both horizontal and vertical, benches, statement pieces and completely discreet, neutral and colored ones. You should consider whether it is worthwhile to use the old pipes and therefore have a radiator of the same size as the one you are removing. You can advantageously increase the thickness of the radiator instead of the length or height to be able to use the same pipe that way.

You can find more in-depth information on our Radaitor Guide here.



What else can you do?

Test whether your radiators are big enough for a heat pump.

A simple way to find the answer (without math) is to test your radiators. It is however wisest to do so on a cold winter's day when the radiators are most challenged.

Here's how you do it:

  • Set the supply temperature down to 45 degrees (On a new boiler you change the supply temperature on the display, and on an old boiler you change it on a thermostat)
  • At the same time, you turn aloe the radiators' thermostats all the way up to full heat

If your home is not sufficiently heated during the experiment, your existing radiators are probably not large enough to take advantage of the low temperatures from a heat pump. But this does not mean that you should abandon the idea of switching to a heat pump. Either you can replace your radiators with larger ones, or you can energy-renovate your home.


Is your home sufficiently insulated?

In order to make optimal use of the heat, your home requires good insulation. If your home has thin exterior walls, leaky windows and old doors, there is a high probability that your home is poorly insulated. In addition to providing poorer heat utilization, it also results in a lot of waste heat and ultimately a more expensive heating bill. Therefore, it is always a good idea to optimize your home's energy efficiency.


If you lack data – here are some tips for calculating the heat pump's effect.

Do you know your home's annual energy consumption? If you do not have the opportunity to read it or calculate an average for the past five years, here is a good rule of thumb. A good tip for calculating your home's energy needs:

Low-energy houses/newly built houses typically use up to 0.03 kW/m2

House built from 1980 to 1985 will approx. use 0.045 kW/M2.

A house from approx. 1950 – 77 with thin insulation and old windows use approximately 0.065 kW/m2


So, a 150 m2 house from 1980 must have a heat pump that can deliver: 0.045 x 150 = 6.75 kW.

The house therefore needs a heat pump with an effect of  6.75 kW.



Please note that if you have any doubts about your heating system, your boiler or if a switch to a heat pump is the right choice for you and your home, you should always consult a professional installer.


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