What do the numbers on a thermostatic radiator valve mean?

Posted in: Energy and Heating
A Thermostatic Radiator Valve set to 5

Thermostatic Radiator Valves (TRVs) are a very simple way to give you full and individual temperature control over all radiators that you have TRVs installed on.

The main benefit of them are that they will save you money on your heating bills, if used correctly.

There are numbers on the thermostatic valve and many people make the mistake of thinking that they refer to the temperature of the radiator.

This is incorrect.

Room temperature not rad temperature

The numbers on a thermostatic radiator valve refer to the temperature in the room, not the radiator. This is a common misconception, so don't worry if you weren't aware of this before.

The very point of a thermostatic radiator valve is that it can detect the temperature in the room and will let more or less hot water into the radiator accordingly.

If the room is cold, the the TRV will allow more hot water into the room to heat it up. As the room gets warmer, the TRV will restrict the amount of hot water coming into the radiator to maintain the temperature. If the room temperature starts to drop, the TRV will allow more hot water in...and so on.

Numbers & temperatures

The numbers on the valve roughly correlate to the room temperatures below. When the room drops below these temperatures, the TRV will allow hot water to flow into the radiator:

  • 0 = Off
  • * = 7°C
  • 1 = 10°C
  • 2 = 15°C
  • 3 = 20°C
  • 4 = 25°C
  • 5 = 30°C

A fully functional TRV will detect the temperature of the room and automatically adjust the amount of hot water in the radiator accordingly.

During the winter, you should really set your TRV to 2 or 3 and leave it. If you go into a room that's cold and the radiator is burning hot, leave it alone and don't turn it up to 5. Let it do it's job and allow the TRV to heat the room accordingly.

(If you're away for a long time in winter, set your TRVs to * so that the rads will come on for a short while if the temp gets below 7°C)

Use TRVs properly to save money

If you turn a TRV up to 5, basically you are telling it not to stop letting hot water into the radiator until the room reaches a very very high temperature (around 30°C). If the temperature drops below 30 degrees, water will be hot allowed into the radiator.

This is unnecessary as you rarely need the room to be that hot and it also means you lose any savings you may have otherwise made on heating bills because the hot water will be constantly flowing.

The best way to use thermostatic radiator valves is to decide on a comfortable room temperature and set the number on the TRV accordingly.

Regularly changing the settings on a TRV is not recommended and will undermine their money saving qualities, which is one of the main benefits of installing them in the first place.

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26 February 2019