Thermostatic radiator valve

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A thermostatic radiator valve on position 2 (15–17 °C)
20041206 1833 1764a-Dehnstoff-Thermostatventil-800px.jpg
Section of a thermostatic radiator valve

A thermostatic radiator valve (TRV) is a self-regulating valve fitted to hot water heating system radiator, to control the temperature of a room by changing the flow of hot water to the radiator.


The classic thermostatic radiator valve contains a plug, typically made of wax (forming a wax motor), which expands or contracts with the surrounding temperature. This plug is connected to a pin which in turn is connected to a valve. The valve gradually closes as the temperature of the surrounding area increases, limiting the amount of hot water entering the radiator. This allows a maximum temperature to be set for each room.

As the valve works by sensing the temperature of the air surrounding it, it is important to ensure that it is not covered by material (such as curtains). If the controller is removed from the valve the valve turns on and the radiator will always be hot.

TRVs should not be installed in the same room where the boiler thermostat is installed. This is because in the case that the TRV set temperature is below the boiler thermostat set temperature, the TRV would shut off the radiator before the latter temperature is reached. The boiler would continue to run in an attempt to reach its thermostat set temperature, potentially heating the rest of the house to uncomfortably high levels if TRVs are not installed in every room. If both TRV and thermostat set temperatures were set equally, unpredictable behaviour may occur with both devices attempting to control the room temperature.

The replacement of a manual heating control with a TRV has been estimated to save at least 280 kilograms (620 lb) of CO2 per year.[1] They are also considerably cost-efficient, using heat only when needed, and can reduce heating bills by up to 17 percent a year.[2]

As of 2012, electronic TRVs are becoming available which use electronic temperature sensing, and frequently contain programmers so that individual radiators may be programmed for different temperatures at different times of the day. Such increased control allows even better energy and CO2 saving.[3]


Position of most Danfoss heads[4][5] Position of Caleffi heads[6] Temperature in °C Temperature in °F Recommended use[4][7]
7 44.6 Frost protection
1 12 53.6 Cellar, stairs
1 13 55.4
15 59 Laundry room
2 16 60.8 Entrance hall
2 17 62.6
18 64.4 Bedroom
19 66.2 Kitchen
3 3 20 68 Living room
21 69.8
22 71.6 Bathroom
4 23 73.4
4 24 75.2
5 26 78.8
5 28 82.4

See also[edit]

Notes and references[edit]

  1. ^ Energy Saving Trust (2011), Heating and hot water controls
  2. ^ "Archived copy". Archived from the original on 2014-03-24. Retrieved 2014-03-24.CS1 maint: archived copy as title (link)
  3. ^ OpenTRV aims to save 50% of space heating energy for typical UK home
  4. ^ a b Danfoss. "User guide - radiator thermostats" (PDF). Retrieved 19 February 2021.
  5. ^ Danfoss. "RA 2000 thermostatic sensors datasheet" (PDF). Retrieved 19 February 2021.
  6. ^ Caleffi. "Thermostatic radiator valves" (PDF). Retrieved 19 February 2021.
  7. ^ Cantonal Energy and Environment Services of French-speaking Switzerland. "Bien utiliser la vanne thermostatique" (in French). Retrieved 18 September 2016.