What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
No local equivalentTRV
also thermostatic radiator valve, rad valve, smart TRV, lockshield
Effectively mandatory on new and replacement radiators outside the room holding the main thermostat. The LOCKSHIELD at the other end is a different valve doing a different job — balancing, not control.
Australia
No local equivalentthermostatic radiator valve
also TRV, hydronic valve
Present only where hydronic heating is installed, which is a minority of housing, so the component is specialist rather than standard.
United Statesyours
No local equivalent(no common term)
also TRV, thermostatic valve, zone valve
Forced air with a single thermostat is the default, so per-emitter control is unusual. A ZONE VALVE is a different device — electrically driven, controlling a whole circuit from a thermostat.
Canada
No local equivalent(no common term)
also TRV, zone valve, radiator valve
As the United States, with hydronic systems more common so TRVs appear more often than south of the border, still without a standard everyday name.
The governing standard, by market
United Kingdom
BS EN 215 / Approved Document L
Thermostatic radiator valves: requirements and test methods, and conservation of fuel and power in existing dwellings.
United States
ASHRAE Handbook — HVAC Systems and Equipment
Hydronic system control including modulating valves at terminal units.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Does turning it up make the room heat faster?
- No, and this is the most common misunderstanding about the device. A TRV is a proportional valve that senses ROOM air temperature and reduces flow as the room approaches the set point — it does not change how hot the water is or how fast the radiator delivers heat while the room is still cold. Below the set point the valve is fully open and the radiator is already doing everything it can, so turning the head from 3 to 5 changes nothing about the rate; it only raises the temperature at which the valve starts closing, which means the room ends up warmer later and uses more fuel to stay there. The correct use is to set each room to the temperature that room should hold and leave it, which is precisely the opposite of how a thermostat-style dial invites people to behave.
- Why should the room with the main thermostat have no TRV?
- Because two controls fighting over one room produce a house that never settles. The main room thermostat decides whether the boiler runs at all; a TRV in the same room decides whether that room's radiator gets flow. If the TRV closes first, the room cools, the thermostat calls for heat, and the boiler fires to serve a room whose radiator is shut — so it runs for the rest of the house while the reference room stays cold and the thermostat never satisfies. If the thermostat is satisfied first, the boiler stops regardless of what every other room wants. The convention is therefore one uncontrolled radiator in the thermostat's room, and it is why installing TRVs everywhere as an efficiency measure sometimes makes a house worse.
- Why does a TRV get stuck, and what does the fix tell you?
- Because the pin it operates sits still for months. A TRV works by a capsule expanding against a pin in the valve body, and through the summer that pin is left in one position where scale and deposits settle around it — so at the start of the heating season the head turns and the pin does not move, leaving a radiator stone cold or permanently hot. The fix is usually to take the head off and free the pin, and the fact that it works tells you the valve body is sound and the head is not at fault. It is also the argument for turning every TRV fully open for a period in summer rather than leaving them all shut, which is the opposite of what most people do when the heating goes off.