A TRV is a thermostatic radiator valve that limits the output of a radiator based on the ambient temperature in the room.  As opposed to a manual valve which you have to physically adjust, a thermostatic radiator valve or TRV is amazing because it has a built-in actuator that senses ambient temperature; opening and closing the valve automatically.

Generally, your essential thermostat will control desired room temperature, the TRV will slow down the circulation of the water in the system as the room approaches the desired temperature.  Bedrooms are a popular place for thermostatic radiator valves because a lot of people want to be cooler at night when they sleep.  If one wanted their bedroom cooler than the rest of the house, this beautiful product allows them to turn down the heat in the bedroom only, while not affecting the rest of the house.

Another room where you’ll find thermostatic radiator valves used most often is the kitchen; you’re cooking, making heat, you want the temperature to maintain a constant. This will allow the valve to turn off as the room heats up and not overheat the room. People generally want warmer bathrooms and basements.  Mind you, it can’t make a radiator hotter than the rest of the system, but it can cool it down.