How Do Thermostatic Radiator Valves Work?

Thu 1st May 2014 - 7:58am Energy and Heating How Do Thermostatic Radiator Valves Work?
Benjamin

Benjamin Clarke

In this article, we’re going to look at thermostatic radiator valves, also known as TRVs. We’ll look at how they work and how best to use them.

So what does a thermostatic radiator valve actually do? It’s designed to automatically adjust the amount of hot water coming into a radiator according to the temperature in the room, NOT according to the temperature in the radiator, which is a common misconception we’ll come to shortly.

How TRVs operate automatically is actually really simple. The heating flow comes up from the boiler in either a copper or plastic pipe (or whatever the plumber has installed). On the pipe, there is a nut, a valve seat and a pin. The pin can move up and down within the valve, which in turn allows water into your radiator. In addition, the pin will have a rubber or a copper taper on it. If the pin is pushed down, there will be no water going into the radiator, but if it’s lifted up slightly, water will be flowing into the rad.

How does a thermostatic radiator valve automatically adjust where that pin is? On top of the pin is the thermostatic part of the radiator. This is the plastic bit that you twist with numbers on the side that correlate to how hot you want the room to be. Usually they have a responsive metal that will expand and contract as it gets hot or cold. The hotter something is the more it expands and the colder it is, the more it will contract. Similarly, other thermostatic radiator valves will use a small wax canister and that gets warm, the wax will expand and push down.

Now lets look at an alternative method, which is a TRV containing a metal coil. The metal coil sits inside the thermostatic part of the valve. According to the temperature you want in the room, you open and close the radiator valve. The whole coil and plastic bit will move slightly up or slightly down. When the room is cold, the spring will contract allowing the pin to lift up and letting hot water into the radiator, warming the radiator up and therefore warming the room up. When the room is hot, the metal spring will expand and exert pressure on the radiator pin, shutting the valve and then stopping any flow going into the radiator.

As you can see, it’s a very simple way of automating the amount of heat that goes in and out of a radiator, according to the temperature in the room. But this leads us onto the problem we’ve found of how people can use their thermostatic radiator valves incorrectly.

Imagine you go into a room and it’s cold. You feel the radiator and it’s hot. That means that the TRV knows that the room is cold and it’s got the radiator on to try and heat it up. What a lot of people will then do is look at the numbers on the side of the radiator valve, which will say for example, 3 out of 10. Because the room is cold, what people often do is turn the radiator valve up to 10 and that means it will never shut down, which defeats the purpose of having a TRV. The biggest reason to install TRVs is to save money on heating bills. So if you go into a room that is cold, the radiator is hot and the TRV is working properly and you turn it up to 10, the radiator will never shut down and you’ll never save any money.

Now you know how to get the most out of TRVs, you may be thinking of installing some or upgrading your existing ones. If so, make sure you check our fantastic range of thermostatic radiator valves where you'll find a huge variety to match your style of radiator!

The radiator featured in the main image is a Ferroli Black Curved Heated Towel Rail.

Article by Benjamin Clarke

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