Wax vs Liquid

08-12-2020

What does a TRV do?

A Thermostatic Radiator Valve (TRV) regulates the flow of water into a radiator according to its setting to control the room temperature.

How does it work?

As the room temperature changes the element contained in the valve head expands, adjusting a pin in the valve to open or close it. This maintains the room at a set temperature.

TRVs use wax or liquid sensors which expand and contract to adjust the pin in the valve. The type of material used can affect the efficiency and accuracy of the TRV.

Historically, the performance of a TRV was judged solely on its response time. Unsurprisingly, liquid was judged to be the more responsive of the two. However, modern day comparisons have taken other variables into consideration to provide a much more accurate judgement. Variables that must be considered are; hysteresis, response time, high temperature, differential pressure and accuracy.  Once all factors have been considered only then can a true assessment of the overall performance of a TRV be accurately determined.  

Hysteresis measures the ability of the valve to maintain a consistent room temperature within comfort limits.

Response time measures the ability of the TRV to respond to temperature changes within the room.

Differential pressure or force is what drives the pin and opens or closes the valve.

Benefits of wax – the original material used in TRVs

Smaller:  more compact sensor element allows much better designs for air flow

Safer: wax has anti- flammable properties

Quicker: faster response time once different temperature has been set

Reliable: uses a thermally conductive copper flake in suspension

Long-lasting: wax is less likely to leak

Consistent: greater force prevents valve sticking and ensures valve performs when commanded by the element

Benefits of liquid – a more recent alternative

Faster to detect changes in temperature

Did you know: 68% of TRVs sold in the UK use WAX

What will you choose next time?