Can heating controls be fitted on radiators with covers?

January 2013

Question

Some time ago I had heating controls fitted on all the radiators in the house — ten out of 15 of the radiators have covers fitted. A while later I had a gas fitter in the house and when I mentioned to him that I was disappointed with the heating he informed me that heating controls should not be fitted on radiators with covers. Could you confirm that this is so?

Answer

Your gas fitter is correct! You don’t mention what kind of controls are fitted to your radiators but most likely these are Thermostatic Radiator Valves (TRVs) which can be set to a temperature ranging from off to full. I also assume you are referring to decorative radiator covers or cabinets made of timber or MDF and not the hard plastic packaging covers that sometimes come with TRV controls?

TRV devices rely on room air moving through them so they can assess its temperature, they then automatically open or close to allow more or less hot water to flow through the radiator to maintain the desired temperature in the room according to the setting on the TRV.

If the TRV is covered then a ‘micro climate’ is created around the valve and it responds to the warmth in the pipe and the immediate smaller space created by the cabinet rather than the relatively cooler air of the room beyond, the cover tricks the valve into thinking it’s done its job and it shuts off the hot water flowing in the radiator!

The same thing happens if the valve is covered by curtains or other objects placed against them so it is important to maintain free air around them.

If it is not possible for some reason to have this air movement directly around the TRV such as that caused by fitting a cabinet over the radiator then a remote ‘capilliary’ sensor can be fitted to replace the top of the TRV to read the room temperature elsewhere.

If the pipe work flowing to other radiators runs beneath the TRV then the hot air rising from them can also trick the TRV to think that it is warmer than the real air temperature in the room, in which case you should insulate your pipes with good quality pipe insulation.

Another thing to look for is if the TRV has been fitted correctly. Find a small arrow cast on the usually chrome fitting, this should be pointing in the direction the water in the system should flow from the boiler.

If not, then the valve will stop or slow the flow in reverse of its designed operation and the radiator can’t operate properly and you should have a plumber inspect and simply reverse the fitting.

It should be straightforward to fit remote sensors and most manufacturers have kits available, if in doubt you should consult a registered plumber or select one from the SEAI approved list to help.

Fergus Merriman is a chartered building surveyor