underfloor heating and fuse size

[cansu]

I have recently worked out that a switch on my living room wall is actually for underfloor heating which I had no idea we had. Previous owner never mentioned it! I have unscrewed the fuse trap underneath and there is no fuse inside. I would like to obviously see if it works. What size fuse should be in there??

God knows but get an electrician in first, dont fiddle with it yourself

Electric floor heating, if that's what it is, is uaually around 125W per square metre, so you could make a guess. A room 4 metres x 4 metres would be 16 sq.m so around 2,000 watts (2kW)

2000W divided by 230V (nominal voltage) is 8.7amps

Most people would fit a 13A (brown) BS1362 fuse (the same type as is used in UK 3-pin plugs)

A smaller or larger room will be proportionally less or more. Electric UFH is not supposed to be installed under fixed furniture, appliance or rugs.

If it was actually 2kW load, it would cost about 30pence per hour to run. This is possibly why the previous owner removed the fuse. Gas CH is very much cheaper to run. You will see the electricity meter flashing or spinning faster when you turn the UFH on.

There is also a possibility that the fuse was removed due to a fault, such as a nail or screw into the floor puncturing a cable. An electrician would be the person to find it. Repair of UFH is often not an economic proposition.

Thanks Piglet John. That's really helpful.