by ericmark »
Sun Nov 03, 2019 9:30 pm
You do not say if wet or electric under floor heating, with wet the thermostat opens the zone valve and the temperature of the floor is controlled by pumping water from return back to feed so water not over around 35 deg C, so the on/off is a separate thermostat to the floor temperature.
With electric the floor is limited to around 27 deg C, there are two completely different methods, Raychem is a special chemical impregnated core which auto controls floor temperature, the warmed the floor gets the higher the resistance of the cable. But the other method uses a simple resistance cable and to ensure it does not go over temperature there is a pocket between the elements and a sensor measures the floor temperature, so the thermostat is a special, one it works with a higher current to most central heating thermostats, and two it has two sensors one for room temperature and one for floor temperature.
I have not seen an electric underfloor heating thermostat that does not need a neutral, however there may be one I am unaware of, and unless using Raychem then Line in, Line out, Neutral, and two sensor wires at least.
With a bathroom often a more expensive type is used with two sensors, one under floor and one air so the thermostat can be mounted outside of the room, there are also problems with earthing, some systems need an earth mat over the heating wires when used in a bathroom.
I no longer have a house with under floor heating, and to be frank when I did it was rather useless, to install the first job was dig up floor and lay a rather thick layer of polystyrene, so that the heat would not be lost, net result even with floor switched off it stayed reasonable warm.
Idea was to dry the floor, mother was an amputee, only one leg, so did not want her to slip on the wet room floor, as soon as shower turned on it cooled the floor, so from turning shower off to having dry floor was 1/2 hour minimum with extractor running as well, she was not going to wait that long before leaving the shower.
Using a simple mop did a better job, but also floor very slow reheating, before fully up to temperature it took an hour or more, and without towel rail the wet room was rather cold with the extractor running which was drawing in cold air from the hall.
The under floor sensor failed, it should have be able to be replaced, pulling it out of pocket and fitting new, but it stuck, I used the thermostat without the sensor, and to be frank the floor never got that warm even without it, could still walk on floor even if I forgot to turn it off.
Son has under floor heating, but that is more to cool the rayburn cooker than to heat bedrooms, needs a heat sink to keep boiler in cooker cool.
The wet type does work, it can't over heat, and it holds the heat for a long time, so with oil boilers it reduces the hysteresis, not been in a house with Raychem that is rather expensive, but the simple wires is not very good even if everything is A1.
