View Full Version : heated 120v floor and thermostat wiring

Andrew M
08-07-2007, 02:07 PM
I installed a 120v floor warming system for tile floor. Th cost of the thermostat exceed cost of wire, so in my wisdom, I opted to not use thermostat control from manufacturer but rather use standard double pole dimplex thermostat for electric heaters. Not sure if this was good choice, so here are my questions. Can I use this? I have a red, black and ground coming from the box (12-2) The thermostat has 2 red and 2 black. The tile floor warmer has one black, one white and a ground. If I can use this configuration safetly on a 15 amp dedicated breaker (Resistance of floor warmer is 7 amps), how do I wire it?

I understand that I will not have thermostatic control of the floor. I was looking for a manual adjustment.


08-07-2007, 02:51 PM
I am not going to talk about the wiring sight unseen. But that arrangement is not the best for a floor warmer. If you put the T-stat up on the wall, you will essentially be trying to warm the whole room with the floor warmer. I would contact the manufacturer of the floor warmer to see if a "wall" thermostat is recommended or even allowed for their device.

08-07-2007, 02:57 PM
I think what you are attempting is very risky. Unless you understand what their thermostat is doing, you risk getting things too hot and burning things out - maybe including the house. It might be possible, but not something anyone here should recommend, especially since you don't indicate brand...too generic of a question. Sort of like - how high of a cliff can I jump off without getting hurt?

08-07-2007, 03:21 PM
"Resistance of 7 amps" makes no sense. If the resistance is 7 ohms, on the other hand, that means the floor warmer will draw something like 17 amps on a 120V circuit, which is pretty substantial. I suspect the reason the recommended thermostat is so expensive is that it's got provision for modulating the current to avoid sudden heating and cooling, which could crack the tile and cause other problems. I've got a similar heater in my shower, and there's a probe under there that controls the thermostat -- are you sure the recommended thermostat doesn't come with such a probe?

Spent the money and sleep well.

Andrew M
08-07-2007, 03:33 PM
tiles are on and floor done. I could not set a probe if I wanted to. I guess you are suggesting I contact manufacturer? BTW, yes it was 7 ohms

08-07-2007, 03:37 PM
I could not set a probe if I wanted to.
Sure you could. Breaking up tile and resetting it is a lot easier than it sounds. Doing it so that you don't destroy the heater wire is harder, though. :(

I guess you are suggesting I contact manufacturer?
Yup. What make/model is the heater?

Andrew M
08-07-2007, 04:22 PM
easy heat 1049 wire set in thinset.

Speedy Petey
08-07-2007, 04:28 PM
You can carefully remove the grout and set the probe in the grout line.

Most every radiant floor heat I have done has required a probe to work properly.

The programmable T-stats are crazy expensive. The correct manual ones are not that bad.

08-07-2007, 05:53 PM
Looks like the Easy Heat system requires the probe:

"Our Floor Sensor is embedded in the mortar just below your tiles, which monitors the actual floor temperature to provide you with accurate comfort levels."

Honestly, it's not that bad a job to sacrifice a tile, place the probe, and set a new tile. It's much easier if you have an accurate idea of where the wires run. I like Pete's idea of doing it in a grout line -- once again, though, you've got to know where the heating wires are to ensure you don't route out a wire while you're carving a trench to lay the probe.

08-07-2007, 07:32 PM
You have at least two possible options that I know about:

1) Place a sensor under the floor;
2) Use a regulator rather than a regular thermostat.

Depending upon how your floor is constructed (including insulation) and whether you can access the bottom, you could fasten a sensor on the bottom of the floor. In my own case, the temperature below is the same as on the surface.

In place of a thermostat that would likely seldom or never shut off, a regulator would let you only draw as much power as needed to warm the floor to whatever degree feels nice on your toes: