Any Electricians in The House?: Installing Thermostats

Hi guys. I’m looking for some help and advice from those goodjers who are electrically inclined.

I’m trying to install programmable thermostats in my house for my baseboard heaters, and ran into some problems with the wiring. I seem to have two different wiring setups in the house for the baseboard heaters. All the heaters downstairs (3 in total) are on the one circuit breaker , while the kitchen and living room upstairs share one breaker, and the two upstairs bedrooms are on another.

When I took the original thermostats off the wall downstairs and looked inside, I saw four wires coming from the wall: 2 red and 2 black. The original thermostats had 4 wires as well: 2 red and 2 black. The wiring was setup so that 1 red from the wall went to 1 red on the thermostat, 1 red from the wall went to 1 black on thermostat, 1 black from the wall went to 1 black on the thermostat, and 1 black from the wall went to 1 red on the thermostat. The trouble I am having downstairs is that the programmable thermostats only have 2 black wires coming out them. The instruction manual for the programmable thermostats has a diagram that seems to indicate that I should splice two wires from the wall together, then put the other two into the thermostat. While I am not 100% naive in electricity, I am a little leery of doing this based on my limited experience. Any thoughts on how I might wire up the programmable thermostat?

Wait... are the switched black/red wires on the same "side" of the thermostat? I can't see why the polarity woudl matter to a simple heater so as long as the circuit is completed I guess it shouldn't matter which wire is "hot" (and since you aren't likely to be touching anything that carries the live current)

The "signal" generated by the thermostat is 12v DC. One of the wires is hot, the other is return. Depending on the type/make/model of the "load" (the heating equipment), it may or may not be OK with switched polarity. I would go with the new thermostat's instructions. There's very little chance to actually "burn" anything.

The best way to clear things up would be to try and locate on the interweb the istructions for your old termostat and see what these wires were meant to be used for.

You're probably better off going back to the store and finding a double-pole (four wire) thermostat as the model you got is a single pole.

One January I decided to change my thermostat. I went through 3 defective ones before I got one that worked. It was a tense afternoon as the house cooled off.

So kudos to you for addressing this now.

Gorilla.800.lbs wrote:

The "signal" generated by the thermostat is 12v DC. One of the wires is hot, the other is return. Depending on the type/make/model of the "load" (the heating equipment), it may or may not be OK with switched polarity. I would go with the new thermostat's instructions. There's very little chance to actually "burn" anything.

The best way to clear things up would be to try and locate on the interweb the istructions for your old termostat and see what these wires were meant to be used for.

Oh good point, I wasn't thinking of the thermostat itself... Old fashioned ones are simple mercury switches on a bimetalic strip... the new electrical ones probably care (but I'd guess there are diode in there to protect against hooking it up backwards, not for sure though!)