Archive for November 2008

So you installed the wrong heater, thermostat, wiring… all is not lost.

I grew up in a house with no insulation and only one source of heat, which didn’t make it to most parts of the house.

When remodeling the house, I tore out the bedroom down to the dirt under the house. I propped up the roof, and removed the floor and walls, fixed the foundation, and then rebuilt it all.

I insulated it well, and then put in a small gas furnace. Gas is cheaper than electricity, I reckoned, and it definitely needs a heat source, so with effort I ran a new gas line and hooked it all up.

The pilot light alone warms the room.

Usually too much. So the furnace is unused, and an electric oil-filled space heater heats the room. What a waste.

So when building my daughter’s nursery, I opted to put in an electric heater instead, since it has off mode that’s actually off…

I roughed in the can and ran 240v wiring to it, and 24v wiring from there to another wall where I wanted the thermostat to live.

Then all the finish work was done, the drywall and the painting, and it was time to install the heater itself.

And I discovered I’d installed a line voltage heater, which needs a line voltage thermostat. And instead I had a low voltage thermostat. 24 instead of 240. Only off by a factor of 10.

Worse than having the wrong thermostat is the fact that the wiring is already done and inside the walls and there is not 240 volt electrical cable leading from the thermostat to the heater.

I googled around for a solution, and found this transformer/relay (Model RC840T-240) to connect the two.

But at first I didn’t see how it would work. A light switch has the black “hot” supply wire come in, and another one leave and go to the light, right? And the switch determines if the current stops at the switch, or continues on to the light fixture.

Well I figured the relay would work the same way… two 120 volt supply wires, a black and a red, leave the circuit box and go to the relay, and then two 120 volt wires leave the relay and go to the heater. The thermostat is also hooked up to the relay and that is basically the switch. Right?

Except the wiring diagram showed the relay had three wires, a black, red, and blue. Just three. Not four. Shouldn’t it have a black/red pair for the incoming power and a blue/something pair for the outgoing power? The way it looked, one of the supply wires still went straight to the heater.

I was confused because the heater’s manual indicated that you should use 120 volt power with a 240 volt heater; that it wouldn’t run at full power that way.

So I figured if one 120 volt wire went straight to the heater, it would always be on, but at half power, right?

By the way I e-mailed these Aube people that make the relay, and they never answered. I also e-mailed the makers of the heater, but they said it would probably work but I sure really just buy a line voltage thermostat from them instead (ignoring that it would be a hardship to rewire the finished room) and didn’t answer my question about why the relay only had three wires.

Well, I finally figured out that a 240 volt heater needing two supply wires simply won’t work at all with only one. It doesn’t run at lower power. It doesn’t run at all. The warning against using 120 volt power on a 240 volt heater is probably for some yabo that would twist both heater wires together to avoid running two wires or something.

So the relay works great, and the wiring diagram makes perfect sense given my newfound knowledge. I had to break the wiring in the attic crawlspace (which I was going to have to do no matter what, since I made the initial mistake). I put in a nice box with the relay attached and was able to use all the wiring I had put in.

My daughter’s room has heat with a programmable thermostat! I wish I had had that, growing up.

Anyway, in case any other idiot out there doesn’t realize some of these things I learned the hard way, and googles for help, perhaps this page will come up.