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I have a wood-burning stove, that is used as an auxiliary heat source in the house. There's a regular electric furnace, and adjacent to it is the stove. The warm air duct (out) from the stove connects directly to the input air duct on the electric furnace.

On the side of the stove there's a White-Rodgers thermostat, E12 5D51-035.
Looks like this:
alt text

Also attached to the stove, there's a line in, a 3-conductor grounded line with a 3-prong plug on the end - for 120V power supply. There's also a blower on the stove, which takes 120V power, and has 2 conductors - white and black. It forces the warmed air through the output duct. All the wires are meet in a junction box, and none are connected.

The wiring is like this:

alt text

How should this be wired? I don't know what is meant by "fan" and "limit". I am assuming that "fan" refers to the blower on the stove. But what is the limit? I guess I just don't understand what the thermostat is doing with 2 lines coming into/out of it.

My understanding was that a thermostat is just a heat-controlled switch. I'd expect a single line in (or out) and the thermostat would open or close the circuit depending on the temperature.

If I understood the purpose of the fan/limit thermostat, I might be able to figure out how to wire it.

EDIT: OK I read a little on the fan/limit control concept. The limit is a high-temperature safety limit, I guess.

I looked on this page and found the following diagram:
alt text

The explanation is for a Honeywell fan & limit control, but it seems similar enough to the White-Rodgers device I an using. Unfortunately, I find the explanation to be vague, and the diagram isn't helpful.

What is the yellow triangle with the #2 in it? It seems like the things labelled L1 and L2 are the wires in the line in. L1 is black (hot) I guess, and L2 would be white. So I can wire the line-in white to the white conductor on the fan. Then the line-in black (hot) goes to the fan side of the fan/limit control. Wired to which conductor? white or black? If the thermostat is a simple switch then I guess it doesn't matter. Then the other conductor (black or white) can get wired to the black line on the fan.

That leaves the limit conductors - what do I do with them? I don't have any yellow triangles on my stove, to wire those to!!

2 speed fanwith temp dealy and fan relay

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up vote 3 down vote accepted

Here's the installation manual for that thermostat: http://www.emersonclimate.com/Documents/White-Rodgers/instruction_sheets/0037-1558.pdf

You're right about L1 and L2, and about it not mattering which is which inside the thermostat housing. It is a single throw switch so its terminals are interchangeable.

The yellow triangle labeled "2" in the diagram is any device you want to turn off when the temperature gets too high. The installation manual uses an oil burner as an example of such a device. In your case you'd leave that switch unwired, unless you want to rig up a solenoid valve to douse your wood fire. :)

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Ahh, thank you. Now, a followup if I may, just for clarification: what is the default disposition of the "LIMIT" terminal? In the normal case, the circuit is closed, is that right? So when the limit trips, then that circuit opens - I guess that is how I would turn off a device like an oil burner. Right? – Cheeso Dec 9 '10 at 20:02
Also, thanks for the installation PDF. I went looking for that thing but couldn't manage to find it. My google fu failed me. – Cheeso Dec 9 '10 at 20:28
That's what I would assume too but if you're going to actually use the limit switch for something it wouldn't hurt to check it to be sure. And no problem on finding the PDF; I think I searched for just the model number and that came up. – Mike Powell Dec 10 '10 at 1:39

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