I decided to install a new thermostat. Supposedly the newer programmable ones can save you money in energy/fuel costs by having the room temperature set colder when you’re away at work during the day. However I work from home. Whatever. It came with a $25 rebate from the local utility, so what the heck, I installed it.

We had an old school classic round thermostat. It’s actually a Honeywell T87 series.

old thermostat

The instructions for installing a new one are pretty simple. It just says to remove the old one, label the wires according to the old thermostat, and attach those wires to the new thermostat. OK. When I take off the old thermostat and cover, there are no markings or labels for the wire. It’s only a 2 wire system, so you could just use trial and error to see if it works or not. It would probably work either way, as long as the circuit is complete (that’s how simple these old systems are). But being a geek, I whipped out my multimeter to test which wire is which.

For a 2 wire system, one is supposed to be for power (R) and the other is supposed to be for heat control (W). So I tested for voltage and continuity and tada.

labeled thermostat

Now there’s actually 3 thermostat wires (you can see the black and white one in the picture, but there’s also a red wire hiding inside the wall), so I figured I could probably use that last wire to power the thermostat, instead of relying on batteries.

Well after playing around in the basement with stack relay (which actually controls the burner), and trying out different wires, I came up empty handed. The stack control is even suitable for 3 wire usage (but as I later found out through hours of online searching, the third wire is not for power - just some auxilary fan or something). Take a look at the stack relay controls in the picture below. The thermostat wiring is in the lower left.

stack control

One good thing about the hours of online searching, I know how this sucker works (mostly).

After giving up on trying to get power to the thermostat, I just popped in a couple of batters, mounted it and voila….


(The picture is a bit fuzzy, but I wanted to show the cool blue backlight.)