But someday soon I may need a new furnace and I don't know how they work.
Here is the reason: I'm getting a new burglar alarm (mine went up in smoke, literally) and my friend told me they had a built-in temp sensor, to notify them if the house temp got too low.
It turns out this model requires an add-on switch, and while trying to decide where to put it and how to wire it, it occurred to me: Why wait until the house is getting too cold. Then if I'm away, my friends only have a day or two to get there and fix the furnace and warm the place up. Why not also notify the monitoring company there is a problem when the furnace first tries to ignite and can't (no fuel, nozzle clogged, furnace broken, etc.)
My current furnace has a mechanical relay, a latching relay I presume????
and if it is not double pole or double throw, I could buy a latching relay that is, and use it instead and connect the unused pole to notify the alarm that the furnace needs resetting. I would give that its own zone, so that I would notice it even when I was home, when setting the alarm.
But I'm guessing everything is transistorized in a new furnace I buy. I don't have trouble working with IC's and circuit boards, but that doesn't mean there will be a place to connect. Is there any way to do the same thing with the new furnace? Is there a brand of furnace that would make this easier than other brands?