I have force air (propane furnace). I would like to upgrade to a new "smart" thermostat, but they didn't run a C (common) wire which is required for most of these units to run properly.
I do however, notice that there is a Y wire, which from my understanding is used to switch on an air conditioning compressor (which I don't have).
Since I don't have one (nor do I plan on getting one anytime in the foreseeable future), is there any reason why I couldn't just move Y over to C? Seems like I should be able too, but I just wanted to make sure that it won't somehow screw with the furnace control to not have it hooked in.
Here's a picture of the furnace board:
(on a side note, does anyone have any idea why there are also stranded wires going into R & W?!)
Best Answer
You'll want to pull a new cable
The installer who put the existing programmable thermostat in didn't pull the correct kind of cable -- they grabbed a spool of network cable and used that instead. Problem is, network cables use much thinner gauge wire than thermostat cables (22-24AWG for network cabling, 18AWG for thermostat wire), which means that the voltage drops over the cable become excessive due to the improper substitution, even with the doubled-up wires.
I would suggest pulling an 8-wire, CL2 rated, 18AWG thermostat cable at a minimum -- if you can get 10-wire, 12-wire, or 13-wire stuff, all the better to avoid having to put someone else through this chore again. The unused wires can simply be wrapped back around the cable jacket at each end.