So some background, converting from an oil to a gas furnace and was looking at adding a smart thermostat. Two things that kind of raised questions and I cant seem to find much answers too. One is the thermostat, the original one only has a red and white which seems typical, what I couldnt find an answer to is that they seemed to be connected to 12/2. Where the thermostat location almost feels like the previous owner replaced a switch with the thermostat. Another question is, where do I add the common wire in the furnace? I tried following the old wire connected to it and it doesnt look like there is a spot for a common wire or it is called something else.
So I guess my two questions are:
Why would the old thermostat wires be connected to 12/2?