/diy/ - Do It Yourself

house from the 50s has had different wiring over the decades and now im trying to organize and rewire it cleaner:
theres two wires going into a hole in the basement ceiling, one original nylon sheathed cable, and one newer 18ga to to the furnace
the nylon cable now goes to recently added transformer (I assume 24, but could be 16) that seems to feed off to the front and rear doorbells(?)
so the furnace is powering the thermostat, the old nylon wire is going the door chime, correct?