I have an outdoor wood boiler that will be providing heat to the home (via a coil in the plenum) and an existing A/C system with it's own thermostat. I have installed an additional thermostat to be used to control the fan only circuit on the current system. Simply stated I took the Red (Power) and White (Heat) wires from the new thermostat and hooked them to the Red (Power) and Green (Fan) terminals, respectively. My problem occurs when the new thermostat is used the fan runs, but so does the A/C. I determined that the existing thermostat has an internal jumper connecting the Green (Fan) and Yellow (A/C) - I don't see a way to disconnect. I know I can run the new thermostat White (Heat) wire directly to the Green (Fan) wire (not connecting it to the existing thermostat terminal). Is there anyway to hook up the thermostat without having to rewire the system when I want to switch from A/C to Heat? Are there thermostats out there that are made for this type of configuration?