In our previous house, we had a Finished Room Over Garage that we often didn't use. So the HVAC system had a damper on the duct going to the FROG. The problem with this was that the return air was *always* pulled from the hot FROG. This meant that probably 25% of the air returning to the air handler in our attic was air from a hot space. So when it was time to replace that HVAC system, I had them install an additional damper on the return air from the FROG. it ran off the same 24v power supply, but it meant that both the supply and return air was shut off when the FROG was not in use.