They do make low voltage "dampers" that are bought or placed inside your ducting that can open or close on temp. Many residential a/c companies are touting these for improved air control.
kknight Reviewed by kknight on . Theromstat to redirect 6" air in / out Like have it on a 6" duct Y that will turn a flap and direct the hot air into the room until greater than 65° then it turns the flap to direct the light air back to exhaust. Has it be done or is it commercially available? This sounds like a great protection that uses almost no electricity. Rating: 5