I think the "missing link" is that there also needs to be a damper on the return for the theater. So when the supplies shut, the return shuts. When they open then everything opens. That way the volume of air is in balance. It will work since you are essentially adding a dedicated return to the system while not downsizing the others in the main basement and upstairs. Therefore the return to the theater can be closed off with no impact to the amount of feed air coming back through the existing returns.
post #271 of 595
7/30/12 at 11:15am