bridgeman, the furnace in our house isn't a "high efficiency" one, so it needs a supply from outside already for fresh air. I doubled up the screen on the outside vent, and put a doubled up screen where it comes to the inside as well. I would do something similar for the theater.

Serenity_Now, for future resale, you might want some type of heating in the theater, just plan on never needing to run it. To date we have NEVER had the vents open in the theater when the heat is running. Even in a cooler basement when the door has been open and the temp is a touch cool. Fire up the projector, put some 3500 BTU/hour people in there, and you don't need heat. But having it for whenever the day comes to sell, or even if you get an appraisal, most places count finished square footage based on a couple of factors, including a heat source (they don't care about A/C oddly enough) in each living space.

Farewell - June 4, 2020