We recently built out an additional 600sqft theater room in our attic. It’s a big room with 14’ high vaulted ceiling. We live in Houston and room heat load is fairly high. We installed a 2-ton unit that does a good job cooling and dehumidify the room. The main house is 2250sqft with a 5 ton unit, that also does a good job cooling and dehumidifying. The systems do not share any duct work.
There is a door to the theater room, and the cold air returns for each system are in the ceiling on either side of the door.
My question is, what happens if we leave the door open?
I’d think leaving the door open would make each system less efficient, because they would no longer be a “closed loop”. I also think with the higher heat load of the room, it’s better to leave the door shut and isolate the heat to that room rather sucking the hot air into the main unit.