With the temps in triple digits here in Tx, I'm more conscience of unused areas of the house being cooled. Our den is 22x24 and has two central air vents. There is a return air in the den (another in the middle of the house and one in each of the two bedrooms). There is one duct run that Ys off two the two vents. I'd like to close one vent (don't want to completely shut off the room, just put a little more AC in the other parts of the house) but wonder if that will only force all the air directed to that room, out of one vent. I know that up in the attic where the ducts are, there is a way to step down the air flow but we want to be able to easily open and close the flow. So, close one completely or both half way? And with there being a return in there, is that counter productive? If needed, and I feel like it probably is, I could cover the return air in the den.

Thank you,

Monica