I recently moved my office to the second floor of our home and I haven't been able to get the temperature below about 78 even though the thermostat is on 72. My son's bedroom had been the same way until the other day when I removed his vent cover (diffuser) to paint the ceiling. Today I noticed his room was like a freezer, so I removed the vent cover in my office and now it is cool in here. Is this normal?
My vent cover is round and looks like this:
with the exception that mine only has two openings rather than three.
Here's my theory...when the diffuser is on, the cold air is mostly pushed out along the ceiling where the air is the hottest. This warms it up as soon as it comes out, before it has a chance to "fall" down to where I am. By removing the cover, the air is being pushed straight down, essentially cooling the air lower in the room rather than near the ceiling.
My cover is about 30 years old, so perhaps it is poorly designed?