I have a finished basement, ground floor, and upstairs. The ground floor and basement cool nicely with the AC. The upstairs doesn't cool very well.
The returns are really just holes in the drywall- there are no ducts behind them. The ground floor has a 30"x6" return vent. The upstairs has that plus 2 15"x7" return vents. I checked last night and there does seem to be decent movement of air into the big upstairs return (one or both of the other two seemed significantly weaker).
My primary question is if it makes sense to block air behind the wall above the upstairs ducts? I'm thinking of using expanding spray foam. My reasoning is it would help seal the inside and create better suction.
I'm open to other ideas too. Since I moved in 4 years ago, I've:
- had the attic insulated
- had the ducts cleaned and sealed
- put supply register boosters on 2 upstairs bedrooms
- increased the HVAC blower fan speed