Originally posted by dash
1.The code on returns is for new construction,at least interpeted that way in your are and mine.But Travis is correct ,it should be addressed,they don't have to be ducted back ti the unit ,can be "passthru" type.If you rooms are small and there is 1" between the door and floor./carpet,that may enough already.
Test:With the system running feel the air flow close to the vent,have the wife shut the door,how much if any does it "slow Down"??
2.Call companies and ask for a load calculation as part of the estimate,I think you will find many that are willing to do that.Ask when you call not when they arrive.
Problem :Get three and one will be 1/2 ton more or less.
How's the 2.5 ton been doing in the heat of the summer,likely lacking with the addition,may have been fine before.3.5 tons sounds like to much,IMHO.
3. Assuming the original home is a pitched roof,it should be relatively easy to move the run(s),from where they are tapped in ,back to the plenum.I'd ask about it.