I just had a new high efficiency, 2 stage furnace installed. When it runs it makes a buzzing noise. This noise gets real loud when in the second stage. I open the filter door (about 13" by 20") and the air rushes in and the noise goes away. The contractor installed 2 new return vents upstairs, but this didn't help. I plans to install a grill/return in the ductwork right next to the filter. But, I have been advised that this is not a good idea due to being so close to my hot water heater (about 4-5 ft away). My house is small (1100 sq ft upstairs and 780 sq ft in the basement).
How can I tell if the furnace speed is set wrong, if I need more return vents, or what?
I'm concerned because the research I've been doing indicates lack of air return can cause premature mechanical issues.