My high-efficiency gas furnace is located in the laundry/furnace room, which has three doors: one to the kitchen, one to the garage, and one to outside. With the blower running, if I open the garage or kitchen doors, I can feel a definite resistance until the door is open more than about
2 inches. If I move the door to within 3/4" inch of closed, the lower pressure in the laundry room will move to toward closed position, even though these doors are heavy, solid doors.
It seems like the return duct is either too small or obstructed. Any other possibilities?
So other details, which may be helpful:
The ducts within the furnace room are sheet metal. Once they pass above the ceiling into the unconditioned attic, they are 1" duct board.
There is also a gas water heater and gas clothes dryer in the laundry room. No problems with either.
Before installing the high-efficiency furnace there were openings near the ceiling and the floor in the wall between the laundry room and the garage to provide combustion air to the old one. The new furnace gets its air directly from the outside through a dedicated pipe. So I blocked the openings to the garage to prevent cool winter air from entering the furnace room. I could unblock them, but this will not solve the problem, because even if I open the door to the garage first, I can still feel resistance when I open the kitchen door (with the garage doors to the outside closed).
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Ray