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
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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