I know negative pressure in a furnace room can be a combustion/exhaust safety issue. What about positive pressure?
I have a small furnace closet, the furnace and ducting fills the closet. There is no significant leakage to equalize the pressure between the inside/outside of the furnace closet. The furnace is a newer unit, York 95% efficient, direct vented with make up air supplied to a sealed cabinet. The cabinet is the component of closed combustion, not the combustion chamber.
Ducting: The filter access is well sealed. There is no return air register in the furnace closet. But there is an open supply register that supplies air handler pressurized warm air to the furnace closet. This air from the air handler will pressurize the furnace closet.
I did not measure the pressure with a monometer, because I didn’t have it with me. This was a home inspection. I wouldn’t be surprised if there will be +30 pa or more of pressure in that room with the closet door closed and the air handler running.
There is no opening in the wall to the exterior to equalize the furnace room pressure to the ambient atmosphere pressure.
Is this a safety issue? Does it effect the operation of the furnace?
I know on the negative side, depressurization of -50 pa is the limit of this furnace. If the air handler pressurizes this room above +50 pa, is that a safety issue?
Flex pipe on the right of the image exhausts air from the air handler, supplied to a location near the floor. Cabinet on the left is open, with the exhaust vent visible.
Here’s an image of the furnace with the cover removed. Combustion air on the left, vent fan and flue on the right. Burners visible under the combustion air termination:
My report referred this to a heating contractor for follow up. I’m just curious about this condition relative to furnace operation and safety.