Ok…I had a 4 year old condensing gas furnace in a combination laundry and utility room. Combustion air was taken from the exterior. Installer or homeowner cut a vent into the suction return side of the ductwork creating a strong negative pressure in the room when the door was closed. I write this up every time I see it but was wondering if it is ever OK as the furnace combustion area is sealed. Is there some limit to how much negative pressure is allowed before it overcomes the furnace door seals or is it always wrong (negative pressure pulled the room door hard closed in this instance.) Thank you
If it’s a sealed combustion unit the BPI standards is -50pa. For an individual assisted draft it would be -15pa. I don’t know at what pressure it would cause an issues with draft because I have never seen it happen with an sealed unit. Allot of them have built in safety devices to shut them down if they back draft.
Code says no, I can’t think of a single good reason to have return air in a closed furnace room, direct vented appliance or not, especially as there does not seem to be sufficient supply air given negative pressure in the room.
How on earth would return air in a mechanical laundry room be a good thing? Humid air from dryer, possibility of some kind of leak in gas pipes odors, combustion leaks.
I see it a lot but always with a dryer and or W.H. in the same room. I always call it out, always seems to get fixed.