Roof replacement and furnace/water heater flue pipes


Senior Member
Good morning everyone! Hope y'all are doing well. I just wanted to share something we have seen numerous times so far in the fall/winter season. If you had your roof replaced it might be a good idea to go up in the attic and make sure the flue pipes for the furnaces and water heaters are connected properly. At this point we have seen about 80% of the houses that had their roof replaced have disconnected flue pipes. I'm not trying to scare anyone but this is very dangerous, as all the combustion gases are not exiting the units properly and staying inside the attic. Please remember that carbon monoxide is heavier than air/oxygen, so it will drop down from the attic into your living space.

Just go up in the attic and look at the flue pipes. If they are disconnected you can try to put them back together by fitting one part inside the other.

Thank you and take care.


Senior Member
No problem. The one for the furnace is a 4" silver pipe that comes out of the unit and goes out the roof. For the water heaters it's a 3" silver pipe.


Platinum Member
Absolutely true! Roofers only perform an external inspection of the flue pipes. If it sorta comes out pointing to the sky, then we're good to go. Sometimes a flue pipe joint in the attic is not connected by screws or metal tape and gaps/offsets can occur.
If a water heater is in a closet, the junction on top of the gas water heater may be offset, allowing heat and gases to vent into the closet rather than up the flue. I have seen both and had them corrected.
This same incident happened with me also. The roof was damaged badly because of the snowfall at the month of December. It was not properly built and wasn't tough enough so we called the Home Quality remodeling professionals and renovated our roof with roofing shingles and made it flat and tough enough to bear any kind of heavy load.