Water Heater Venting

I live in Michigan (cold). I inspected a handy person renovated house today and a new water heater has been installed. The vent goes through the foundation wall and then rises two stories on the outside of the house above the roof line to vent. I know that you cannot vent a water heater as this one has been vented using single wall vent, but can one use B-vent to vent a water heater where the entire vertical length is outside in the cold? Also, if anyone knows a code reference it would be appreciated.


Are you asking if a B-vent can be outdoors?

Yes, but also givin the situation where so much of the vent is going to be exposed to the cold (approximately 25’ of vertical rise). It seems to me that the hot flue gases would cool too quickly and form condensate. The condesate would cause the vent to rust and allow condensation to flow back to the water heater (via the vent). I think! My reasoning would also lead me to conclude that the cooling of the vent gases would cause backdrafting of the flue gases at the vent hood. So my reasoning says that you cannot use exposed B-vent as I’ve described, but I’m looking for validation from others (especialy those with a plumbing/mechanical background) and any code information to back me up?


I’m not aware of anything that limits the length outside, as long as it was secured from movement, but let’s get a plumber to comment about it. A photo would help. Was there proper clearance from the eaves and house siding?

Check the manufactuer’s instructions, they will specify that in cold climates vents run up the exterior of a strucutre should to be in an insulated chase. For an example, see “Outdoor Vents” on page 20 here:


Thank you Michael - the handbook is just what I was looking for. My father is a retired mechanical inspector for the same city the house in question resides, but he’s in retirement land and I haven’t been able to reach him.

When I ran into the same issue with a B-vent running vertically for about 25’ on the exterior of a house (not enclosed in a chase), for a floor furnace, he said there is no way the city would allow this type of uninsulated installation for exactly the same resons listed in the handbook.

I wanted to make sure it also applied to water heaters and it appears it applies to all B-ventied flues, regardless of the appliance.

Thank you again,

Kevin Goff