Gas Vent Height

This has probably been asked and answered before, but I can’t find it, so here goes:
IRC Ch, 18 (M1804.2.4) says L vent height must be min. 2’ above roof.
IRC Ch, 24 (Table G2427.6.4) says a gas vent could be 1’ above the roof if the roof pitch is flat to 6/12 (assuming there is nothing higher within 10 feet).

Would this mean that if the L vent is for an oil burning (or pellet burning) appliance, it must be at least 2’ above the roof’, but if it is being used with a gas appliance, it could be just 1’ depending on the roof pitch?

1 Like

You do realize you are mixing gas fuel appliance vent and solid fuel burning vent together. I recommend you take some HVAC classes.

L-vent is basically a B-vent with a better interior liner and is rated for higher operating temperatures and also for both oil and natural gas appliances according to nachi:

So technically you can use an L-vent on a B-vent appliance but not a B-vent on an L-vent appliance. The problem is why would you want to if L-vents on paper should cost more based on materials?

See above: L-vent manufacturer says you can use it on B-vent appliances.

If you are using that L-vent on a B-vent gas appliance, I don’t see why you can’t use the 1 foot height above roof clearance.

If you are in an area using predominantly gas appliances nowadays but have some older oil appliances left to service, I guess I can see a potential scenario where a supply house could have ran out of B-vents due to supply chain problems and only had L-vents left in stock. A contractor then grabbed an L-vent and put it on a gas furnace, especially if this was for a new construction and builder is not going to wait for the B vents to be back in stock and have to push back closing.


Hi Martin, I have taken a few HVAC courses. L vent can also be used for natural gas appliances although it usually isn’t since it is more expensive with its stainless steel inner liner. That’s why I worded my question the way I did.

I think the problem is you don’t understand how high to run the vent. Your question was about the height of the vent not the material used for the appliance. If you are going to run L vent for a gas fired appliance you need to run it for the height required for a gas fired appliance. If you are going to run the L vent for a solid fuel appliance you will need to run it for the height required for a solid fuel appliance. The fact that you are running L vent for both appliances makes no difference. This is why I recommended you take the HVAC course. A similar question comes up every few months so it must be difficult to understand. Wait until you run into cat 3 and the flue can grade up or can grade down :slightly_smiling_face:

1 Like