Furnace B-vent clearance from window

What is the minimum clearance from a openable window?

Thanks in advance.



Clearance above the roof line looks incorrect too.


I thought it depended on roof pitch…

B-vents within 8 feet of a vertical wall are required to extend above the next roof line.

Is there also a problem with the siding being in contact with the roof coverings?

That’s pretty typical of vinyl siding, but it should have 1.5".

These are good diagrams, but neither apply to this question. Gas appliance vents are not chimneys nor are they mechanical vents.

As Jeff said within 8 feet of a vertical wall, it must extend above the roof.


I don’t follow

It does not apply to Category I appliances.

Those diagrams you provided are for solid or liquid fuel appliances and not gas appliances.

That first diagram?

I see what you mean on the second, but the first?

Ahh, brain fart. Got it.

The vertical makes it a mute point regarding the window clearance.

One clarification, isn’t any category I with a draft induction considered a mechanical vent? You’ve left me confused.

Can you tell me the code reference number for that? I believe it’s IRC??? I’m a Realtor that just finished a 160 hour class from AHIT. and I ran across this issue today. There are 2 roofs. The B vent is on the lower roof, 3 feet away and at least 2 feet below the other roof. The city inspector says that’s ok. That you go off the roof it’s on by 2 feetc above that roof. I didn’t believe him.

Bump to bump

Found it… G2427.6.3 (503.6.4)Gas vent terminations.

A gas vent shall terminate in accordance with one of the following:

1.Gas vents that are 12 inches (305 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure G2427.6.3.

2.Gas vents that are over 12 inches (305 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally.

3.As provided for direct-vent systems in Section G2427.2.1.

4.As provided for appliances with integral vents in Section G2427.2.2.

5.As provided for mechanical draft systems in Section G2427.3.3.

The new forum search feature is very much improved!

I thought it depended on roof pitch…
Manufacturer’s installation requirements should be considered too. State and AO Smith require minimum 3 feet above roof and 2 feet oabove anything within 10 feet.