Thread: B-vent chimney

I believe that I know it is not correct but I can not find where it might back me up, as to the following situation I came across during todays inspection on a new house.

A 4" b-vent chimney goes up into the attci then a 45 elbow is used and ran ove aprox 15 foot to another 45 then up and out the roof.

It seems to me that the 15 foot latteral is to long. Any help would be appreciated.

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Depends on appliance type (CAT I, CAT IV, ect.), BTUs, and the vent's rise, lateral offset and diameter. For example, see pp 27 and following here.

http://www.duravent.com/docs/instruct/shbook.pdf

IMO, these calculations are beyond the scope of a typical HI,.

Thanks, that is exactley what I needed.

Originally Posted by Brian E Kelly

It seems to me that the 15 foot latteral is to long. Any help would be appreciated.

Depends ...

From the 2006 IRC. (bold is mine)
- G2427.6.9.2 (503.6.9.2) Vent offsets. Type B and L vents sized in accordance with Item 2 or 3 of Section G2427.6.9.1 shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60-degree (1.04 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall be not greater than 75 percent of the vertical height of the vent.

Thus, 15 feet is okay as long as the vent is 20 feet or greater in height above the draft hood (20 feet height x 75% = 15 feet horizontal offset allowed).


Michael, note that is from 2002 - probably little has changed with code changes, but some may have changed. By the way, thank you for that, I saved it for my files.