Code reference for b-vent support

Brian E Kelly · 04-27-2007, 07:58 AM

I know that b-vent pipe must be supported at every turn and every so many feet in a horiz. and vert. runs but I have a "contractor" telling me that when the pipe is ran along the roof line then out the run along the roof line does not need to be supported as long as the pipe is supported at both turns (90's). The typical run along the roof line is aprox 10-15' long. If anyone could get me the code reference I would be greatfull. I have a copy of Simpson Dura-Vent's installation guide and it is as clear as mud on this issue.
One other point that I found in the installation guide is that they allow the b-vent pipie to be secured with sheet metal screws as long as the screws DO NOT penitrate the inner linner. I have seen other posts as to the calling out of any screws in the bvent as improper installation so I thought I would bring this up as a FYI. New to me also and I have been in the HVAC trade for many years and have always made sure the b-vent was not screwed together. Things that make you go HMMMMMMM.

Thanks for any input.

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**Michael Thomas** · 04-27-2007, 08:18 AM

Support every 5 feet. For example, see item 11 on pp 2 here:

http://www.mtlfab.com/newcom/media/l041r.pdf

Brian E Kelly · 04-27-2007, 08:29 AM

Thomas
Thanks for the quick response. What I am looking for is the reference in the building codes. The guide for Simpson recomends 4' on vertical and laterial runs.

**Bob Harper** · 04-27-2007, 08:37 AM

For the letter of the law, it falls on the listed instructions for each brand of B-vent. Your code reference IS the listed instructions and not some code section hiding in obscurity. Section 502.6 of the IFGC simply says "All portions of vents shall be adequately supported for the design and weight of the materials employed". Part of the UL 441 listing involves a lateral joint strength test which determines the spacing of suports. This involves the 5 ft. rule because B-vent does not come in longer lengths. That means you would have at least one support on that long section. A stack of 12" sections can curve. If the vent can curve to where it loses clearance then additional support must be provided, which can mean a lot more supports that just 5ft.

Some will state spans for near horizontal as well as vertical with 45 degrees being the crossover point. However, the joints must not be strained. A sloped run of 15 feet will involve probably at least 3 pipe joints unsupported in this builder's case. Just ask him why he wants to endanger the lives of the homeowners with the vent separating. BTW, when that sloped run gets near the ridge and turns vertical, it will need to be supported in three axis: two horizontal and one vertical planes.

Most vent mfrs. will allow short screws that don't penetrate the inner liner. Howeve, these screws ideally should only be located at the joints in between the rolled beads where you aren't defeating the Dewar's Flask (Thermos bottle) insulation effect. If you screw into the side of the vent, the air inside may leak and thus lose the "dead air" space. That will cause this section of vent to run cooler allowing condensation and eventual failure. Some will allow screws as long as you silicone the screw. BTW, you may find a 3/8ths inch hole drilled through the side above a draft hood that is sealed with silicone. This may be a test hole for draft and combustion analysis. Bacharach Instruments has letters from most vent mfrs stating this is allowed within a foot or so of the draft hood but not further out. Less chance of condensation right off the appliance.

Lack of proper support is one of the biggest causes for failures and fires with Vents.