Be....B-vent safe!

     A while back on an inspection I called out that there should not be insulation packed around the B-vent pipe in the attic.  Some builders think that it is only combustible materials that need to be kept away from the pipe, but the manufacturers want not just "combustible" materials kept away but also materials that could "conduct" heat to combustible materials.  This explains why rockwool insulation (which is typically not considered combustible and is often used for fire-stopping) is not supposed to be packed against the pipe---it could conduct heat to the nearby framing.  All manufacturers of B-vent type vent pipe that I am familiar with have either:  "1 inch minimum to combustibles" or "1 inch minimum to insulation" stamped right on each length of pipe.  Some types of insulation, when wet (perhaps from roof leaks of condensate from the furnace exhaust), can become corrosive to the metal pipe.  The bottom line is that b-vent chimneys need a minimum of 1" clearance from insulation and combustible materials.

The picture on the left shows insulation up against the pipe with rusting apparent where the insulation covers the pipe.  A leaking flashing kept the insulation wet where it eventually rusted the pipe.insulation around pipeinsulation around pipe

 

 

 

 

 

 

 

The picture on the right was taken two weeks later after "repairs" were made (receipt and all).smiley

     In this next picture there wasn't room to run the B-vent through the space without touching the wood framing so it was changed to single wall pipe (which itself is touching the wood) and then back to B-vent pipe.  The problem with this is that the single wall pipe would require 6" of clearance and you are not supposed to change from one type of pipe to another along the length of the B-vent pipe.bad b-vent installation

 

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

A proper vent with baffle looks more like this:proper baffle

 

 

 

 

 

 

 

Charles Buell

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Post is included in group: Property Inspection Discussion

7 Comments on Be....B-vent safe!

Good detail therer Uncle Charlie. I am going to link this to a similar blog I wrote a few weeks back. I assume that is okay, a link to it. Nice job.

02/17/2008 10:48 PM by Steven L. Smith, Bellingham, Wa. Home Inspector (King of the House Home Inspection)


yes the details matter and sometimes what is Ok isn't OK

02/17/2008 11:00 PM by Spokane Realtor - Rick Callaham (Team Quintana Real Estate)


Here is the link Charlie.

http://activerain.com/blogsview/248619/B-Vent-Safety-and

In my reports I often send clients to articles I have written that explain situations found at their prospective homes. Great to have another link to your blog that has even more detailed information for them.

02/17/2008 11:02 PM by Steven L. Smith, Bellingham, Wa. Home Inspector (King of the House Home Inspection)


Good post Charles. I do not recalling ever seeing the insulation rusting out the vent pipe in this area. But then you get more rain than we do. I have seen other types of water damage though.

02/18/2008 01:35 AM by Michael Thornton - Nashville, TN area Home Inspector (Complete Home Inspections, Inc.)


Another interesting post. I would not have thought the insulation against the pipe would have mattered either.

Sean Allen

02/18/2008 11:30 AM by International Financing Solutions


It will never cease to amaze me, the number of people that work on homes that can't take the time to read and follow installation instructions.  I know I am a better remodeling than 85% of all the other guys out there, simply because I ALWAYS read the instructions.  Even if you have installed something before, there is always a chance the specs have changed, and new rules need to be followed.

Good post sir!

06/25/2008 08:39 AM by Chris Cliff (DDIY Home Renewal)


Chris thanks for visiting---good points.

(Thanks to all you others that commented----that somehow I never got back to:)

06/25/2008 08:46 AM by Charles Buell, Seattle, WA, Home Inspector (Charles Buell Inspections.com)


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Inspector: Charles Buell, Seattle, WA, Home Inspector (Charles Buell Inspections.com)
Charles Buell, Seattle, WA, Home Inspector
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