B-Vent Safety and Combustible Clearances

I was rummaging through my inspection photos and found a couple that I thought make a good point about an often seen problem -- combustibles packed around the B-vent in the attic. Especially in older homes, time and time again, the inspector sees insulation resting in contact with the B-vent. A B-vent is the metal duct that is normally used to vent gas and propane appliances such as furnaces and water heaters. These vents can achieve temperatures of 300 degrees when gas appliances are operating. Therefore, insulation, including fiberglass, should be a couple inches away from a B-vent to eliminate the hazard of a fire. This is easily accomplished if a homeowner gets a piece of sheet metal and bends a collar or a ring of metal to fit around the vent. Tack it in place, remove all insulation between the ring and the vent, and the job is done. In a newer home, a commercially manufactured shield is often put in when the vent is installed. The photo on the right is the concern that an inspector sees frequently at an older home -- it seems to be a problem most of the time in older houses. The vent on the left is neatly done with a collar or shield made for that purpose in place. This is at a newer house. I hope this description and the photos clarify an often misunderstood, but easy to fix, concern.

Nice Job!                                       No clearance to vent!

For a chart showing recommended combustible clearances click here. For further information on B-vents and this topic, from Seattle Home Inspector Charles Buell, please click here.

Steven L. Smith

www.kingofthehouse.com