Q. Vent Insulation Clearance

Do I still have to use a metal shield and leave an air space around a Type B vent pipe if it is passing through a drywall ceiling and fiberglass batt attic insulation, both of which are noncombustible?

A.Mike Hamlin, an hvac contractor in Meredith, N.H., responds: The short answer is yes, because no manufacturer or code official would want to leave the decision of whether or not the air space is necessary up to an installer or home­owner. The installation instructions for the AmeriVent B-vents we typically install specifically call for a minimum one-inch clearance to both combustible materials and insulation, regardless of insulation type. In addition, the various supports and firestops provided by AmeriVent and other manufacturers are designed to ensure that this one-inch spacing is maintained around the B-vent pipe as it passes through ceiling and wall assemblies.

In general, the installation of gas piping and venting systems is governed by both the manufacturer’s installation instructions and by NFPA 54, the National Fuel Gas Code. In addition, some local codes may contain addendums to NFPA 54 requirements, in which case the more stringent rules apply, as interpreted by the local code official. In my experience, most officials go strictly by the book to avoid questions of liability, and don’t care whether the insulation is fiberglass, foam, cellulose, or something else. (Also, keep in mind that the paper backing on some types of batt insulation is flammable, even if the insulation itself is not.)