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Q.Can I use type X "fire code" gypsum board to reduce clearances to combustibles for a woodstove pipe? For example, could I attach a layer or two of gypsum board to the side or bottom of a nearby cabinet to reduce the required 18-inch clearance?

A.Don Jackson responds: No, you can't use gypsum board to reduce clearances from combustion appliances and vent pipes. You may be thinking of the use of drywall in firewalls and other fire-resistive assemblies, which are intended to slow the spread of fire, not to prevent initial combustion.

You'll need a heat shield to reduce clearances to a woodstove pipe. One of the most common is a piece of 24-gauge sheet metal, attached to the nearby wall or ceiling with standoffs so that there's a 1-inch air space behind it (see illustration, below). If properly installed, this can reduce an 18-inch single-wall pipe clearance to 9 inches overhead and 6 inches on the sides and rear, according to the IRC. You can also add a protector shield to the pipe itself.


Another option would be to upgrade to a double-wall pipe. For example, Simpson Dura-Vent (800/835-4429, makes a double-wall stainless-lined pipe that is rated for 6 inches to combustibles on the sides and 8 inches above. This is available in a black finish and might look better than a heat shield.

Most codes include a chart (see IRC Table M1306.2, for example) that lists several options in addition to the sheet-metal shield, but none of the other options is as simple. Check your local code for specifics, and make sure you look at the listed clearances for your woodstove. To have an approved installation, you've got to meet those requirements, too.

Don Jackson is editor of JLC