A Safe Woodstove Installation: How to Use Thermal Barriers
Two low-cost approaches to woodstove installation, including metal convection barriers and insulation heat board shields.
January/February 1981
By Mother Earth News Editors
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Because the walls are lined with foil-covered fiberglass duct board, this woodstove can safely stand only 18 from the combustible barrier.
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Two low-cost approaches to safe woodstove installation:
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Every well-informed woodstove owner wants to have the safest installation possible . . . but many folks have discovered that, when they follow the recommendations for safe clearances set down by the National Fire Protection Association, they end up with their heaters smack-dab in the middle of the room. Specifically, the NFPA states that no wood-or coal-burning device should be placed less than 36 inches from an unprotected combustible surface. So, when you add three feet of clearance to about three feet of stove, and include at least a foot of base pan extension in front (for safe ash removal) ... a typical wood heater will protrude some seven feet from a wall! That amounts to a fair hunk of living space lost, and also means that your hot stove will interfere with normal traffic in the room.
There is, however, a set of NFPA stipulations which state that woodburning appliances can be safely placed closer to walls if an appropriate heat shield is protecting all combustible material. In fact, when such a protector is in place, it's possible to position your stove a mere 12 inches from a flammable barrier!
At the onset of the 1979-1980 heating season, two of MOTHER's staff members were presented with clearance problems when installing their own woodstoves, and we're sure that anyone who's even contemplating wood heat will find the approaches they took—to establish the safest possible installations while maintaining maximum living space—interesting.
METAL CONVECTION BARRIERS
By positioning a sheet-metal "guard" one inch out from a combustible surface, it's possible to significantly reduce the temperature to which the flammable wall would otherwise be subjected by a woodstove's radiant heat. The metal barrier—in this case, 24-gauge galvanized steel—is itself heated by the stove, and establishes a rising convective air flow in the space behind the sheet ... effectively cooling the back of the steel and preventing the flammable wall from becoming dangerously overheated.
Building a sheet-metal thermal barrier is very easy, but there are a few important considerations to keep in mind while planning the design. First, there must be a one- to two-inch space between the floor and the steel (to allow air to pass underneath and behind the barrier). And, of course, the lumber that braces the metal (we used 1-1/16" square stock) must be positioned vertically to avoid impeding the convective flow.
