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- Materials used in areas designated as non-combustible must be rated as non-combustible per NFPA 220 Standard
on Types of Building Construction, or reported as passing ASTM E 136, Standard Test Method for Behavior of
Materials in a Vertical Tube Furnace at 750 Degrees C.
WARNING: common finishing materials not approved for use:
- Paper-faced gypsum board (drywall) including Type X Fire Rated board is not a non-combustible material.
- WonderBoard brand boards are commonly used as a backerboard for tile. WonderBoard backerboard is not a non-
combustible material.
- Durock brand cement board contains a polymer coated fiberglass mesh. This can smell when heated. For this
reason Durock cement board is not approved.
Non-combustible finishing materials must be insulated from any combustible elements of the construction such as
wood framing. This can be accomplished by one of the following:
Option 1: Construct the enclosure using only non-combustible finishing materials and framing.
Use steel studs and non-combustible material to build the enclosure for the burner.
Option 2: Create an air gap behind the non-combustible finishing material by following the method shown below.
The gap between the material can be left open or insulated with mineral wool.
Method for creating an air gap behind non-combustible finishing material:
Hardibacker 500 or other non-combustible rated cement board is recommended for use in constructing the
enclosure. Do not use Durock or WonderBoard brand cement board. These boards are not rated as non-combustible
materials and will off gas or deteriorate when subjected to heat.
1. Install a ½” thick cement board to the wood framing.
2. Cut 2” wide strips of ½” thick cement board to use as spacers between the first layer of ½” thick cement board
and a second layer of ½” thick cement board. This will create an air gap between the two boards.
3. Install a second layer of cement board to the strips. The gaps between the strips can be left open or insulated
with mineral wool.
4. Install the desired non-combustible finishing material to the second layer of cement board.
- The bottom of the enclosure that holds the burner can be constructed from any construction material including
combustible materials.
- In the non-combustible area use only fasteners and adhesives that are resistant to a temperature of 300°F (150°C).
For an adhesive, High Temp 450°F silicone adhesive is recommended.
- The minimum F dimension of 14” allows for a 2” tall junction box. If a taller junction box is used increase the depth
of the cavity.
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