Below is a proposed change to the International Building Code (IBC), submitted on behalf of the Masonry Heater Association (MHA), that would add a new section to IBC Chapter 21 to specifically permit masonry heaters - see attached.

Masonry heaters, as defined in ASTM E-1602, have horizontal and downward flue channels, greater distance to combustible requirements and seismic concerns that conflict with existing provisions for masonry fireplaces. A separate section dealing specifically with the construction of masonry heaters is needed.

Specifically, a masonry heater has the following characteristics:

2117.1.1 Mass. A mass of at least 800 kg (1760 lbs.).

2117.1.2 Doors. Tight-fitting doors that are closed during the burn cycle.

2117.1.3 Wall thickness. An overall average wall thickness not exceeding 250 mm (10 in.).

2117.1.4 Surface temperature. The external surface of the masonry heater, except immediately surrounding the fuel loading door(s), does not exceed 110 degrees C (230 degrees F).

2117.1.5 Channels. The gas path through the internal heat exchange channels downstream of the firebox includes at least one 180 degree change in flow direction, usually downward, before entering the chimney. The length of the shortest single path from the firebox exit to the chimney entrance is at least twice the largest firebox dimension.

2117.1.6 Maximum flue size. The chimney flue size shall not be larger than nominal 8"x12" (200 mm x 300 mm) or 8" (200 mm) round.

2117.1.7 Within dwelling. The body of the masonry heater and its chimney shall not penetrate an exterior vertical wall of the building

2117.3 Clearance from Combustibles:

2117.3.1 Fuel-Loading Door: The fuel-loading door(s) shall have a minimum air space clearance to combustibles of 48 inches (1200 mm).

Exception: Clearances may be reduced if a listed system designed for the purpose of reducing clearance to combustibles is installed in accordance with the conditions of the listing and the manufacture's instructions.

Exception #1: Wing walls a minimum of 4 in. (100 mm) in length and a maximum of 4 in. (100 mm) in thickness and be constructed with noncombustible materials are permitted to be located at the corners of a heater for the purpose of forming a room divider. Wing walls located more than 8 in. (200 mm) from a corner of the heater shall be a minimum of 8 in. (200 mm) in length and a maximum of 4 in. (100 mm) in thickness and be constructed with noncombustible materials.

Exception #2: Clearances may be reduced if a listed system designed for the purpose of reducing clearance to combustibles is installed in accordance with the conditions of the listing and the manufacture's instructions.

2117.3.4 Firebox floor: The firebox floor shall be a minimum thickness of 4 in. (100 mm) of noncombustible material and be supported on a noncombustible foundation in accordance with Section 2113.2. The top of the firebox floor shall be a minimum 2 in. (50 mm) thick of refractory material or cast iron grating.

2117.4 Hearth Extension: The hearth extension shall be constructed in accordance with Section 2113.9.

2117.5 Cleanout Openings: Chimney flues serving masonry heaters shall have a cleanout openings in accordance with Section 2111.14. Redily accessable cleanout openings shall be provided as necessary to access and clean all chimney flues and heat exchange areas.

2117.6 Heat Exchange Channels: Heat exchange channels shall be constructed with firebrick, soapstone, or other refractory materials laid in refractory mortar, fire clay mortar, or soapstone refractory mortar with full mortar joints.

2117.7 Capping Slab: Capping slab shall be at least 57 mm (2 1/4 in.) in actual thickness above the uppermost heat exchange channels.

2117.8 Gas Slot: When required, a gas slot shall have a cross-sectional area of at least 1/30 of the firebox floor area and a height of 30 mm (1 1/4 in.).

2117.9 Shut-off Damper(s): When required one or more shut-off dampers shall be installed near the juncture of the heater and chimney or in the chimney. Each damper shall have external controls and be constructed of cast iron or steel of at least 12 gage, 2.5 mm (0.10 in.) in thickness. To reduce the possibility of toxic gases escaping into the room, the cross-sectional area of the damper's opening shall be not less than 95% of the interior cross-sectional area of the flue.

2117.10 Chimney: The chimney shall not be supported by the interior wall of the masonry heater unless specifically designed to do so. When required the chimney shall be built integrally with an exterior wythe of the heater, provided the exterior wythe is constructed of solid masonry and has a minimum thickness of 100 mm (4 in.).

2117.11 Flue sizes: Flues for masonry heaters shall be specified by the builder or the designer of the unit but shall not be larger than those specified in Section 2117.1.6.

2117.12 Chimney Connector: The chimney connector shall be accessible for inspection and cleaning. Chimney connectors shall be airtight and fitted with airtight joints. Where differential movement can take place between a heater and chimney, provision for this movement shall be made so as to maintain the integrity of the connector joints.

2117.13 Seimic Reinforcing: Seismic reinforcing shall not be required within the body of a masonry heater whose height is equal to or less than 2.5 times it's body width and where the masonry chimney serving the heater is not supported by the body of the heater. Where the masonry chimney shares a common wall with the facing of the masonry heater, the chimney portion of the structure shall be reinforced in accordance with Section 2111.1.

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