When I built my house, I planned to put a Quadrafire 7100 in but now I have a really hard time justifying the $6000 cost (including installation). I am now considering making the wood framed "fireplace" look like a masonary fireplace opening and installing an alcove approved woodstove instead. I will line the "fireplace" opening with the required layers of non combustible materials and can easily maintain the required top, side and back clearances if I pull the woodstove out and onto the hearth, leaving only a portion of it actually inside the "fireplace" opening. The front clearance is what is throwing me off. The woodstove I am considering (hearthstone Heritage) calls for 16" in front of the stove. The total hearth depth from the "fireplace" opening to the front of the hearth is only 20", but the hearth raised 15" off of the floor. If I pulled the woodstove forward to get more of it out of the alcove and into the room, it will only be 8" away from the edge of the hearth....but also 15" up off of the floor. How are the stated required clearances affected by this raised hearth? Technically, if you go straight out from the stove 16", there are no combustables.....only air with a wood floor 15" below that. Thanks!
The International Residential Code (the IRC) 2009 edition, does address the raised hearth issue in that allows a reduction in the thickness of the hearth extension. Also, the IRC addresses the Hearth Extensions of Fireplace Stoves. Here are the pertinent sections:
Chapter 10, Chimneys and Fireplaces, Section R1001, Masonry Fireplaces, Page 448, IRC, R1001.9 Hearth and Hearth extensions: Masonry fireplace hearths and hearth extensions shall be constructed of concrete or masonry, supported by noncombustible materials, and reinforced to carry their own weight and all imposed loads. No combustible material shall remain against the underside of hearths and hearth extensions after construction.
R1001.9.1 Hearth thickness. The minimum thickness of fireplace hearths shall be 4 inches (102mm).
R1001.9.2 Hearth extension thickness. The minimum thickness of hearth extensions shall be 2 inches (51mm).
Exception: When the bottom of the firebox opening is raised at least 8 inches (203mm) above the top of the hearth extension, a hearth extension of not less than 3/8 inch-thick (10mm) brick, stone, tile or other approves noncombustible material is permitted.
R1001.10 Hearth extension dimensions. Hearth extensions shall extend at least 16 inches (406mm) in front of and at least 8 inches (203mm) beyond each side of the fireplace opening. Where the fireplace opening is 6 square feet (0.6m squared) or larger, the hearth extension shall extend at least 20 inches (508 mm) in front of and at least 12 inches (305mm) beyond each side of the fireplace opening.
And finally, on page 486, Section 1414 Fireplace stoves
M1414.1 General. Fireplace stoves shall be listed, labeled, and installed in accordance with the terms of the listing. Fireplace stoves shall be tested in accordance with UL 737.
M1414.2 Hearth Extensions. Hearth extensions for fireplace stoves shall be installed in accordance with the listing of the fireplace stove. The supporting structure for a heart extension for a fireplace stove shall be at the same level as the supporting structure for the fireplace unit. The hearth extension shall be readily distinguishable from the surrounding floor area.
My take on the above code requirements is that for a raised hearth installation, the thickness of the hearth extension can be reduced to 3/8 of an inch. That's probably the total thickness of ceramic tile (or other noncombustible material) set in a bed of mortar. But the size of the hearth extension is not reduced to less than 16 inches on account of a raised hearth. Also the Code makes clear that the woodstove must be installed according to the manufactures' UL listing requirements.