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407 lines
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<h1>Residential Wood Stove Installation</h1>
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<div style="text-align: center;">
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<a href="/"><img class="epic" src="/icons/chads/chad.png"></a>
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</div>
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<hr>
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<p class="nav"><span class="nav-left">Listed under <a href="/practical-skills.html">Practical Skills</a>.</span><span class="nav-right"><a href="/theme.html">Theme</a></span></p>
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<p>From the <a href="https://www.extension.purdue.edu/extmedia/fnr/FNR-100.html" target="_blank">original article</a>.</p>
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<p>
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Wood, when readily available, is a cheap source of home
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fuel. Unfortunately, house fires can occur when stoves are improperly
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installed or carelessly operated and maintained.
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</p><p>
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This publication, using National Fire Prevention Association (NFPA)
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standards, describes proper installation of radiant-type
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wood-burning room heaters in residential homes. These standards are
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the basis of many building codes. Recommendations will vary for
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furnaces, circulating stoves, cook stoves, and ranges. In all cases,
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you should consult local officials for details and use good sense
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during stove installation, operation, and maintenance. Some states
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recommend that you consult the fire marshall and your insurance agent
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as well as the local building permit office before installing a
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stove.
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</p><p>
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Most fires are caused when combustibles are too close to a hot
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stove, by the escape of hot gases or flames through a crack in a
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chimney, by conduction of heat from the stovepipe or stove to
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combustible material, or by sparks or coals escaping from a stove.
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Protection must be provided for combustible wall, ceiling, and floor
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materials near the stove and stovepipe as well as where the
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stovepipe passes through or near combustible walls, ceilings, and
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other materials.
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</p>
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<h2>Wall Protection
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</h2>
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<p> Stoves and stovepipes must be spaced out from walls and other
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combustible materials to prevent ignition. They should not be
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installed in alcoves, closets, or similar areas. Table 1 shows the
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minimum clearances from combustible walls and ceilings. Wood frame
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walls covered with dry wall are considered combustible.
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</p><p>
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If no wall protection is used, the common radiant-type stove or
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heater must be spaced out at least 36 inches from the wall. This
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distance may be reduced considerably if asbestos millboard and/or 28
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gage sheet metal is used for wall protection. A 1-inch or wider air
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gap between the wall and the asbestos millboard or metal panel must
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be provided. The one-inch spacers must be of a non-combustible
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material. In addition, a 1 1/3 inch or wider air gap is needed at
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the bottom of the asbestos millboard or metal panel. Circulating air
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will cool the panel and wall behind it (Figure 1). At least 36
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inches of clearance must be allowed between the top of a stove and
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an unprotected ceiling. Brick or stone provide little or no protection
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for a combustible wall since they are good conductors of
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heat. Therefore, by themselves, these are not suitable as wall
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protectors. When used, however, they, too, should be spaced out from
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the wall with a gap at the bottom to provide air circulation.
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</p><p>
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There is a simple test that will tell if you have provided enough
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clearance. Place your hand on the closest surface. If you can keep
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your hand there comfortably while the stove is operating, the
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location passes the test. If not, you need added protection.
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</p>
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<h2>Table 1. Minimum clearances from combustible walls and ceilings.*
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</h2>
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<pre>
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Stove type
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Type of protection Radiant Circulating Stovepipe
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--------------------------------------------------
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None 36" 12" 18"
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1/4" asbestos millboard,
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spaced out 1" 18" 6" 12"
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28 gage sheet metal,
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spaced out 1" 12" 4" 9"
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28 gage sheet metal on
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1/8". asbestos millboard,
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spaced out 1" 12" 4" 9"
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--------------------------------------------------
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*From National Fire Protection Association No. 89M, 1976.
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</pre>
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<a href="/files/wood-stove-1.gif" target="_blank"><img class="center" src="/files/wood-stove-1.gif"></a>
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<p class="c">
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Figure 1. Air circulation behind any type of wall
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protection is essential for cooling.
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</p>
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<h2>Floor Protection
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</h2>
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<p> All floors on which stoves are set, except concrete, must be
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protected from the heat of both the fire and hot coals falling out
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when the fuel is added (Figure 2). The NFPA recommends covering the
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floor beneath the stove with No. 24 gage or thicker sheet metal. Metal
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with asbestos backing and asbestos millboard can also be used. If
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slate, brick, etc. are used, they must be mortared in place with no
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gaps. Metal or asbestos millboard must be installed between the
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brick (slate or stone) and the floor.
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</p><p>
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If the stove legs provide less than 6 inches of clearance, 2 to 4
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inches of hollow masonry laid to pro- vide air circulation with a
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sheet of 24 gage sheet metal between the floor and the masonry is
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recommended. Eight- to ten-inch legs will provide more air space, and
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less heat will be transferred to the floor. A 2-inch layer of sand or
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ashes laid in the bottom of the stove will also help prevent
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overheating of the floor.
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</p><p>
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The materials used to protect the floor should extend 12 inches
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beyond the sides of the stove without openings and 18 inches beyond
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the side with the door or other potential openings.
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</p>
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<a href="/files/wood-stove-2.gif" target="_blank"><img class="center" src="/files/wood-stove-2.gif"></a>
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<p class="c">
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Figure 2. Clearances far stove and stovepipe from walls and floor.
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</p>
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<h2>Other Combustibles
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</h2>
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<p> Other combustible materials such as firewood, paper, curtains, and
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plastics should be kept at least 36 inches from the stove.
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</p>
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<h2>Stovepipes
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</h2>
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<p> Like fireplaces, wood-burning stoves must be vented to the outside
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of the building. A stovepipe is used to connect the stove to a masonry
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chimney or prefabricated metal chimney. The stovepipe is sometimes
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referred to as a connector. Single wall 24-gage or thicker
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corrosion-resistant steel stovepipe is recommended. If the stovepipe
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diameter is over 10 inches, a heavier gage metal must be used. The
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diameter of the stovepipe shall be the same diameter as the firebox
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outlet. In some situations, a prefabricated or insulated metal
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chimney may be connected directly to the stove. Table 2 shows common
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chimney capacities required for different sized stoves.
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</p>
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<h2>Table 2. Chimney capacity required by stove size. *
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Area in square inches of flue
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</h2>
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<pre>
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19 28 38 50 78 113
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Total flue Combined input rating of stoves in
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height in feet thousands of BTU/hr
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------------------------------------------------
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6 45 71 102 142 245 NR
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8 52 81 118 162 277 405
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10 56 89 129 175 300 450
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15 66 105 150 210 360 540
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20 74 120 170 240 415 640
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NR means not recommended
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--------------------------------------------------
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*From National Fire Prevention Association No. HS-8, 1974.
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</pre>
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<p>
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Clearances from walls. Stovepipes, like stoves, radiate heat. If
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they are installed close to combustible materials, a fire can
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result. The NFPA recommends that a stovepipe be at least 18 inches
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from the nearest combustible material. Closer clearances are allowed
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in some situations (Table 1).
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</p><p>
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Clearances through walls and ceilings. The NFPA does not permit a
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stovepipe to pass through any floor or ceiling or through any fire
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wall or fire partition. However, if a stovepipe must pass through a
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partition other than a fire partition, one of the following
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conditions must be followed:
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</p><p>
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Combustible materials within 18 inches of an uninsulated
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stovepipe must be removed. For a 6-inch diameter pipe, this requires a
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6-inch plus 2 x 18 inch or a 42-inch diameter hole in a combustible
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wall. This hole may be closed or covered with non-combustible
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insulating materials (Figure 3).
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</p><p>
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The 18 inch clearance may be reduced by using a metal thimble or a
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burned fire-clay thimble and surrounding it with at least 8 inches
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of fireproofing material (Figure 3).
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</p>
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<a href="/files/wood-stove-3.gif" target="_blank"><img class="center" src="/files/wood-stove-3.gif"></a>
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<p class="c">
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Figure 3. One method of passing an uninsulated stovepipe through a
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combustible wall. The 18 inch clearance can be reduced to 8 inches by
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extending the thimble (see dotted line) and surrounding it with at
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least 8 inches of fireproofing material.
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</p><p>
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Where a ventilated type metal thimble is used, the
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thimble must be at least 12 inches larger in diameter
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than the stovepipe (Figure 4).
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</p><p>
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Clearance into chimney. If the stovepipe is connected to a masonry
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chimney, it should extend through the near wall of a chimney to the
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inner face of the chimney liner, but not beyond it. A thimble should
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be cemented with high-temperature cement into the masonry wall of the
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chimney and the stovepipe inserted into the thimble without cement
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for easy removal for cleaning and replacement. If a thimble is used,
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the stovepipe must be in tight enough so that a sudden puff in the
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firebox of the stove will not dislodge the pipe.
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</p><p>
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Lengths. The stovepipe should be as straight and short as
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possible. Long, uninsulated stovepipes may increase heating
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efficiency, but they are discouraged because exhaust gases are
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cooled and creosote can develop more rapidly. Creosote accumulations
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create a serious fire hazard. Additional information on creosote
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deposits follows under "Chimney Fires."
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</p><p>
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Sometimes stovepipes may be used in a horizontal position to
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connect a stove to a chimney. In this case, the NFPA code specifies
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that the horizontal run be limited. If an uninsulated stovepipe is
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used, it shall not be longer than 75 percent of the height of the
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chimney above its point of entry into the chimney. If an insulated
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stovepipe is used, - the horizontal run shall not be longer than 100
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percent of the height of the chimney above its point of entry into the
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chim- ney. The chimney is assumed to be a natural draft. The
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horizontal portion of any stovepipe must have an elevated pitch or
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rise of at least y4 inch per linear foot. The point of connection to
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the chimney must be at the higher elevation than the end nearest the
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stove. Each stovepipe joint should be secured with at least three
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sheet metal screws or the equivalent. The joints should fit tightly
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and overlap by about 2 inches with the crimped (male) end pointing
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down into the next piece. This arrangement will prevent creosote
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leaks. When connecting a stove to a chimney, it is preferred to have
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only one 90 degree elbow. Two can be used, however, when necessary.
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</p><p>
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A damper to help control draft is often installed in the stovepipe
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near the stove. Check the stove manufacturer's or dealer's
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recommendation for details. Automatic draft regulators activated by
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a thermostat may be installed according to manufacturer's directions
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and local codes.
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</p>
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<h2>Chimneys
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</h2>
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<p> Chimneys may be masonry or the prefabricated metal type. Masonry
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chimneys are generally installed when the house is being built. In
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some cases, how- ever, they may be added later. Prefabricated metal
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chimneys can be added anytime and are generally used when a masonry
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chimney is not available.
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</p>
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<a href="/files/wood-stove-4.gif" target="_blank"><img class="center" src="/files/wood-stove-4.gif"></a>
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<p class="c">
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Figure 4. A ventilated metal thimble may be
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used to pass a stovepipe through a combustible partition wall.
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</p><p>
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Masonry chimneys. If an existing masonry chimney is to be used,
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check it for leaks. It should also have a flue lining. If the chimney
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is old and deteriorated or does not have a flue lining,
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prefabricated metal chimneys may be inserted into the old flue.
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</p><p>
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When an existing chimney is used, the cross- sectional area of
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the chimney flue should be at least 25 percent greater than that of
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the stovepipe. This will provide adequate draft for exhausting gases
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from the stove. A stovepipe cannot be connected to a fireplace flue
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unless the fireplace opening is sealed off. It is also acceptable if
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the flue is tightly sealed between the fireplace opening and the
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stovepipe entrance to the flue. Fireplace openings and flues should be
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sealed in such a way that future chimney cleaning is. not hampered.
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</p><p>
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Masonry chimneys should also be constructed with proper flashing
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and saddles to prevent roof leaks.
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</p><p>
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Prefabricated Chimneys. Where masonry chimneys are not available,
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prefabricated chimneys may be used. These chimneys come in short
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sections of various lengths that lock together. They may be of double
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wall construction with insulation packed between each wall or of
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triple wall construction designed in such a way that air circulates
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down one wall cavity and up the other. The inner lining of these
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chimneys is usually of corrosion-resistant stainless steel. To be used
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for wood stoves, these chimneys must be listed as UL ALL FUEL
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chimneys. The necessary clearances from combustible materials are
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marked on each section of a UL-listed prefabricated chimney. For the
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insulated double wall-type chimney, the minimum clearance is usually
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two inches. Prefabricated chimneys are efficient and easy to
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install. Creosote build-up is minimized in the insulated type chimney
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because of rapid warming of the inner walls. However, the triple
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wall-type which circulates the air may cause rapid cooling of the
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flue gases and thus increase creosote formation.
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</p>
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<a href="/files/wood-stove-5.gif" target="_blank"><img class="center" src="/files/wood-stove-5.gif"></a>
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<p class="c">
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Figure 5a. A 3-foot minimum chimney height is required where the
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chimney penetrates the roof line less than 10 feet (measured
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horizontally) from the peak.
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</p><p>
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To keep rainwater from entering the house, prefabricated chimneys
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are usually sold with storm collars and flashings as well as caps
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and spark-arresting screens.
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</p><p>
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Chimney height. For a pitched roof, chimney height must be a
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minimum of 3 feet from where it penetrates the roof or at least 2
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feet above the highest roof surface within 10 feet horizontally
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(Figure 5). On flat roofs, the chimneys must be at least 3 feet above
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the roof. These precautions should prevent down drafts as well as roof
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fires from sparks.
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</p><p>
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Multi-flues. The NFPA recommends that room heaters, cook stoves,
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etc. should not be connected to a common flue. Flue gases and sparks
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may pass from one flue opening to another and explode, or the
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poisonous fumes could seep into the house. Multiple connections may
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also result in unsatisfactory draft, and if a chimney fire does occur,
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it cannot be suffocated.
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</p>
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<a href="/files/wood-stove-6.gif" target="_blank"><img class="center" src="/files/wood-stove-6.gif"></a>
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<p class="c">
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Figure 5b. If there are mare than 10 feet between the
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peak and where the chimney penetrates the roof line,
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then at least 2 additional feet of chimney must be added
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above the 10-foot horizontal measurement.
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</p>
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<h2>Chimney Fires
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</h2>
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<p> Chimney fires result when creosote deposits in the stovepipe are
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ignited - usually by a particularly hot fire. Creosote is formed when
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unburned gases (smoke) are cooled and condense inside the stovepipe
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or chimney. When first formed, creosote is a black liquid, and it may
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seep through cracks in masonry chimneys or joint connections in
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stovepipes. It may later dry and form a crust in the stovepipe or
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chimney. With time, these deposits build up and then finally burn,
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resulting in an intense, hot fire which can ignite nearby combustibles
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and the house roof.
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</p><p>
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Creosote deposits cannot be eliminated. It does help, however, to
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use well-seasoned hardwood as fuel and to run a small hot fire rather
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than a large smouldering one. When starting or adding wood to a fire,
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run the fire hot for 10-20 minutes. This will rapidly heat the wood
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and drive off some of the moisture.
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</p><p>
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Frequent chimney inspections are essential. Check for creosote
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deposits after every cord of wood is burned or at least once a
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year. Creosote deposits build up faster in some situations than
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others. For example, the newer "air tight" stoves are very efficient
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and tend to form creosote deposits faster. Sooner or later, a
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thorough chimney cleaning will be necessary.
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</p>
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<a href="/files/wood-stove-7.gif" target="_blank"><img class="center" src="/files/wood-stove-7.gif"></a>
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<p class="c">
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Figure 6. Creosote and soot deposits loosened from chimney with wire
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brush. These deposits accumulated in less than two months.
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</p>
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<p>
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To clean prefabricated chimneys, many stove dealers sell round wire
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brushes which can be attached to small diameter metal pipes or
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ropes. The pipe or rope with the brush attached is then moved up and
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down in the chimney until all creosote deposits are removed. The
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deposits should fall to the bottom of the chimney and must be
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removed (Figure 6). Although not as effective, burlap bags filled
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with straw and weights such as rocks can be pulled up and down the
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chimney to remove creosote deposits.
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</p><p>
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If a chimney fire does occur, limit the air supply to the
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fire. Discharge a fire extinguisher into the stove and call the fire
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department. A multi-purpose dry chemical (Class ABC) fire extinguisher
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is preferred. This type is appropriate for other home fires as well.
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</p>
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<h2>Summary
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</h2>
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<p> Wood stoves can be an economical source of home heat. However, if
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they are not properly installed, maintained and operated, serious
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house fires and even death can result. This bulletin outlines
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installation procedures as recommended by the National Fire
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Prevention Association. These recommendations are written to apply to
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all situations and, therefore, are general in nature. When installing
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your stove, consult with local officials for details and follow the
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manufacturer's recommendations. Always operate your stove in a
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sensible fashion, and periodically inspect it for damage. Routinely
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clean creosote deposits from the chimney. Keep a fire extinguisher
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present at all times, and guard against complacency.
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</p>
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<h2>Suggested Readings
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</h2>
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<p>
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Chimneys, Fireplaces, and Vents. 1977. National Fire Prevention
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Association, 470 Atlantic Ave., Boston, MA 02210, 50 pp. ($3.00)
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</p><p>
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Heat-Producing Appliance Clearances, 1976. National Fire Prevention
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Association, 470 Atlantic Ave., Boston, MA 02210, 14 pp. ($3.00)
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</p><p>
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Using Wood and Coal Stoves Safely, 1974. National Fire Prevention
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Association, 470 Atlantic Ave., Boston, MA 02210, 12 pp. ($2.00)
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</p><p>
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The Woodburner's Encyclopedia, 1977. Vermont Crossroads Press, Box
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333, Waitsfield, VT 05673, 162 pp. ($7.95)
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</p><p>
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Fireplaces and Chimneys. U.S. Department of Agriculture,
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Agricultural Research Service, Farmers' Bulletin No. 1889, Reprinted
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September 1977.
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</p>
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<hr>
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<p class="C">Library of GigaChad | <a href="/" target="_blank">GigaChad</a></p>
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