Intertek MVM97 Series Installation Instructions Manual page 13

9.3.4 Combination Indoor and Outdoor Combustion Air. The use of a combination of indoor and outdoor combustion air shall be in accordance with
(1) through (3) (see example calculation in Annex J]:
(1) Indoor Openings: Where used, openings connecting the interior spaces shall comply with 9.3.2.3.
(2) Outdoor Opening(s) Location. Outdoor opening(s) shall be located in accordance with 9.3.3.
(3) Outdoor Opening(s) Size. The outdoor opening(s) size shall be calculated in accordance with the following:
(a) The ratio of the interior spaces shall be the available volume of all communicating spaces divided by the required volume.
(b) The outdoor size reduction factor shall be 1 minus the ratio of interior spaces.
(c) The minimum size of outdoor opening(s) shall be the full size of outdoor opening(s) calculated in accordance with 9.3.3, multiplied by the
reduction factor. The minimum dimension of air openings shall not be less than 3 in. (80 mm).
9.3.5 Engineered Installations. Engineered combustion air installations shall provide an adequate supply of combustion, ventilation, and dilution air and
shall be approved by the authority having jurisdiction.
9.3.6 Mechanical Combustion Air Supply. Where all combustion air is provided by a mechanical air supply system, the combustion air shall be
supplied form outdoors at the minimum rate of 0.35 ft
9.3.6.1 Where exhaust fans are installed, additional air shall be provided to replace the exhausted air.
9.3.6.2 Each of the appliances served shall be interlocked to the mechanical air supply system to prevent main burner operation where the mechanical air
supply system is not in operation.
9.3.6.3 Where combustion air is provided by the building's mechanical ventilation system, the system shall provide the specified combustion air rate in
addition to the required ventilation air.
9.3.7 Louvers, Grilles, and Screens.
9.3.7.1 Louvers and Grilles. The required size of openings for combustion, ventilation, and dilution air shall be based on the net free area of each opening.
Where the free area through a design of louver or grille or screen is known, it shall be used in calculating the size opening required to provide the free area
specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers will have 25 percent free area, and metal
louvers and grilles will have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position.
9.3.7.2 Minimum Scree Mesh Size. Screens shall not be smaller than 1/4 in. mesh.
9.3.7.3 Motorized Louvers. Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner
ignition and during main burner operation. Means shall be provided to prevent the main burner form igniting should the louver fail to open during burner
startup and to shut down the main burner if the louvers close during burner operation.
9.3.8 Combustion Air Ducts. Combustion air ducts shall comply with 9.3.8.1 through 9.3.8.8.
9.3.8.1 Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.
Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than
one fireblock is removed.
9.3.8.2 Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances.
9.3.8.3 Ducts shall serve a single space.
9.3.8.4 Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts servicing
upper and lower combustion air openings shall be maintained to the source of combustion air.
9.3.8.5 Ducts shall not be screened where terminating in an attic space.
9.3.8.6 Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air.
9.3.8.7 The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry, metal, or factory built
chimney shall not be used to supply combustion air.
Exception: Direct vent appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacture's
installation instructions.
9.3.8.8 Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at
least 12 in. (300 mm) vertically from the adjoining grade level.
3 /min per 1000 Btu/hr (0.034 m 3 /min per kW) for all appliances located within the space.
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