Advertisement
Figure A.9.3.3.2 All Combustion Air
From Outdoors through Single Combustion Air Opening.
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 calcu-
lated 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
(0.034 m
3
/min per kW) for all appliances located within the space.
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 mechani-
cal air supply system to prevent main burner operation where the mechani-
cal air supply system is not in operation.
9.3.6.3 Where combustion air is provided by the building's mechanical ven-
tilation 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 combus-
tion, 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 Screen 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 pre-
vent 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 move-
ment 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 servic-
ing 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
3
/min per 1000 Btu/hr
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.
13
Advertisement
