PRODUCT DESIGN
23
(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, mul-
tiplied 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 installa-
tions 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
3
/min per 1000 Btu/
hr (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 me-
chanical 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 com-
bustion, 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 lou-
vers 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 hav-
ing 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 open-
ings 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, spe-
cial 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.
Category I Venting (Vertical Venting)
(80% Furnaces Only)
WARNING
T
O PREVENT POSSIBLE PERSONAL INJURY OR DEATH DUE TO
ASPHYXIATION, NON-CONDENSING GAS FIRED WARM AIR FURNACES MUST
BE
C
ATEGORY
I
VENTED.
D
O NOT VENT ANY OF THESE FURNACES USING
C
ATEGORY
III
VENTING.
Category I Venting is venting at a non-positive pressure. A
furnace vented as Category I is considered a fan-assisted
appliance and does not have to be "gas tight."
NOTE:
Single-
Stage and Two-Stage gas furnaces with induced draft blow-
ers draw products of combustion through a heat exchanger
allowing in some instances common venting with natural
draft appliances (i.e. water heaters).
All installations must be vented in accordance with National
Fuel Gas Code NFPA 54/ANSI Z223.1 - latest edition. In
Canada, the furnaces must be vented in accordance with
the National Standard of Canada, CAN/CGA B149.1 and
CAN/CGA B149.2 - latest editions and amendments.
NOTE:
The vertical height of the Category I venting system
must be at least as great as the horizontal length of the
venting system.
WARNING
T
O PREVENT POSSIBLE DEATH OR PERSONAL INJURY DUE TO
ASPHYXIATION, COMMON VENTING WITH OTHER MANUFACTURER'S
INDUCED DRAFT APPLIANCES IS NOT ALLOWED.
