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COMBUSTION AND VENTILATION AIR
When installed, this gas appliance must be provided with fresh air for combustion,
ventilation, and dilution of hot flue gases. The minimum required volume of the
area where the appliance is installed must be 50 cubic feet per 1,000 btu/hr.
If installed in an area of the home that is considered an unconfined space, the
natural infiltration of air around windows and doors will be adequate. If the area
is considered a confined space (less than 50 cubic feet per thousand btu), fresh
air can be supplied by providing two permanent openings into adjoining rooms.
Each opening shall have a minimum free area of one square inch per 1,000 btu
per hour of the total input rating of all gas appliances in the confined space, but
not less than 100 square inches. One of the openings shall be within 12 inches
of the ceiling and one within 12 inches of the floor. See Figure E-1 (to the right).
If the home is of unusually tight construction (new and remodeled homes), free air
must be supplied through opening(s) to the outdoors. This can be accomplished
by providing 2 permanent openings, one commencing within 12 inches of the
ceiling and one within 12 inches of the floor. These openings shall communicate
directly with the outdoors, or spaces that communicate freely with the outdoors,
such as a ventilated attic and crawl space through galvanized or equivalent
corrosion-resistant ducts. Exception: Unobstructed stud and joist spaces are
acceptable ducts provided that not more than one fire block is removed. Special
provisions must be taken to insure that these stud and joist spaces cannot be
blocked with insulation or other objects. Each of these openings using vertical
ducts shall have a minimum free area of one square inch per 4,000 btu/hr of
total input rating of all gas appliances. See Figures E-2 (to the right) and E-3
(below). If horizontal ducts are used, the minimum free area shall be one square
inch per 2,000 btu/hr of total input rating of all gas appliances.
Fresh make-up air can also be provided through a duct to one permanent
opening commencing within 12 inches of the ceiling. The minimum free area of
this opening shall be one square inch per 3,000 btu/hr of the total input rating of
all gas appliances but not less than the sum of the areas of all vent connectors
in the space. See Figure E-4 (below).
When calculating the amount of fresh air needed you must include make-up
air requirements for the operation of exhaust fans, kitchen ventilation systems,
clothes dryers, and fireplaces.
Additional information can be found in the latest edition of ANSI Z223.1
(National Fuel Gas Code).
Fig. E-3
ALL
COMBUSTION
AIR FROM
OUTDOORS
THROUGH
VENTILATED
ATTIC
1017480-A
UL Listed Vent Cap
UL Listed Gas Vent
Ventilation Louvers
(Each End of Attic)
Inlet
Outlet Air
Grille
Inlet Air Duct
Inlet
(Ends
Grille
1 ft.
[300mm]
Above
Floor)
Fig. E-4
ALL
COMBUSTION
AIR FROM
OUTDOORS
THROUGH
SINGLE
COMBUSTION
AIR OPENING
Page 6
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ALL COMBUSTION AIR FROM
ADJACENT INDOOR SPACES
THROUGH INDOOR COMBUSTION
AIR OPENINGS
UL Listed Vent Cap
UL Listed Gas Vent
Opening
Opening
ALL COMBUSTION AIR FROM
OUTDOORS. INLET AIR FROM
VENTILATED CRAWL SPACE &
OUTLET AIR TO VENTILATED ATTIC
UL Listed Vent Cap
UL Listed Gas Vent
Ventilation
Louvers
Outlet Air
Inlet Air
Ventilation
Louvers for Unheated Crawl Space
UL Listed Vent Cap
UL Listed Gas Vent
Opening
Alternate
Opening
Location
Fig. E-1
Fig. E-2
(Each
End of
Attic)
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