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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 should 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 A.
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
Figure B and C. 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 D.
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).
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 AND
OUTLET AIR TO VENTILATED ATTIC
UL Listed Vent Cap
UL Listed Gas Vent
Ventilation Louvers
(each end of attic)
Outlet Air
Inlet Air
Ventilation
louvers for unheated
crawl space
ALL COMBUSTION AIR FROM OUTDOORS
THROUGH VENTILATED ATTIC
ALL COMBUSTION AIR FROM OUTDOORS
THROUGH SINGLE COMBUSTION AIR OPENING
UL Listed Vent Cap
UL Listed Gas Vent
Ventilation Louvers
(each end of attic)
Outlet Air
Inlet Air Duct (Ends 1 Ft.
[300 mm] above floor)
UL Listed Vent Cap
UL Listed Gas Vent
Opening
Alternate
opening
location
FIGURE A
FIGURE C
FIGURE B
FIGURE D
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