1018454-D
Page 6
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 1,000 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 1-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 1-B and 1-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 1-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).
COMBUSTION AND VENTILATION AIR
FIG. 1-C
UL Listed Vent Cap
UL Listed Gas Vent
Ventilation Louvers
(each end of attic)
Outlet Air
Inlet Air Duct
Inlet
Grille
Inlet
Grille
Ends
1 ft.,
300mm
above
floor.
All Combustion Air from Outdoors
Through Ventilated Attic
FIG. 1-D
UL Listed Vent Cap
UL Listed Gas Vent
Opening
Alternate
Opening
Location
All Combustion Air From Outdoors
Through Single Combustion Air Opening
FIG. 1-A
UL Listed Vent Cap
UL Listed Gas Vent
Opening
Opening
All Combustion Air from Adjacent Indoor Spaces
Through Indoor Combustion Air Openings
FIG. 1-B
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. Inlet Air from
Ventilated Crawl Space & Outlet Air to Ventilated Attic
