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Provision for combustion and ventilation air must be in accordance with Section 5.3, Air for Combustionand
Ventilation, of the National Fuel Gas Code, ANSI Z223.1-1atest revision, or applicable provisionsof the local building codes.
WARNING
Besure to provideenough freshairfor combustion.
Enoughair insurespropercombustionand assuresthat
nohazardwilldevelopdueto the lackofoxygen.
You must provide for enough fresh air to assure proper
combustion. The fire in the boiler uses oxygen. It must have
a continuous supply. The air in a house contains only enough
oxygen to supply the burner for a short time. Outside air
must enter the house to replace that used by the burner.
Study following examples 1 and 2 to determine your fresh
air requirements,
EXAMPLE 1: Boiler Located in Unconfined Space
If your boiler is in an open area (unpartitioned basement)
in a conventional house, the air that leaks through the cracks
around doors and windows will usually be adequate to provide
air for combustion. The doors should not fit tightly. Do not
caulk the cracks around the windows,
An unconfined space is defined as a space whose volume
is not less than 50 cubic feet per 1,000 Btu per hour of
the total input rating of all appliances installed in that space.
EXAMPLE 2: Boiler Located in Confined Space
A. All Air from Inside the Building: The confined space
shall be provided with two permanent openings
communicating directly with an additional room(s) of
sufficient volume sothat thecombined volume of all spaces
meets the criteria for an unconfined space. The total input
of all gas utilization equipment installed in the combined
space shall be considered in making this determination.
Each opening shall have a minimum free area of one
square inch per 1,000 Btu per hour of thetotal input rating
of all gas utilization equipment in the confined space, but
not less than 100 square inches. One opening shall be
within 12 inches of the top and one within 12 inches of
the bottom of the enclosure,
B, All Air from Outdoors: The confined space shall be
provided with two permanent openings, one commencing
within 12 inches of the top and one commencing within
12 inches of the bottom of the enclosure. The openings
shall communicate directly, or by ducts, with the outdoors
or spaces (crawl or attic) that freely communicate with
the outdoors.
1. When directly communicating with the outdoors, each
opening shall have a minimum free area of one square
inch per 4,000 Btu per hour of total input rating of alt
equipment in the enclosure.
NOTE
If you use a fireplace or a kitchen or bathroom exhaust
fan, you should install an outside air intake. These devices
will rob the boiler and water heater of combustion air.
2. When communicating with the outdoorsthrough vertical
ducts, each opening shall have a minimum free area
of one square inch per 4,000 Btu per hour of total
input rating of all equipment in the enclosure.
3. When communicating with the outdoors through
horizontal ducts, each opening shall have a minimum
free area of one square inch per 2,000 Btu per hour
of total input rating of all equipment in the enclosure.
4. When ducts are used, they shall be of the same cross-
sectional area as the free area of the openings to which
they connect. The minimum dimension of rectangular
air ducts shall be not less than three inches.
Fresh Air Duct Capacities for Ducts Supplying Fresh Air to
boiler in tightly constructed houses. British Thermal Units per
hour Input (Btuh)*.
Fresh Air 1/,-Mesh Wood Metal
Duct Screen Louvers Louvers
Size Btuh Btuh Btuh
3' x 12' 144,000 36,000 108,000
8" x 8' 256,000 64,000 192,000
8' x 12" 384,000 96,000 288,000
8V2' x 16' 512,000 128,000 384,000
*Basedon opening covered by V4"meshscreen,woodIouvers,ormetallouvers.
FRESH AIR DUCT
FOR TIGHTLY
SEALED HOUSE
FRESH
AIR
DUCT
,_,* 6
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