10
Fu rnace
W ater
Heater
Outlet Air
Chimney or Gas Vent
N OTE: The inlet and outlet a ir
openings m ust each have a free
area of not less than one square
inch per 4000 B TU of the
total input rating of all equipm ent
in the e nclosure.
Inlet a ir duct
[end s 1 ft (3 00 mm )
abo ve floor]
Ventilation lou vers
(ea ch end of attic)
Equipment Located in Confined Spaces; All Air from Outdoors
Through Ventilated Attic. See 5.3.3-b.
3. When communicating with the outdoors through
horizontal ducts, each opening shall have a minimum
free area of 1 square inch per 2,000 BTU per hour of
total input rating of all equipment in the enclosure.
Furnace
Water
Heater
Chimney or Gas Vent
NOTE: The air duct openings
must have a free area of not
less than one square inch per
2000 BTU of the total input
rating of all equipment in the
enclosure*.
Outlet air duct
Inlet air duct
Equipment Located in Confined Spaces;
All Air from Outdoors. See 5.3.3-b.
*If the appliance room is located against an outside wall and the
air openings communicate directly with the outdoors, each opening
shall have a free area of not less than one square inch per 4,000
BTU per hour of the total input rating of all appliances 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 not be less than 3 inches.
Furnace
Water
Heater
Opening
Chimney or Gas Vent
NOTE: The single opening must have
a free area of not less than one
square inch per 3000 BTU of
the total input rating of all equip-
ment in the enclosure, but not less than
the sum of the areas of all vent
connectors in the confined space.
Alternate
Opening
Location
Equipment Located in Confined Spaces; All Air from Outdoors -
Single Air Opening. See 5.3.3-b.
5. One permanent opening may be permitted, provided
the equipment has clearances of at least 1” from the
sides and back and 6” from the front. The opening shall
communicate directly with the outdoors and must be
located within 12” of the top of the enclosure. The
minimum free area of the opening shall be 1 square
inch per 3,000 BTU per hour of total input rating of all
equipment in the enclosure. The minimum free area
shall not be less than the sum of the areas of all vent
connectors in the confined space.
5.3.4 Specially Engineered Installations:
The requirements of 5.3.3 shall not necessarily govern when
special engineering, approved by the authority having
jurisdiction, provides an adequate supply of air for combustion,
ventilation, and dilution of flue gases.
5.3.5 Louvers and Grilles:
In calculating free area in 5.3.3, consideration shall be given
to the blocking effect of louvers, grilles or screens protecting
openings. Screens used shall not be smaller than 1/4 inch
mesh. If the area through a design of louver or grille is known,
it should be used in calculating the size of opening required
to provide the free area specified. If the design and free area
is not known, it may be assumed that wood louvers will have
20-25 percent free area and metal louvers and grilles will
have 60-75 percent free area. Louvers and grilles shall be
fixed in the open position or interlocked with the equipment
so that they are opened automatically during equipment
operation.
5.3.6 Special Conditions Created by Mechanical Exhausting or
Fireplaces:
Operation of exhaust fans, ventilation systems, clothes dryers,
or fireplaces may create conditions requiring special attention
to avoid unsatisfactory operation of installed gas utilization
equipment.
