Operating instructions

C. Hazardous Locations
II. AIR FOR COMBUSTION AND VENTILATION
Provisions for adequate combustion and ventilation air must be
provided in accordance with Section 5.3, Air for Combustion and
Ventilation, of the NFGC or applicable provisions of local building
codes.
Canadian installations must be in accordance with NSCNGPIC
and all authorities having jurisdiction.
CAUTION: Air for combustion must not be contami-
nated by halogen compounds which include fluoride,
chloride, bromide, and iodide. These elements are found
in aerosol sprays, detergents, bleaches, cleaning solvents,
salts, air fresheners, and other household products.
CAUTION: The operation of exhaust fans, kitchen ven-
tilation fans, clothes dryers, or fireplaces could create a
negative air pressure condition at the furnace. Make-up
air must be provided for these devices, in addition to that
required by the furnace.
All fuel-burning equipment must be supplied with air for combus-
tion of the fuel. Sufficient air MUST be provided to ensure there
will not be a negative pressure in equipment room or space. In
addition, a positive seal MUST be made between furnace cabinet
and return-air duct to avoid pulling air from the burner area and
draft safeguard opening into circulating air.
The requirements for combustion and ventilation air depend upon
whether furnace is located in a CONFINED or UNCONFINED
space.
A. Unconfined Space
An unconfined space must have at least 50 cu ft for each 1000
Btuh of input for all appliances (such as furnaces, clothes dryer,
water heaters, etc.) in the space.
For Example:
331AAV FURNACE
HIGH-FIRE INPUT
BTUH
MINIMUM SQ FT
WITH
7-1/2 FT CEILING
63,000 420
84,000 560
105,000 700
123,000 820
If the unconfined space is constructed unusually tight, air for
combustion and ventilation MUST come from either the outdoors
or spaces freely communicating with outdoors. Combustion and
ventilation openings must be sized the same as for a confined
space as defined below. Return air must not be taken from the
room unless equal or greater amount of air is supplied to the room.
B. Confined Space
A confined space is defined as a space whose volume is less than
50 cu ft per 1000 Btuh of total input ratings of all appliances
installed in that space. A confined space MUST have provisions
for supplying air for combustion, ventilation, and dilution of flue
gases using 1 of the following methods.
NOTE: In determining free area of an opening, the blocking
effect of louvers, grilles, and screens must be considered. If free
area of louver or grille design is unknown, assume that wood
louvers have a 20 percent free area and metal louvers or grilles
have a 60 percent free area. Screens, when used, must not be
smaller than 1/4-in. mesh. Louvers and grilles must be constructed
so they cannot be closed.
The size of the openings depends upon whether air comes from
outside of the structure or an unconfined space inside the structure.
1. All air an unconfined space from inside the structure
requires 2 openings (for structures not usually tight):
a. Each opening MUST have at least 1 sq in. of free area
per 1000 Btuh of total input for all equipment within the
confined space, but not less than 100 sq in. per opening.
(See Fig. 3 and Table 2.) The minimum dimension of air
openings shall not be less than 3 in.
b. If the building is constructed unusually tight, a perma-
nent opening directly communicating with the outdoors
shall be provided. (See item 2 below.)
c. If furnace is installed to obtain return air directly from
hallway or space adjacent to furnace, all air for combus-
tion must come from outdoors.
2. Air from outside the structure requires 1 of the following
methods:
a. If combustion air is taken from outdoors through 2
vertical ducts, the openings and ducts MUST have at
least 1 sq in. of free area per 4000 Btuh of total input for
all equipment within the confined space. (See Fig. 4 and
Table 2.)
b. If combustion air is taken from outdoors through 2
horizontal ducts, the openings and ducts MUST have at
least 1 sq in. of free area per 2000 Btuh of total input for
all equipment within the confined space. (See Fig. 4 and
Table 2.)
c. If combustion air is taken from outdoors through a single
opening or duct (horizontal or vertical) commencing
within 12 in. of the top of the confined space, opening
and duct MUST have at least 1 sq in. of free area per
3000 Btuh of the total input for all equipment within the
confined space and not less than the sum of the areas of
all vent connectors in the confined space. (See Fig. 4 and
Table 2.) Equipment clearances to the structure shall be
at least 1 in. from the sides and back and 6 in. from the
front of the appliances.
WARNING: When furnace is installed in a residential
garage, it must be installed so that burners and ignition
sources are located a minimum of 18 in. above floor. The
furnace must be located or protected to avoid physical
damage by vehicles. When furnace is installed in a public
garage, airplane hangar, or other building having a
hazardous atmosphere, unit must be installed in accor-
dance with requirements of National Fire Protection
Association, Inc.
A93044
18-IN. MINIMUM
TO BURNERS
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