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19
Figure 19
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 short side
dimension of rectangular air ducts shall not be less
than 3” (76mm) (see Figure 20).
Figure 20
5. Alternatively a single permanent opening may
be used when communicating directly with the
outdoors, or with spaces that freely communicate
with the outdoors. The opening shall have a
minimum free area of 1 square inch per 3,000 Btu/hr
(8.3 cm
2
/kW) of total input rating of all equipment in
enclosure (see Figure 21).
Figure 21
6. Louvers and Grilles: In calculating free area,
consideration shall be given to the blocking effect
of louvers, grilles or screens protecting openings.
Screens used shall not be smaller than 1/4” (6.4mm)
mesh. If the free area through a design of louver
or grille is known, it should be used in calculating
the size opening required to provide the free area
speci
fi
ed. If the design and free area is not known,
it may be assumed that wood louvers will be 20-25
percent free area and metal louvers and grilles will
have 60-75 percent free area. Louvers and grilles
shall be
fi
xed in the open position or interlocked with
the equipment so that they are opened automatically
during equipment operation.
7. Special Conditions Created by Mechanical
Exhausting or Fireplaces: operation of exhaust fans,
ventilation systems, clothes dryers or
fi
replaces may
create conditions requiring special attention to avoid
unsatisfactory operation of installed gas utilization
equipment.
CHEMICAL VAPOR CORROSION
CORROSION OF THE FLUEWAYS AND VENT SYSTEM
MAY OCCUR IF AIR FOR COMBUSTION CONTAINS
CERTAIN CHEMICAL VAPORS. SUCH CORROSION MAY
RESULT IN FAILURE AND RISK OF ASPHYXIATION.
Spray can propellants, cleaning solvents, refrigerator and
air conditioning refrigerants, swimming pool chemicals,
calcium and sodium chloride (water softener salt), waxes,
and process chemicals are typical compounds which
are potentially corrosive. Do not store products of this
sort near the heater. Also air which is brought in contact
with the heater should not contain any of the chemicals.
If necessary, uncontaminated air should be obtained
from remote or outside sources. The Limited Warranty is
voided when failure of water heater is due to a corrosive
atmosphere. See “Limited Warranty” for complete terms
and conditions.
