6
(6) inches (15.2 cm) of the top and one commencing
within six (6) inches (15.2 cm) from 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.
A) When communicating directly with the outdoors,
each opening shall have a minimum free area of
one (1) square inch per 4,000 BTUH (5.5 cm
2
/kW)
of the total input rating of all gas appliances in the
enclosure (see Figure 5).
B) When communicating with the outdoors through
vertical ducts, each opening shall have a minimum
free area of one (1) square inch per 4,000 BTUH (5.5
cm
2
/kW) of the total input rating of all gas appliances
in the enclosure (see Figure 6).
C) When communicating with the outdoors through
horizontal ducts, each opening shall have a mini-
mum free area of one (1) square inch per 2,000
BTUH (11.0 cm
2
/kW) of the total input rating of
all gas appliances in the enclosure (see Figure 7).
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 dimen-
sion of rectangular air ducts shall not be less than
three (3) inches (7.62 cm).
Louvers and Grilles
In calculating free area for ventilation and com-
bustion air supply openings, consideration must be
given to the blocking effect of louvers, grilles or
screens protecting the openings. Screens must not
be smaller than
1
/4 inch (6.4 mm) mesh. If the free
area through a particular design of louver or grille
is known, it should be used in calculating the size
of opening required to provide the free area speci-
fied. If the design and free area is not known, it may
be assumed that wood louvers and grilles will allow
20-25% free area and metal louvers and grilles will
allow 60-75% free area. Louvers and grilles must
be installed in the open position or interconnect-
ed with the water heater so that they are opened
automatically during water heater operation.
Corrosive Atmospheres
If this water heater is to be installed in a beauty
shop, barber shop, photo processing lab, dry cleaning
establishment, a building with an indoor pool or
near a chemical storage area, it is imperative that
the combustion and ventilation air be drawn from out-
side these areas. These particular environments
contain products such as aerosol sprays, detergents,
bleaches, cleaning solvents, refrige rants and other
volatile compounds that, in addition to being highly flam-
mable, become highly corrosive acid compounds when
burned. Exposure to such compounds can be hazard-
ous and lead to premature product failure.
INSTALLATION INSTRUCTIONS
Figure 7
Figure 6
Figure 5
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