A.O. Smith VB/VW- 1000 - Manual (Page 12)

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for the openings that provide fresh air into confined spaces
only. Do not refer to these illustrations for the purpose of vent
installation. See Venting Installation on page 18 for complete
venting installation instructions.
OUTDOOR AIR THROUGH TWO OPENINGS
FIGURE 9A.
The confined space should be provided with two permanent
openings, one commencing within 12 inches (300 mm) of the
top and one commencing within 12 inches (300 mm) of the
bottom of the enclosure. The openings should communicate
directly with the outdoors. See Figure 9A.
Each opening should have a minimum free area of 1 square
inch per 4,000 Btu/hr (550 mm 2 per kW) of the aggregate
input rating of all appliances installed in the enclosure. Each
opening should not be less than 100 square inches (645 cm2).
OUTDOOR AIR THROUGH ONE OPENING
FIGURE 9B.
Alternatively a single permanent opening, commencing within 12
inches (300 mm) of top of enclosure, should be provided. See
Figure 9B. The appliance should have clearances of at least 1
inch (25 mm) from sides and back and 6 inches (150 mm) from
front. The opening should directly communicate with outdoors
or should communicate through a vertical or horizontal duct to
outdoors or spaces that freely communicate with outdoors and
should have a minimum free area of the following:
1. 1 square inch per 3000 Btu/hr (700 mm
2 per kW) of the total
input rating of all appliances located in the enclosure, and
2. Not less than the sum of areas of all vent connectors in
the space.
OUTDOOR AIR THROUGH TWO HORIzONTAL DUCTS
FIGURE 9C.
The confined space should be provided with two permanent
horizontal ducts, one commencing within 12 inches (300 mm)
of the top and one commencing within 12 inches (300 mm)
of the bottom of the enclosure. The horizontal ducts should
communicate directly with the outdoors. See Figure 9C.
Each duct opening should have a minimum free area of 1 square
inch per 2,000 Btu/hr (1100 mm 2 per kW) of the aggregate input
rating of all appliances installed in the enclosure.
When ducts are used, they should 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 should be not less
than 3 inches.
OUTDOOR AIR THROUGH TWO VERTICAL DUCTS
The illustrations shown in this section of the manual are a reference
for the openings that provide fresh air into confined spaces only.
Do not refer to these illustrations for the purpose of vent installation.
See Venting Installation on page 19 for complete venting installation
instructions.
FIGURE 9D.
The confined space should be provided with two permanent
vertical ducts, one commencing within 12 inches (300 mm) of
the top and one commencing within 12 inches (300 mm) of the
bottom of the enclosure. The vertical ducts should communicate
directly with the outdoors. See Figure 9D.
Each duct opening should have a minimum free area of 1 square
inch per 4,000 Btu/hr (550 mm 2 per kW) of the aggregate input
rating of all appliances installed in the enclosure.
When ducts are used, they should be of same cross sectional area
as free area of openings to which they connect. The minimum
dimension of rectangular air ducts should be not less than 3 inches.