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GENERAL VENTING REQUIREMENTS AND
NON-DIRECT VENT (cont.)
B. USING OUTDOOR AIR FOR COMBUSTION:
IMPORTANT: Do not take air from an attic space that is
equipped with power ventilation.
The confined space must communicate with the outdoors in
accordance with Methods 1 or 2 below. The minimum dimen-
sion of air openings shall not be less than 3 inches. Where
ducts are used, they shall be of the same cross-sectional
area as the free area of the openings to which they connect.
METHOD 1:
Two permanent openings, one located within 12 inches of the
top and one located within 12 inches of the bottom of the en-
closure, shall be provided. The openings shall communicate
#%
$
TABLE 9: MINIMUM FREE AREA REQUIRED
$
FOR EACH OPENING (WHEN TWO OPENINGS
' ) $
%
ARE USED) WITH A FURNACE:
$
1. LOCATED IN A CONFINED SPACE
$
2. USING OUTDOOR AIR FOR COMBUSTION
3. COMMUNICATING DIRECTLY TO THE
3.
OUTSIDE THROUGH AN OPENING OR
3.
THROUGH A VERTICAL DUCT.
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TABLE 10: MINIMUM FREE AREA REQUIRED
$
FOR EACH OPENING (WHEN TWO OPENINGS
' ) $
%
ARE USED) WITH A FURNACE:
$
1. LOCATED IN A CONFINED SPACE
$
2. USING OUTDOOR AIR FOR COMBUSTION
3. COMMUNICATING DIRECTLY TO THE
3.
OUTSIDE THROUGH A HORIZONTAL DUCT.
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directly, or by ducts, with the outdoors or spaces (crawl or
attic) that freely communicate with the outdoors.
A. Where directly communicating with the outdoors through
an opening or where communicating to the outdoors through
vertical ducts as shown in Figure 14, each opening shall
have a minimum free area of 1 square inch for each 4,000
BTUH of total appliance input rating of all equipment in the
enclosure. Table 9 below specifies the minimum area for
each of the 2 combustion air openings and minimum round
duct diameter for direct openings and vertical ducting only.
B. Where communicating with the outdoors through horizon-
tal ducts, each opening shall have a minimum free area of 1
square inch for each 2,000 BTUH of total appliance input rat-
ing of all equipment in the enclosure (see Figure 15). Table
10 specifies the minimum area for each of the 2 combustion
TABLE 11: MINIMUM FREE AREA REQUIRED
$
FOR AN OPENING (WHEN ONE OPENING IS
' ) $
%
USED) WITH A FURNACE:
1. LOCATED IN A CONFINED SPACE
2. USING OUTDOOR AIR FOR COMBUSTION
3. COMMUNICATING DIRECTLY TO THE
3.
OUTSIDE.
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FIGURE 13
NON-DIRECT VENT
AIR FROM
HEATED
SPACE
GUIDELINES
%
$
&)
$
$
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ST-A1194-19
FIG C
53
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