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COMBUSTION AND VENTILATION AIR (cont.)
COMBUSTION AIR REQUIREMENTS: CONFINED AND
UNCONFINED SPACES
TABLE 9 : MINIMUM FREE AREA REQUIRED
T BLE 3: MINIMUM FREE RE REQUIRED
FOR EACH OPENING (WHEN TWO OPENINGS
FOR E CH OPENING (WHEN TWO OPENINGS
ARE USED) WITH A FURNACE:
RE USED) WITH
1. LOCATED IN A CONFINED SPACE
1. LOC TED IN
CONFINED SP CE
2. USING OUTDOOR AIR FOR COMBUSTION
2. USING OUTDOOR IR FOR COMBUSTION
3. COMMUNIC TING DIRECTLY TO THE
3. COMMUNICATING DIRECTLY TO THE
3.
OUTSIDE THROUGH N OPENING OR
OUTSIDE THROUGH AN OPENING OR
3.
THROUGH
VERTIC L DUCT.
THROUGH A VERTICAL VENT DUCT.*
Free Area for
Total Input for
Each Opening
ALL Gas
when 2 Separate
Appliances
Openings are
(BTUH)
used (sq inches)
50,000
75,000
100,000
125,000
150,000
A. Where directly communicating with the outdoors through an
vertical ducts as shown in Figure 11, each opening shall
opening or where communicating to the outdoors through
have a minimum free area of 1 square inch for each 4,000
enclosure. Table 3 specifies the minimum area for
BTUH of total appliance input rating of all equipment in the
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
ing of all equipment in the enclosure (see Figure 12). Table 4
square inch for each 2,000 BTUH of total appliance input rat-
TABLE 1 0: MINIMUM FREE AREA REQUIRED
T BLE 4: MINIMUM FREE RE REQUIRED
FOR EACH OPENING (WHEN TWO OPENINGS
FOR E CH OPENING (WHEN TWO OPENINGS
ARE USED) WITH A FURNACE:
RE USED) WITH
FURN CE:
1. LOC TED IN
CONFINED SP CE
1. LOCATED IN A CONFINED SPACE
2. USING OUTDOOR IR FOR COMBUSTION
2. USING OUTDOOR AIR FOR COMBUSTION
3. COMMUNIC TING DIRECTLY TO THE
3. COMMUNICATING DIRECTLY TO THE
3.
OUTSIDE THROUGH
OUTSIDE THROUGH A H ORIZONTAL DUCT.
Free Area for
Total Input for
Each Opening
ALL Gas
when 2 Separate
Appliances
Openings are
(BTUH)
used (sq inches)
50,000
75,000
100,000
125,000
150,000
16
FURN CE:
Round Pipe Duct
Diameter ( Ver cal
Duct Only) (inches)
13
5
19
5
25
6
32
8
38
8
HORIZONT L DUCT.
Round Pipe Duct
Diameter
(Horizontal Duct
Only) (inches)
25
6
38
8
50
8
63
10
75
10
T BLE 5: MINIMUM FREE RE REQUIRED
TABLE 1 1: MINIMUM FREE AREA REQUIRED
FOR E CH OPENING (WHEN TWO OPENINGS
FOR AN OPENING (WHEN O N E OPENING IS
USED) WITH A FURNACE:
RE USED) WITH
FURN CE:
1. LOC TED IN
CONFINED SP CE
1. LOCATED IN A CONFINED SPACE
2. USING OUTDOOR IR FOR COMBUSTION
2. USING OUTDOOR AIR FOR COMBUSTION
3. COMMUNIC TING DIRECTLY TO THE
3. COMMUNICATING DIRECTLY TO THE
3.
OUTSIDE THROUGH
OUTSIDE.
*
Total Input for
Free Area for an
ALL Gas
Opening when 1
Appliances
Opening is used
(BTUH)
(sq inches)
50,000
75,000
100,000
125,000
150,000
specifies the minimum area for each of the 2 combustion air
openings and minimum round duct diameter for horizontal
METHOD 2:
ducting only.
One permanent opening located within 12 inches of the top of
the enclosure, shall be permitted where the equipment has
clearances of at least 1 inch from the sides and back and 6
inches from the front of the appliance. The opening shall di-
rectly communicate with the outdoors or communicate
through a vertical or horizontal duct to the outdoors or spaces
(crawl or attic) that freely communicate with the outdoors,
and shall have a minimum of:
FIGURE 10
NON-DIRECT VENT
AIR FROM
HEATED
SPACE
GAS
WATER
HEATER
FURNACE
HORIZONT L DUCT.
Round Pipe Duct
Diameter (inches)
25
6
38
8
50
8
63
10
75
10
VENT PENETRATIONS
FOR NON DIRECT VENT FURNACES
AIR FROM HEATED SPACE
12"
MAX
NOTE:
EACH OPENING SHALL
HAVE A FREE AREA OF
NOT LESS THAN ONE
SQUARE INCH PER
1,000 BTU PER HOUR OF
THE TOTAL INPUT
RATING OF ALL
EQUIPMENT IN THE
ENCLOSURE, BUT NOT
LESS THAN 100
SQUARE INCHES.
12"
MAX
ST-A1227-01
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