W415-0973 / B / 08.28.13
18
IOM
IOM
8.1.4 CASE 4: FURNACE LOCATED IN A CONFINED SPACE, OUTDOOR AIR
DUCTED HORIZONTALLY
8.1.5 CONNECTION TO FURNACE NON-DIRECT VENT
H13.4
Similar to Case 3, outdoor air for combustion and ventilation may be drawn through horizontal ducting. The
free area for each opening is calculated on the basis of a minimum of 1 square inch (645mm²) per 2000 Btu/hr
input.
The following table shows minimum free areas and round pipe sizes when drawing combustion air horizontally
from the outdoors for the furnace only. If other fuel burning appliances are present, their combustion air and
ventilation air requirements must be added to those of the furnace.
IMPORTANT:
IF GRILLS ARE USED ON THE OUTSIDE WALL, THEY MUST BE SIZED PROPERLY.
MOST SIDEWALL GRILLS HAVE ONLY 50% FREE AREA. IN THE CASE OF A UNIT WITH
100,000 BTU/HR INPUT, WHICH REQUIRES A PAIR OF 8” (203mm) ROUND PIPES TO
OBTAIN SUFFICIENT COMBUSTION AND VENTILATION AIR, THE DUCT COULD BE AN
EQUIVALENT RECTANGULAR DUCT; 8” X 7” (203mm X 178mm) FOR EXAMPLE. BASED
ON 50% FREE AREA FOR THE INLET GRILLS, THE ACTUAL GRILL SIZE WOULD HAVE
TO BE 14” X 8” (356mm X 203mm) OR ITS EQUIVALENT. A TRANSITION MAY BE USED TO
REDUCE TO THE SMALLER DUCT SIZE IF NECESSARY.
IMPORTANT:
THE OUTDOOR GRILLS MUST BE INSTALLED IN A LOCATION WHERE THEY WILL NOT BE
OBSTRUCTED IN ANY MANNER.
Combustion Air
Duct Terminates
12” (305mm)
above oor.
FIGURE 6 - OUTDOOR AIR FOR COMBUSTION,
HORIZONTAL (CASE 4)
TABLE 3 - HORIZONTAL AIR
SUPPLY (CASE 4)
Input
K/Btu/hr
Free Area
Ea. Opening
Round Pipe
Size
45
30 in
2
(194cm
2
)
7 in
(178mm)
60
80
40 in
2
(258cm
2
)
8 in
(203mm)
100
50 in
2
(323cm
2
)
120
60 in
2
(387cm
2
)
9 in
(229mm)
H12.9.3
H13.5
FIGURE 7 - NON-DIRECT
COMBUSTION AIR INLET
IMPORTANT:
WHEN USING INDOOR AIR OR THE NON-DIRECT
VENT CONFIGURATION, THE COMBUSTION AIR
INLET TO THE FURNACE MUST BE PROTECTED
FROM BLOCKAGE. USE A DOUBLE ELBOW
ARRANGEMENT IF SUPPLYING COMBUSTION AIR
THROUGH THE TOP, OR A DOWNWARD POINTING
SINGLE ELBOW IF SUPPLYING COMBUSTION AIR
THROUGH THE SIDE. (FIGURE 7)
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