W415-1080 / B / 08.28.13
19
IOM
8.1.4 CASE 4: FURNACE LOCATED IN A CONFINED SPACE, OUTDOOR AIR
DUCTED HORIZONTALLY
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 (645 mm²) 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:
THE OUTDOOR GRILLS MUST BE INSTALLED IN A LOCATION WHERE THEY WILL NOT
BE OBSTRUCTED IN ANY MANNER.
FIGURE 7 - NON-DIRECT
COMBUSTION AIR INLET
8.1.5 CONNECTION TO FURNACE NON-DIRECT VENT
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 COM-
BUSTION AIR THROUGH THE TOP, OR A DOWNWARD
POINTING SINGLE ELBOW IF SUPPLYING COMBUSTION
AIR THROUGH THE SIDE.
(FIGURE 7)
TABLE 3 - HORIZONTAL AIR
SUPPLY (CASE 4)
Input
K/Btu/hr
Free Area
Ea. Opening
Round Pipe
Size
60
30 in
2
(194 cm
2
)
7 in
(178 mm)
80
40 in
2
(258 cm
2
)
8 in
(203 mm)
100
50 in
2
(323 cm
2
)
120
60 in
2
(387 cm
2
)
9 in
(229 mm)
H12.9.2
Combustion Air
Duct Terminates
12” (305mm)
above floor.
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” (203 mm) ROUND PIPES TO
OBTAIN SUFFICIENT COMBUSTION AND VENTILATION AIR, THE DUCT COULD BE AN
EQUIVALENT RECTANGULAR DUCT; 8” X 7” (203 mm X 178 mm) FOR EXAMPLE. BASED
ON 50% FREE AREA FOR THE INLET GRILLS, THE ACTUAL GRILL SIZE WOULD HAVE
TO BE 14” X 8” (356 mm X 203 mm) OR ITS EQUIVALENT. A TRANSITION MAY BE USED
TO REDUCE TO THE SMALLER DUCT SIZE IF NECESSARY.
