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8.1.4
CASE 4: FURNACE LOCATED IN A CONFINED SPACE,
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 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.
FIGURE 6 - OUTDOOR AIR FOR COMBUSTION,
HORIZONTAL (CASE 4)
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" ROUND PIPES TO
OBTAIN SUFFICIENT COMBUSTION AND VENTILATION AIR, THE DUCT COULD BE AN
EQUIVALENT RECTANGULAR DUCT; 8" X 7" FOR EXAMPLE. BASED ON 50% FREE AREA
FOR THE INLET GRILLS, THE ACTUAL GRILL SIZE WOULD HAVE TO BE 14" X 8" OR ITS
EQUIVALENT. A TRANSITION MAY BE USED TO REDUCE TO THE SMALLER DUCT SIZE
IF NECESSARY.
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
COMBUSTION AIR THROUGH THE TOP, OR A DOWNWARD
POINTING SINGLE ELBOW IF SUPPLYING COMBUSTION
AIR THROUGH THE SIDE. (FIGURE 7)
W415-1064 / 11.11.11
OUTDOOR AIR DUCTED HORIZONTALLY
TABLE 3 - HORIZONTAL AIR SUPPLY (CASE 4)
Input
Free Area
K/Btu/hr
Ea. Opening
60
30 in. ²
80
40 in. ²
100
50 in. ²
120
60 in. ²
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
Round Pipe Size
7 in.
8 in.
8 in.
9 in.
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