18-CD33D1-4
9
Installer’s Guide
6
MINIMUM AREA IN SQUARE FEET
FOR UNCONFINED SPACE INSTALLATIONS
FURNACE MAXI-
MUM BTUH INPUT
RATING
WITH 8 FT. CEILING
MINIMUM AREA IN SQUARE FEET
OF UNCONFINED SPACE
60,000
80,000
100,000
120,000
375
500
625
875
1. All air from inside the building as in Figure 8: The
confined space shall be provided with two perma-
nent openings communicating directly with an addi-
tional room(s) of sufficient volume so that the com-
bined volume of all spaces meets the criteria for an
unconfined space. The total input of all gas utilization
equipment installed in the combined space shall be
considered in making this determination. Refer to Ta-
ble 2 for minimum open areas requirements.
2. All air from outdoors as in Figure 9: The confined
space shall be provided with two permanent open-
ings, one commencing within 12 inches of the top
and one commencing within 12 inches of the bottom
of the enclosure. The openings shall communicate di-
rectly, or by ducts, with the outdoors or spaces (crawl
or attic) that freely communicate with the outdoors.
Refer to Table 2, for minimum open areas require-
ments.
TABLE 2
MINIMUM FREE AREA IN SQUARE INCHES
EACH OPENING (FURNACE ONLY)
Furnace
Maximum
BTUH/INPUT
Rating
Air
From
Inside
Air From Outside
Vertical
Duct
Horizontal
Duct
40,000
60,000
80,000
97,000
110,000
100
100
100
100
110
10
15
20
25
28
20
30
40
50
55
CONFINED
SPACE
7
8
9
