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Installer’s Guide
18-CD21D1-5 9
1. All air from inside the building as in Figure 9: 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 utiliza-
tion equipment installed in the combined space
shall be considered in making this determination.
Refer to Table 3, for minimum open areas required.
2.
All air from outdoors as in Figure 10: 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 bot-
tom of the enclosure. The openings shall communi-
cate directly, or by ducts, with the outdoors or
spaces (crawl or attic) that freely communicate with
the outdoors. Refer to Table 3, for minimum open
areas required.
3. The following types of installations will require use of
OUTDOOR AIR for combustion, due to chemical expo-
sures:
* Commercial buildings
* Buildings with indoor pools
* Furnaces installed in commercial laundry rooms
* Furnaces installed in hobby or craft rooms
* Furnaces installed near chemical storage areas.
Exposure to the following substances in the combus-
tion air supply will also require OUTDOOR AIR for
combustion:
* Permanent wave solutions
* Chlorinated waxes and cleaners
* Chlorine based swimming pool chemicals
* Water softening chemicals
* Deicing salts or chemicals
* Carbon Tetrachloride
* Halogen type refrigerants
* Cleaning solvents (such as perchloroethylene)
* Printing inks, paint removers, varnish, etc.
* Hydrochloric acid
* Cements and glues
* Antistatic fabric softeners for clothes dryers
* Masonry acid washing materials
TABLE 2
MINIMUM AREA IN SQUARE FEET FOR
UNCONFINED SPACE INSTALLATIONS
FURNACE MAXIMUM
BTUH / INPUT RATING
WITH 8 FOOT CEILING
MINIMUM AREA IN SQUARE FEET
OF UNCONFINED SPACE
40,000
60,000
80,000
100,000
120,000
140,000
250
375
500
625
750
875
TABLE 3
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
100,000
120,000
140,000
100
100
100
100
120
140
10
15
20
25
30
35
20
30
40
50
60
70
0
9