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6
50 CU. FT. OR MORE
PER 1000 BTU/HR. INPUT
ALL EQUIP. INSTALLED
UNCONFINED
AIR FOR COMBUSTION AND VENTILATION
If these furnaces are installed in a nondirect vent capacity
then the adequate flow of combustion and ventilating air
must not be obstructed from reaching the furnace. Air
openings provided for combustion air must be kept free of
obstructions which restrict the flow of air. Airflow restric-
tions affect the efficiency and safe operation of the furnace.
Keep this in mind should you choose to remodel or change
the area which contains your furnace. Furnaces must have a
free flow of air for proper performance.
Provisions for combustion and ventilation air shall be made
in accordance with latest edition of Section 5.3, Air for
Combustion and Ventilation, of the National Fuel Gas Code,
ANSI Z223.1 — CAN/CGA B149.1 or applicable provisions of
the local building codes. Special conditions created by
mechanical exhausting of air and fireplaces must be con-
sidered to avoid unsatisfactory furnace operation.
OUTSIDE AIR IS RECOMMENDED
The use of indoor air for most applications is acceptable,
unless there is the presence of corrosive chemicals or
contamination. Certain types of installation will require
the use of outside air for combustion.
The following types of installations will require use of
OUTDOOR AIR for combustion, due to chemical exposures:
* Commercial buildings
* Buildings with indoor pools
* Furnaces installed in "confined" laundry rooms
* Furnaces installed in "confined" hobby or craft rooms
* Furnaces installed near chemical storage areas.
Exposure to the following substances in the combustion 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
Furnace locations may be in a "confined space" or an
"unconfined space".
18-CD20D3-18
Installer's Guide
Unconfined space is defined in Figure 6. These spaces may
have adequate air by infiltration to provide air for combus-
tion and ventilation. Buildings with tight construction (for
example, weather stripping, heavily insulated, caulked, vapor
barrier, etc.), may need additional air to be provided as
described for confined space.
Confined spaces are installations with less than 50 cu. ft. of
space per 1000 BTU/hr input from all equipment installed.
Air for combustion and ventilation requirements can be
supplied from inside the building as in Figure 8 or from the
outdoors, as in Figure 9.
7
MINIMUM AREA IN SQUARE FEET
FOR UNCONFINED SPACE INSTALLATIONS
FURNACE
MAXIMUM BTUH
MINIMUM AREA IN SQUARE FEET
INPUT RATING
OF UNCONFINED SPACE
60,000
80,000
100,000
120,000
8
CONFINED
SPACE
1. All air from inside the building as in Figure 9: The
confined space shall be provided with two permanent
openings communicating directly with an additional
room(s) of sufficient volume so that the combined 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 Table 2 for minimum open areas
requirements.
2. All air from outdoors as in Figure 10: The confined space
shall be provided with two permanent openings, one
commencing within 12 inches of the top and one com-
mencing within 12 inches of the bottom of the enclosure.
The openings shall communicate directly, 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 requirements.
TABLE 2
MINIMUM FREE AREA IN SQUARE INCHES
EACH OPENING (FURNACE ONLY)
Furnace
Air
Maximum
From
BTUH/INPUT
Inside
Rating
60,000
100
80,000
100
100,000
100
120,000
120
WITH 8 FT. CEILING
375
500
625
875
Air From Outside
Vertical
Horizontal
Duct
Duct
15
30
20
40
25
50
30
60
7
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