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TYPICAL DOWNFLOW/HORIZONTAL ATTIC INSTALLATION
TYPICAL SUSPENDED FURNACE
AIR FOR COMBUSTION AND VENTILATION
Adequate flow of combustion and ventilating air must not be
obstructed from reaching the furnace. Air openings provided in
the furnace casing must be kept free of obstructions that restrict
the flow of air. Airflow restrictions 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. Fur-
naces 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, or
Sections 7.2, 7.3 or 7.4 of CAN/CGA B149 Installation Codes, and
applicable provisions of the local building codes. Special condi-
tions created by mechanical exhausting of air and fireplaces must
be considered to avoid unsatisfactory furnace operation.
Furnace locations may be in "confined space" or "unconfined
space". Unconfined space is defined in Table 2 and Figure 7.
These spaces may have adequate air by infiltration to provide air
for combustion, ventilation, and dilution of flue gases. Buildings
with tight construction (for example, weather stripping, heavily
insulated, caulked, vapor barrier, etc.), may need additional air
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 9 or from the outdoors, as in
Figures 10 & 11.
Pub. No. 41-5010-20
FIGURE 5
FIGURE 6
Installation Instructions
50 CU. FT. OR MORE
PER 1000 BTU/HR. INPUT
ALL EQUIP. INSTALLED
UNCONFINED
CONFINED
LESS THAN 50 CU. FT.
PER 1000 BTU/HR. INPUT
ALL EQUIP INSTALLED
1. All air from inside the building as in Figure 9: The confined
space shall be provided with two permanent openings communi-
cating 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 equip-
ment 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 Figures 10 & 11: The confined
space shall be provided with two permanent openings, one com-
mencing within 12 inches of the top and one commencing 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 3, for minimum open areas required.
3. 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 commercial laundry rooms
* Furnaces installed in 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
FIGURE 7
FIGURE 8
Page 7
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