Demand Duo
™
R
-
Series Installation and Operation Manual
22
Combustion air provided to the appliance
should not be taken from any area of the
structure that may produce a negative
pressure (i.e. exhaust fans, powered
ventilation fans).
(Small Room, Closet, Alcove, Utility Room, Etc.)
A confined space is defined in the
National Fuel
Gas Code, ANSI Z223.1/NFPA 54
as "a space
whose volume is less than 50 cubic feet per 1000
Btu/hr (4.8 m3 per kW per hour) of the aggregate
input rating of all appliances installed in that
space." A confined space must have two
combustion air openings. Size the combustion air
openings based on the BTU input for all gas
utilization equipment in the space and the method
by which combustion air is supplied.
When sizing the permanent opening as illustrated
in Figure 12, consideration must be taken for the
design of the louvers or grills to maintain the
required free area required for all gas utilizing
equipment in the space. If the free area of the
louver or grill design is not available, assume
wood louvers will have 25% free area and metal
louvers or grills will have 75% free area. Under no
circumstance should the louver, grill or screen
have openings smaller than ¼
”.
Example:
Free Area = Height x Length x % free area
Wood: 18 in x 24 in x 0.25 = 108 in
2
Metal: 18 in x 24 in x 0.75 = 324 in
2
To maintain proper circulation of combustion air
two permanent openings (one upper, one lower)
must be positioned in confined spaces. The upper
shall be within 12 in. (300 mm) of the confined
space and the lower opening shall be within 12 in.
(300 mm) of the bottom of the confined space.
Openings must be positioned as to never be
obstructed.
24 in. (600 mm)
18 in.
(450 mm)
Note: 8 ft. ceiling
Figure 11
Figure 12
Figure 13
12 in.
(300 mm)
12 in.
(300 mm)
