Rinnai E75CN Installation & Servicing Instructions Manual page 44

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Confi ned Space:
(Small Room, Closet, Alcove, Utility Room, Etc.)
A confi ned space is defi ned in the 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 confi ned 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:
Using indoor air for combustion
Using outdoor air for combustion
Louvers and Grills
When sizing the permanent opening as illustrated in fi gure 17, 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:
Wood: 10 in x 12 in x 0.25 = 30 in2
Metal: 10 in x 12 in x 0.75 = 90 in2
Location
To maintain proper circulation of combustion air two permanent openings (one upper,
one lower) must be positioned in confi ned spaces. The upper shall be within 12 inches
of the confi ned space and the lower opening shall be within 12 inches of the bottom
of the confi ned space. Openings must be positioned as to never be obstructed.
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).
Gas Vent / Boiler Exhaust
OUTLET AIR DUCT
INLET AIR DUCT
Louvers and grills
BOILER
12in. MAX
BOILER
PERMANENT
OPENINGS
12in. MAX
12"
(300mm)
10"
(250mm)
figure 20