Rinnai RH180 Operation And Installation Manual page 14

Combustion Air Requirements
Confined Space:
(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:
Louvers and Grills
When sizing the permanent opening as illustrated in
Figure 1, 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 in
Metal: 10 in x 12 in x 0.75 = 90 in
Location
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 inches of the confined space and the lower
opening shall be within 12 inches of the bottom of the
confined space. Openings must be positioned as to
never be obstructed.
Using Outdoor Air For Combustion
Outdoor air can be provided to a confined space
Combustion air provided to the appliance
should not be taken from any area of the
structure that may produce a negative pres-
sure (i.e. exhaust fans, powered ventilation
fans).
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RH180 Manual
Figure 1