Rinnai RH180, Installation Fundamentals

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Unconfined space:
An unconfined space is defined in NFPA 54 as “a space whose volume is not less
than 50 cubic feet per 1,000 Btu/hr. (4.8 m
3
per kW per hour) of the aggregate input
rating of all appliances in that space. Rooms communicating directly with the space
in which the appliances are installed, through openings not furnished with doors, are
considered a part of the unconfined space”. If the “unconfined space” containing the
appliance(s) is in a building with tight construction, additional outside air may be
required for proper operation. Outside air openings should be sized the same as for
a confined space.
Vent Guidelines: Combustion air
Confined space:
(Small room, Closet, Alcove, Utility Room, Etc.)
A confined space is defined 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”.