Unconfined Space; Confined Space; Using Indoor Air For Combustion; Using Outdoor Air For Combustion - Rinnai I Series Installation And Operation Manual

Unconfined Space

An unconfined space is defined in National Fuel Gas Code, ANSI Z223.1/NFPA 54 as "a space whose
volume is not 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. 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.

Confined Space

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." Examples include a small room, closet, alcove,
utility room, etc. 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.

Using Indoor Air For Combustion

When using air from other room(s) in the building, the total volume of the room(s) must be of
adequate volume (greater than 50 cubic feet per 1000 Btu/hr). Combustion air openings between
joining rooms must have at least 1 square inch of free area for each 1000 Btu/hr, but not less than
100 square inches each.

Using Outdoor Air For Combustion

Outdoor air can be provided to a confined space through two permanent openings, one
commencing within 12 in. (0.30 m) of the top and one commencing within 12 in. (0.30 m) of the
bottom, of the confined space. The openings shall communicate to the outside by one of two ways.
When communicating directly with the outdoors through horizontal ducts, each opening shall have
2 2
a minimum free area of 1 in /2000 Btu/hr (1100 mm /kW) of total input rating of all appliances in
the confined space.
Note: If ducts are used, the cross sectional area of the duct must be greater than or equal to the
required free area of the openings to which they are connected.
Louvers and Grills
When sizing the permanent opening 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 1/4 in.
2
Examples: Wood: 10 in. x 12 in. x 0.25 = 30 in.
2
Metal: 10 in. x 12 in. x 0.75 = 90 in.
42 Rinnai I-Series Condensing Boiler Combi Manual