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." 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 Using outdoor air for combustion
Louvers and Grills
When sizing the permanent opening as illustrated in figure 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 up- per, 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.
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 ventila- tion fans).
Gas Vent / Boiler Exhaust |
OUTLET AIR DUCT
BOILER |
| 12in. MAX |
PERMANENT | BOILER |
| |
OPENINGS |
|
| 12in. MAX |
| 12" |
| (300mm) |
Instructions Rinnai
INLET AIR DUCT
Louvers and grills
10" |
(250mm) |
figure 17
Installation & Servicing
35
