Room And Indoor Combustion Ventilation Requirements - Westinghouse WBMC**500 Manual

2. Room and Indoor Combustion Ventilation Requirements

When using an indoor combustion air installation, the
mechanical room MUST be provided with properly sized
openings, and/or be of sufficient volume to assure adequate
combustion air and proper ventilation for all gas fired appliances
in the mechanical room to assure adequate combustion air and
proper ventilation. The requirements shown here are for the
boiler only. Additional gas fired appliances in the mechanical
room will require an increase in the net free area and/or
volume to supply adequate combustion air for all appliances.
This must be done in accordance with the National Fuel Gas
Code, NFPA 54 / ANSI Z223.1.
This boiler can be vented using mechanical room air only for
combustion. No combustion air openings are needed when
the boiler is installed in a space with a volume NO LESS than 50
cubic feet per 1,000 BTU/hr of all installed gas fired appliances
and the building MUST NOT BE of "Tight Construction".
TIGHT CONSTRUCTION: A building with less than .4 ACH
(air changes per hour). For buildings of "Tight Construction",
provide air openings into the building from the outside.
Indoor and outdoor combustion air may be combined by
applying a ratio of available volume to required volume times
the required outdoor air opening(s) size(s). This must be done
in accordance with the National Fuel Gas Code, NFPA 54 /
ANSI Z223.1.
1. If air is taken directly from outside the building with no duct,
provide two permanent openings to the mechanical room
each with a net free area of one square inch per 4000 BTU/hr
input. See Figure 17.
2. If combustion and ventilation air is taken from the outdoors
using a duct to deliver the air to the mechanical room, each of
the two openings should be sized based on a minimum free
area of one square inch per 2000 BTU/hr input. See Figure 18.
3. If air is taken from another interior space combined with the
mechanical room:
a. Two spaces on same story: Each of the two openings
specified should have a net free area of one square inch for
each 1000 BTU/hr input, but not less than 100 square inches.
b. Two spaces on different stories: One or more openings
should have a net free area of two square inches per 1000
BTU/hr.
See Figure 19 for reference.
4. If a single combustion air opening is provided to bring
combustion air in directly from the outdoors, the opening
must be sized based on a minimum free area of one square
inch per 3000 BTU/hr. This opening must be located within 12"
of the top of the enclosure. See Figure 20.
Combustion air requirements are based on the latest edition
of the National Fuel Gas Code, NFPA 54 / ANSI Z223.1, CGA
Standard CAN/CSA B149.1 in Canada. Check all local code
requirements for combustion air.
All dimensions based on net free area in square inches. Metal
louvers or screens reduce the free area of a combustion air
opening a minimum of approximately 25%. Check with louver
manufacturers for exact net free area of louvers.
Where two openings are provided, one must be within 12"
of the ceiling, and one must be within 12"of the floor of the
mechanical room. Each opening must have a net free area as
specified in Table 11. Single openings shall commence within
12" of the ceiling. The minimum dimension of air openings
should not be less than 3".
Figure 17 - Combustion Air from Outdoors
Figure 18 - Combustion Air through Ductwork
Figure 19 - Combustion Air from Indoors
Figure 20 - Combustion Air from Outdoors - Single Opening
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WHL-033 Rev. 1.29.16