6
5 - VENTILATION & COMBUSTION AIR
Provide combustion air and ventilation air in accordance
with the section “Air for Combustion and Ventilation,”
of the National Fuel Gas Code, ANSI Z223.1/NFPA 54 or
applicable provisions of local building codes.
Provide make-up air where exhaust fans, clothes
dryers, and kitchen ventilation equipment interfere
with proper operation.
National Fuel Gas Code recognizes several methods
of obtaining adequate ventilation and combustion air.
Requirements of the authority having jurisdiction may
override these methods.
Engineered Installations. Must be approved by
•
authority having jurisdiction.
Mechanical Air Supply. Provide minimum of
•
0.35 cfm per Mbh for all appliances located
within space. Additional requirements where
exhaust fans installed. Interlock each appliance
to mechanical air supply system to prevent main
burner operation when mechanical air supply
system not operating.
All Indoor Air. Calculate minimum volume for all
•
appliances in space. Use a different method if
minimum volume not available.
Standard Method. Cannot be used if known
A.
air in
fi
ltration rate is less than 0.40 air
changes per hour. See Table 4 for space
with boiler only. Use equation for multiple
appliances.
Volume
≥
50 ft
3
x Total Input [Mbh]
Known Air In
fi
ltration Rate. See Table 4
B.
for space with boiler only. Use equation
for multiple appliances. Do not use an air
in
fi
ltration rate (ACH) greater than 0.60.
Volume
≥
21 ft
3
⁄
ACH x Total Input [Mbh]
Refer to National Fuel Gas Code for opening
C.
requirements between connected indoor
spaces.
All Outdoor Air. Provide permanent opening(s)
•
communicating directly or by ducts with outdoors.
Two Permanent Opening Method. Provide
A.
opening commencing within 12 inches of top
and second opening commencing within 12
inches of bottom of enclosure.
Direct communication with outdoors or
communicating through vertical ducts.
Provide minimum free area of 1 in² per 4
Mbh of total input rating of all appliances
in enclosure.
Communicating through horizontal ducts.
Provide minimum free area of 1 in² per 2
Mbh of total input rating of all appliances
in enclosure.
One Permanent Opening Method. Provide
B.
opening commencing within 12 inches of top
of enclosure. Provide minimum clearance of
1 inch on sides/back and 6 inches on front
of boiler (does not supersede clearance to
combustible materials).
Refer to National Fuel Gas Code for additional
•
requirements for louvers, grilles, screens and air
ducts.
Combination Indoor and Outdoor Air. Refer
•
to National Fuel Gas Code for application
information.
Table 4 - Minimum Room Volume, Indoor Air Only*
Room Cubic Feet Volume
Input
Mbh
Standard
Method
Known Air Infi ltration Rate Method (Air Changes Per Hour)
0.1
0.2
0.3
0.4
0.5
0.6
262.5
13125
55125
27563
18375
13781
11025
9188
299
14950
62790
31395
20930
15698
12558
10465
* Table values based on boiler only. Add volume for any additional appliances.
