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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.
A.
Standard Method. Cannot be used if known
air infi 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
B.
Known Air Infi ltration Rate. See Table 4
for space with boiler only. Use equation
for multiple appliances. Do not use an air
infi ltration rate (ACH) greater than 0.60.
Volume ≥ 21 ft
C.
Refer to National Fuel Gas Code for opening
requirements between connected indoor
spaces.
Table 4 - Minimum Room Volume, Indoor Air Only*
Input
Standard
Mbh
Method
262.5
13125
299
14950
* Table values based on boiler only. Add volume for any additional appliances.
5 - VENTILATION & COMBUSTION AIR
x Total Input [Mbh]
3
⁄ACH x Total Input [Mbh]
3
Known Air Infi ltration Rate Method (Air Changes Per Hour)
0.1
55125
62790
•
All Outdoor Air. Provide permanent opening(s)
communicating directly or by ducts with outdoors.
A.
Two Permanent Opening Method. Provide
opening commencing within 12 inches of top
and second opening commencing within 12
inches of bottom of enclosure.
B.
One Permanent Opening Method. Provide
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.
Room Cubic Feet Volume
0.2
0.3
27563
18375
31395
20930
6
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.
0.4
0.5
13781
11025
15698
12558
0.6
9188
10465
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