12
FRESH AIR FOR COMBUSTION
WARNING
Air openings to combustion area must not be
obstructed. Follow instructions below, to maintain
adequate 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.
A. Standard Method. See Table 3 for
space with natural gas boiler only. For
multiple appliances and/or propane:
Room Volume must be greater than 50 cubic feet
multiplied by Total Input [Mbh]
B.
Known Air Infiltration Rate. See Table 3 for
space with boiler only. Use equation for multiple
appliances. Do not use an air infiltration rate air
changes per hour (ACH) greater than 0.60.
Room volume shall be greater than
21 cubic feet
divided by ACH (air changes per hour) x Total Input
[Mbh]
C. Refer to National Fuel Gas Code for opening
requirements between connected indoor spaces.
•
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.
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.
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).
C. 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 3 - Minimum Room Volume, Indoor Air Only*
Input Mbh
Standard
Method
Known Air Infiltration Rate Method (Air Changes Per Hour)
0.1
0.2
0.3
0.4
0.5
0.6
75
3750
15750
7875
5250
3938
3150
2625
112.5
5625
23625
11813
7875
5906
4725
3938
150
7500
31500
15750
10500
7875
6300
5250
187
9350
39270
19635
13090
9818
7854
6545
225
11250
47250
23625
15750
11813
9450
7875
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.
PN 14683003 Rev. O [10/01/2021]
