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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 Natural
Gas and Propane Installation Code, CAN/CSA B149.1, 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 allowable room
volume for all appliances in space. Use a different
method if minimum volume not available.
A. Standard Method. Cannot be used if known air
infiltration 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
B. Known Air Infiltration Rate. See Table 4 for
space with boiler only. Use equation for multiple
appliances. Do not use an air infiltration rate
(ACH) greater than 0.60.
Volume ≥ 21 ft
⁄ACH x Total Input [Mbh]
3
C. Refer to National Fuel Gas Code for opening
requirements between connected indoor spaces.
Table 3 - Minimum Room Volume, Indoor Air Only*
Standard
Input Mbh
Method
75
3750
112.5
5625
150
7500
187.5
9375
255
11250
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]
Known Air Infiltration Rate Method ACH (Air Changes Per Hour)
0.1
15750
23625
31500
39375
47250
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.
… 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).
• 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.
0.2
0.3
7875
5250
11813
7875
15750
10500
19688
13090
23625
15750
27563
18375
31395
20930
14
0.4
0.5
3938
3150
5906
4725
7875
6300
9844
7875
11813
9450
13781
11025
15698
12558
PN 240013090 REV. C [10/01/2021]
0.6
2625
3938
5250
6563
7875
9188
10465
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