6
3 - 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 jurisdictions.
• 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.
о
Standard Method. Cannot be used if known air
in
fi
ltration rate is less than 0.40 air changes per
hour. See Table 3 for space with boiler only. Use
equation for multiple appliances.
Volume
≥
50 ft
3
x Total Input [Mbh]
о
Known Air In
fi
ltration Rate. See Table 3 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]
о
Refer to National Fuel Gas Code for opening
requirements between connection indoor spaces.
• All Outdoor Air. Provide permanent opening(s)
communicating directly or by ducts with outdoors.
о
Two Permanent Opening Method. Provide opening
commencing within 12 inches of top and second
opening commencing within 12 inches of bottom
enclosure.
Direct communication with outdoors or
communicating through vertical ducts. Provide
minimum free area of 1 in
2
per 4 Mbh of total
input rating of all appliances in enclosure.
Communicating through horizontal ducts.
Provide minimum free area of 1 in
2
per 2
Mbh of total input rating of all appliances in
enclosure.
о
One Permanent Opening Method. Provide opening
commencing within 12 inches of top of enclosure.
Provide minimum clearance of 1 inch on sides
and 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 3 - Space With Boiler Only
Room Cubic Feet Volume
Input Mbh
Standard
Method
Known Air Infi ltration Rate Method (ACH - Air Changes Per Hour)
0.1
0.2
0.3
0.4
0.5
0.6
50
2500
10500
5250
3500
2625
2100
1750
75
3750
15750
7875
5250
3938
3150
2625
100
5000
21000
10500
7000
5250
4200
3500
125
6250
26250
13125
8750
6563
5250
4375
150
7500
31500
15750
10500
7875
6300
5250
170
8500
35700
17850
11900
8925
7140
5950
200
10000
42000
21000
14000
10500
8400
7000
