4
FRESH AIR FOR COMBUSTION
!
WARNING
Air openings to combustion area must
not be obstructed. Following instructions
below, adequate combustion air can be
maintained.
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 infi ltration rate is 0.40 air changes per
hour. See Table 1 for space with boiler only.
Use equation for multiple appliances.
Volume ≥ 50 ft
3
x Total Input [Mbh]
Known Air Infi ltration Rate. See Table 1 B.
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
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 C.
requirements for louvers, grilles, screens and
air ducts.
Combination Indoor and Outdoor Air. Refer •
to National Fuel Gas Code for application
information.
Table 1 - Minimum Room Volume, Indoor Air Only*
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
37.5 1875 7875 3938 2625 1969 1575 1313
70 3500 14700 7350 4900 3675 2940 2450
105 5250 22050 11025 7350 5513 4410 3675
140 7000 29400 14700 9800 7350 5880 4900
175 8750 36750 17375 12250 9188 7350 6125
210 10500 44100 22050 14700 11025 8820 7350
245 12250 51450 25725 17150 12863 10290 8575
280 14000 58800 29400 19600 14700 11760 9800
* Table values based on boiler only. Add volume for any additional appliances.
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