7
COMBUSTION AND VENTILATION AIR
!
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 air A.
infi ltration rate is less than 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 for B.
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 opening A.
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 opening B.
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 3 - Minimum Room Volume, Indoor Air Only*
Input Mbh
Standard
Method
Known Air Infi ltration Rate Method (Air Changes Per Hour)
0.1 .02 .03 .04 .05 .06
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 18375 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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