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6
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 Sections
8.2, 8.3 or 8.4 of 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 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
infi 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 Infi ltration Rate. See Table 3 for
space with boiler only. Use equation for multiple
appliances. Do not use an air infi ltration rate
(ACH) greater than 0.60.
Volume ≥ 15 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).
о Combination Indoor and Outdoor Air. 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.
National Gas and Propane Installation Code Requires
providing air supply in accordance with:
• Section 8.2 and 8.3 when combination of appliances
has a total input of up to and including 400 Mbh (120
kW).
о Does not have draft control device.
• Section 8.4 when combination of appliances has total
input exceeding 400 Mbh (120 kW).
• Refer to Natural Gas and Propane Installation Code
for specifi c air supply requirements for enclosure
or structure where boiler is installed, including air
supply openings and ducts.
Table 3- Air Infi ltration Rate
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
42.5 2125 6375 3188 2125 1594 1275 1063
75 3750 11250 5625 3750 2813 2250 1875
112.5 5625 16875 8438 5625 4219 3375 2813
150 7500 22500 11250 7500 5625 4500 3750
187.5 9375 28125 14063 9375 7031 5625 4688
225 11250 33750 16875 11250 8438 6750 5625