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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 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.
Standard Method. Cannot be used if known air
infiltration 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]
Known Air Infiltration Rate. See Table 3 for
space with boiler only. Use equation for multiple
appliances. Do not use an air infiltration rate
(ACH) greater than 0.60.
Volume > 15 ft3/ACH x Total Input [Hbh]
o 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.
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 in2 per 4 Mbh of total
input rating of all appliances in enclosure.
Communicating through horizontal ducts.
Provide minimum free area of 1 in _ per 2
Mbh of total input rating of all appliances in
enclosure.
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).
o 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).
o 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 specific air supply requirements for enclosure
or structure where boiler is installed, including air
supply openings and ducts.
Table 2- Air Infiltration
Standard Known Air Infiltration Rate Method (Air Changes Per Hour)
Input Mbh Method 0,1 0,2 0,3 0,4 0,5 0,6
42,5 2125 6375 3188 2125 1594 1275 1063
75
112,5
150
187,5
225
3750
5625
7500
9375
11250
11250
16875
22500
28125
33750
5625
8438
11250
14063
16875
3750
5625
7500
9375
11250
2813
4219
5625
7031
8438
2250
3375
4500
5625
6750
1875
2813
3750
4688
5625
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