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.
Standard Method. Cannot be used if known air о
inltration 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 ft3 x Total Input [Mbh]
Known Air Inltration Rate. See Table 3 for о
space with boiler only. Use equation for multiple
appliances. Do not use an air inltration rate
(ACH) greater than 0.60.
Volume ≥ 21 ft3/ACH x Total Input [Mbh]
Refer to National Fuel Gas Code for opening о
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 о
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 in2 per 2
Mbh of total input rating of all appliances in
enclosure.
One Permanent Opening Method. Provide opening о
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).
Combination Indoor and Outdoor Air. Refer to о
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 pro-
viding 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).
Section 8.4 when combination of appliances has total •
input exceeding 400 Mbh (120 kW).
Refer to Natural Gas and Propane Installation Code •
for specic air supply requirements for enclosure
or structure where boiler is installed, including air
supply openings and ducts.
Table 3
Input Mbh Standard
Method Known Air Inltration Rate Method (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
175 8750 36750 18375 12250 9188 7350 6125
200 10000 42000 21000 14000 10500 8400 7000
250 12500 52500 26250 17500 13125 10500 8750
300 15000 63000 31500 21000 15750 12600 10500
