5 - 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
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 allowable room volume for all appliances in space. Use a different method if minimum volume not available.
A.Standard Method. Cannot be used if known air infiltration rate is less than 0.40 air changes per hour. See Table 4 for space with boiler only. Use equation for multiple appliances.
Volume ≥ 50 ft3 x Total Input [Mbh]
B.Known Air Infiltration Rate. See Table 4 for space with boiler only. Use equation for multiple appliances. Do not use an air infiltration rate (ACH) greater than 0.60.
Volume ≥ 21 ft3⁄ACH x Total Input [Mbh]
C.Refer to National Fuel Gas Code for opening requirements between connected indoor spaces.
•All Outdoor Air. Provide permanent opening(s) communicating directly or by ducts with outdoors.
A.Two Permanent Opening Method. Provide 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.
B.One Permanent Opening Method. Provide 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 requirements for louvers, grilles, screens and air ducts.
•Combination Indoor and Outdoor Air. Refer to National Fuel Gas Code for application information.
Canada
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).
•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 4 - Minimum Room Volume, Indoor Air Only*
|
|
|
| Room Cubic Feet Volume |
|
| ||
Input Mbh | Standard |
| Known Air Infiltration Rate Method (Air Changes Per Hour) |
| ||||
Method | 0.1 |
| 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | |
|
| |||||||
262.5 | 13125 | 55125 |
| 27563 | 18375 | 13781 | 11025 | 9188 |
299 | 14950 | 62790 |
| 31395 | 20930 | 15698 | 12558 | 10465 |
* Table values based on boiler only. Add volume for any additional appliances.
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