BOILER BOOK CFC-E ENGINEERING DATA
34
Boiler Room Combustion and Ventilation Air
The boiler(s) must be supplied with adequate quantities of uncontaminated air to support proper
combustion and equipment ventilation. Air shall be free of chlorides, halogens, fluorocarbons,
construction dust or other contaminants that are detrimental to the burner/boiler. If these
contaminants are present, we recommend the use of direct vent combustion provided the outside air
source is uncontaminated.
Combustion air can be supplied by means of conventional venting, where combustion air is drawn
from the area immediately surrounding the boiler (boiler room must be positive pressure), or with
direct vent (direct vent combustion) where air is drawn directly from the outside. All installations
must comply with local Codes and with NFPA 54 (the National Fuel Gas Code - NFGC) for the U.S.
and for Canada, CAN/CGA B 149.1 and B 149.2.
Note: A boiler room exhaust fan is not recommended as this type of device can cause a negative pressure in the boiler room
if using a conventional air intake.
In accordance with NFPA54, the required volume of indoor air shall be determined in accordance
with the “Standard Method” or “Known Air Infiltration Rate Method. Where the air infiltration rate is
known to be less than 0.40 Air Changes per Hour, the Known Air Infiltration Rate Method shall be
used. (See Section 8.3 in the NFPA54 Handbook for additional information.)
Combustion Air Supply - Unconfined Spaces (For U.S. Installations Only)
A. All Air From Inside the Building - If additional combustion air is drawn from inside the
building (the mechanical equipment room does not receive air from outside via louvers or vent
openings and the boiler is not equipped with direct vent combustion) and the boiler is located
in a unconfined space, use the following guidelines:
1. The mechanical equipment room must be provided with two permanent openings linked
directly with additional room (s) of sufficient volume so that the combined volume of all
spaces meet the criteria for an unconfined space. Note: An “unconfined space” is defined
as a space whose volume is more than 50 cubic feet per 1,000 Btu per hour of aggregate
input rating of all appliances installed in that space.
2. Each opening must have a minimum free area of one square inch per 1,000 Btu per hour
of the total input rating of all gas utilizing equipment in the mechanical room.
3. One opening must terminate within twelve inches of the top, and one opening must
terminate within twelve inches of the bottom of the room.
4. Refer to the NFGC, Section 8.3 for additional information.
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