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SECTION C: COMBUSTION AND VENTILATION AIR
COMBUSTION AND VENTILATION AIR (Indoor Units)
The boiler must be supplied with sufficient quantities of non-contaminated air to support proper combustion and equipment
ventilation. Combustion air can be supplied via conventional venting, where combustion air is drawn from the area immedi-
ately surrounding the boiler, or via direct vent, where combustion air is drawn directly from outside. All installations must
comply with the requirements of NFGC for U.S., CAN/CGA B 149.1 and .2 for Canada, and all local codes.
NOTICE: “In calculating free area, the required size of openings for combustion, ventilation, and dilution air shall be
based on net free area of each opening. If the free area through a design of louver or grill is known, it shall be used in
calculating the size opening required to provide the free area specified”. For additional information, refer to the latest
NFGC code requirements.
DIRECT COMBUSTION AIR
If outside air is drawn through a vent pipe directly to the unit for combustion:
1. Install combustion air direct vent in accordance with Section J of this manual.
2. Provide for adequate ventilation of the space occupied by the boiler(s) by an opening(s) for ventilation air at the
highest practical point communicating with the outdoors. The total cross sectional area shall be at least one (1)
square inch of free area per 20,000 BTUH of total input rating of all equipment in the room when the opening is
communicating directly with the outdoors or through vertical duct(s). The total cross sectional area shall be at least
one (1) square inch of free area per 10,000 BTUH of total input rating of all equipment in the room when the opening
is communicating with the outdoors through horizontal duct(s).
3. In cold climates, and to mitigate potential freeze-up, Raypak highly recommends the installation of a motorized
sealed damper to prevent the circulation of cold air through the boiler during the non-operating hours.
CAUTION: Remove the screen off the blower inlet and install a screen (1/2"-3/4" mesh) on the inlet elbow.
CONVENTIONAL COMBUSTION AIR SUPPLY (FOR U.S. INSTALLATION ONLY)
All Air from Inside the Building. If all combustion air is drawn from the air inside the building (the mechanical
equipment room does not receive air from outside):
1. The mechanical equipment room must be provided with two permanent openings communicating directly
with additional room(s) of sufficient volume so that the combined volume of all spaces meets the criteria for
an unconfined space. (An unconfined space is defined as a space whose volume is more than 50 cubic feet per
1,000 BTUH of the aggregate input rating of all appliances installed in that space.)
2. Each opening must have a minimum free area of one (1) square inch per 1,000 BTUH of the total input
rating of all gas utilization equipment in the mechanical equipment room.
3. One opening must commence within twelve (12) inches of the top, and one opening must commence within
twelve (12) inches of the bottom of the room.
4. Refer to NFGC, Part 5, for additional information.
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