17
Rev 2.1
3. The opening must have a minimum free area of 1 sq. in. per 3,000 BTUH of the total input rating of all equipment
in the room, or no less than the sum of the areas of all vent connectors in the confined space.
(For additional information, referred to the latest NFGC)
Warning: Do not use the “one permanent opening” method if the equipment room is under negative pressure conditions
or the equipment is common vented with other gas fired appliances.
Note:
Louvers and grilles. The required size of opening for combustion, ventilation and dilution air shall be based on the
net free area of each opening. Where free area through a design of louver or grille is known, it shall be used in calculating
the size opening required to provide the free area specified. Where the louver and grille design and free area are not
known, it shall be assumed that wood louvers will have 25% free area, and metal louvers and grilles will have 75% free
area (NFGC).
Canadian Installation
Caution: All combustion air must be drawn from the outside air of the building; the mechanical equipment room must
communicate directly with outdoor air.
1. Ventilation of the space occupied by the boiler shall be provided by an opening(s) for ventilation air at the highest
practical point communicating with the outdoors. The total cross-sectional area of such an opening(s) shall be at
least 10% of the area required in (2) below, but no less than 10 sq. in.
2. For boilers using a barometric damper vent system there shall be a permanent air supply opening(s) having a
cross section area of not less than 1 sq. in. per 7,000 BTUH up to and including 1 million BTUH, plus 1 sq. in. per
14,000 BTUH in excess of 1 million BTUH. This opening(s) shall be located at or ducted to a point no more than
18" nor less than 6" above floor level. The duct can also “goose neck” through the roof. The duct is preferred to be
straight down and terminated 18" from the floor, but not near the piping. This air supply opening requirement shall
be in addition to the air opening for ventilation air required in (1). (above)
3. For additional information, referred to CGA, B149
Warning: Care must be taken to ensure that the equipment room is not under negative pressure conditions.
2-6 Conventional Exhaust Venting
Caution: Proper installation of flue venting is critical for the safe and efficient operation of the boiler.
Definition of ANSI Categories for High Efficiency Appliances
Boilers are divided into four categories based on the pressure produced in the exhaust and the likelihood of condensate
production in the vent.
Category I
A boiler which operates with a non-positive vent static pressure and with a vent gas temperature that avoids
excessive condensate production in the vent.
Category II:
A boiler which operates with a non-positive vent static pressure and with a vent gas temperature that may
cause excessive condensate production in vent.
Category III:
A boiler which operates with a positive vent pressure and a vent gas temperature that avoids excessive
condensate production in the vent.
Category IV:
A boiler which operates with a positive vent pressure and with a gas temperature that may cause
excessive condensate production in the vent.
Note:
These definitions apply to the appliances and do not necessarily reflect the performance of the connected vent
system.
Note:
For additional information on appliance categorization, see appropriate ANSI Z21 Standard and the NFGC (US), or
CGA (Canada) B149, or applicable provisions of local building codes.
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