Model CFC ClearFire Commercial Boilers
55 Rev. 05-2012
Notice
Consult local codes, which may supersede these requirements.
Direct Vent
Combustion
If combustion air will be drawn directly from the outside by means of a duct
connected to the burner air intake, use the following as a guide:
1. Install combustion air vent (direct vent combustion) in accordance with the
boiler's Operating and Maintenance manual.
2. Provide for adequate ventilation of the boiler room or mechanical equipment
room.
3. In cold climates, and to mitigate potential freeze-up of the intake pipe, it is
highly recommended that a motorized sealed damper be used to prevent the
circulation of cold air through the boiler during non-operating hours.
4. Figure B5-49 shows the optional direct vent combustion kit providing easy
adaptation of the contractor supplied air duct to boiler connection. Refer to Table
B5-26 for sizing the direct vent combustion air pipe.
Figure B5-49. Optional Direct Vent Combustion Kit
STACK/BREECHING SIZE CRITERIA
General Boilers are divided into four categories based on the pressure and temperature
produced in the exhaust stack 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
the vent.
• Category III. A boiler which operates with a positive vent pressure and with 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 vent
gas temperature that may cause excessive condensate production in the vent.
Depending on the application, the Model CFC may be considered Category II, III,
or IV. The specifying engineer should dictate flue venting as appropriate to the
installation.
In some cases, PVC/CPVC material meeting ULC Type BH Class IIB specifications
may be used. Use of PVC/CPVC depends on operating conditions, specific vent
FAN/BLOWER
VENTURI
AIR SUPPLY LINE
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