Section 3 — Stack and Intake Vent Sizing and Installation
3-2 Part No. 750-363
Notice
3.1 VENTING CONNECTIONS - GENERAL
3.1.1 Appliance Categories
Proper installation of flue gas exhaust venting is critical for efficient,
reliable, and safe operation of the CFLC boiler. The boiler’s
appliance category is a major factor determining venting system
design.
Definitions:
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 CFLC may be considered
Category II, III, or IV. The specifying engineer should dictate flue
venting as appropriate to the installation. CFLC condensing
applications will typically utilize Category IV venting.
For additional information on boiler
categorization, see appropriate
ANSI Z21 Standard and the latest
edition Standard of National Fuel
Gas Code or in Canada, the latest
edition of CSA Standard B149
Installation Code for Gas Burning
Appliances and Equipment, or
applicable provisions of local
building codes.
3.1.2 Flue Venting System Design
The flue venting should be supported to maintain proper clearances
from combustible materials.
Flue venting should be supported by the building structure. The
maximum load that the boiler flue connection can support is 500
lbs.
Use insulated vent pipe spacers where the vent passes through
combustible roofs and walls.
!
Warning
Contact the manufacturer of the vent material if there is any
question about the boiler categorization and suitability of a vent
material for application on a Category II, III or IV vent system.
Using improper venting materials can result in personal injury,
death or property damage.
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