Section 3 — Stack and Intake Vent Sizing and Installation
Part No. 750-363 3-3
Vent material should be appropriate for the Appliance Category.
Application-specific information will further determine the material
selected.
For Category II, III & IV appliance categories, Cleaver-Brooks highly
recommends that the flue system be Listed to standard UL 1738
Special Gas Vent and be installed in accordance with the National
Fuel Gas Code (NFPA 54) or ANSI Z21.47/ CSA 2.3. Type B Vent
shall not be allowed for positive pressure (forced draft burner) or
condensing vent systems.
Draft calculations should be performed for any condensing boiler
flue system. It is good practice to perform calculations at several
operating conditions to ensure draft tolerances are maintained.
For best performance, individual, through-the-roof vertical flue
venting is recommended for CFLC boilers. Cleaver-Brooks
recommends vertical straight flue (no loss) or velocity cone flue
termination.
Note:Traditional rain caps should not be used, as moist,
condensing flue gases can be directed downward
toward the building and air intakes. In cold climates and
freezing ambient temperatures, rain caps can lead to ice
formation, air intake blockage, and flue blockage that
result from condensing water vapor in the flue gases.
Cleaver-Brooks discourages the use of horizontal through-the-wall
flue termination with CFLC boilers. Vertical flue terminations are
recommended for optimum combustion performance and building
exterior maintenance.
An active draft inducer may be necessary for a horizontal flue
arrangement that exceeds the allowable draft tolerance.
Contact the Cleaver-Brooks authorized representative for
consideration of horizontal flue termination with CFLC boilers.
3.1.3 Draft Tolerances
For Individual flue vented boilers:
Maximum allowed pressure at vent connection is minus 0.25
inches to plus 0.10 to WC.
Recommended maximum design pressure at vent connection is
minus 0.10 to plus 0.10 inches WC.
For common flue vented boilers:
Maximum allowed pressure at vent connection is minus 0.25 inch
to 0.0 inch WC.
Recommended maximum design pressure at vent connection is
minus 0.10 to 0.0 inch WC.
3.1.4 Vent Terminal Location
Give special attention to the location of the vent termination to avoid
possibility of property damage, compromised performance, or
personal injury. For best results with condensing boilers, use vertical
straight (no loss) flue discharge or velocity cone termination. These
Figure 3-1 Vent Terminations
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