Flue and Combustion Air Venting
3-6
750-382
CBT
3.5 — Horizontal through-wall direct venting
These installations utilize the boiler mounted blower to draw combustion air from outside and vent combustion
gases to the outside.
Combustion air venting can be constructed of steel, stainless steel, PVC, CPVC, or material as deemed appropri-
ate for the application and per local codes. The direct vent air intake should be considered in the overall length
calculation of the venting system.
Care must be taken during assembly that all joints are sealed properly and are airtight for both the combustion
air intake and the exhaust flue piping system.
The flue venting must be installed to prevent the potential accumulation of condensate in the stack pipes. It is
recommended that:
1. Vent be installed with a slight downward slope of at least 1/8” per foot of horizontal run to the stack terminal.
2. The flue venting is to be insulated through the length of the horizontal run.
For appliances installed in extreme cold climate, it is recommended that:
FIGURE 3-3. Horizontal through-wall direct venting system, Category
III installation
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