Flue and Combustion Air Venting
3-8
750-382
CBT
3.7 — Vertical venting, inside combustion air (Category III) central heating
These installations utilize the boiler mounted blower to vent the combustion products to the outside. Combustion
air is taken from inside the room and the vent is installed vertically through the roof to the outside. Adequate
combustion and ventilation air must be supplied to the boiler room in accordance with the National Fuel Gas
Code or, in Canada, the latest edition of CAN/CGA-B 149.1 AND.2. Installation Code for Gas Burning Appliances
and Equipment.
To prevent condensation accumulation in extended horizontal runs:
• It is required to install the horizontal portion of the flue venting with a slight downward slope of at least 1/8”
per foot of horizontal run.
• An approved condensate trap must be installed per applicable codes.
Flue Vent Termination
(velocity cone type)
If 10’-0”
or less
24”
Minimum
24”
Minimum
FIGURE 3-4. Vertical stack with inside combustion air
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