Section 3 — Stack and Intake Vent Sizing and Installation
Part No. 750-263 3-11
2. Stack design using direct vent combustion
Table 3-2 STACK SIZING USING OUTSIDE AIR FOR COMBUSTION
Boiler
Boiler Flue Connection Combustion Air
Duct
Connection
Maximum length of
Flue Gas Vent in
Feet*
Maximum length of
Air Intake Duct in
Feet**
CFC 500 6" Standard
4" 75 75
6" 80 80
CFC750 6" Standard
4" 40 40
6" 50 50
CFC1000
8" Standard 6" 60 60
6" Option 6" 40 40
10" Option 6" 80 80
CFC1500
10" Standard
6" 40 40
8" 60 60
8" Option
6" 30 30
8" 40 40
12" Option
6" 60 60
8" 80 80
CFC1800
12" Standard
6" 50 50
8" 80 80
10" Option
6" 40 40
8" 55 55
CFC 2500 12" Standard 8" 100 100
* Each additional 90 elbow equals 5 equivalent feet of ductwork. Subtract from the maximum
or minimum length accordingly.
** Increasing the diameter of the air intake will reduce the pressure drop and thereby allow
longer total vent lengths.
Maximum allowable pressure drop in combustion air intake duct is - 0.25" w.c.
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