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Model CFC
ClearFire Commercial Boilers
60
Rev. 05-2012
3. Combustion air supplied from the outside must be free of particulate and
chemical contaminants. To avoid a blocked flue condition, keep all the vent caps
clear of snow, ice, leaves, debris, etc.
Note: Multiple direct stack vent caps must not be installed with one combustion air inlet directly above
a stack vent cap. This vertical spacing would allow the flue products from the stack vent to be
pulled into the combustion air intake installed above. This type of installation can cause non-
warrantable problems with components and poor operation of the unit due to the recirculation of
flue products.
Table B5-25.
STACK DESIGN (SINGLE BOILER) USING ROOM AIR
ROOM COMBUSTION AIR -- MAXIMUM ALLOWABLE VENTING LENGTH
Boiler
Boiler Stack/Flue
Connection
Boiler
Flue/Stack
Size
Maximum length of
Flue Gas Vent in
Feet*
Flue Connection
Part No.
Room
Combustion Air
Required (CFM)
Air Filter Kit No.
(optional)
CFC 500
6" Standard
6"
80
039-01704
125
880-01858
CFC 750
6" Standard
6"
60
039-01704
190
880-01858
CFC1000
6" Option
6"
80
039-01646
250
880-01858
CFC1000
8" Standard
8"
140
039-01647
250
880-01858
CFC1000
10" Option
10"
200
039-01705
250
880-01858
CFC1500
8" Option
8"
60
039-01645
375
880-02005
CFC1500
10" Standard
10"
80
039-01644
375
880-02005
CFC1500
12" Option
12"
120
039-01688
375
880-02005
CFC1800
10" Option
10"
60
039-01644
450
880-02005
CFC1800
12" Standard
12"
100
039-01688
450
880-02005
CFC 2500
12" Standard
12"
110
039-01688
625
880-02005
CFC3300
12" Standard
12"
60
039-01761
800
880-02502
CFC3300
14" Option
14"
110
039-01762
800
880-02502
* Each additional 90 elbow equals 5 equivalent feet of ductwork. Flue terminations may add 5-10 feet
to the equivalent length and should also be included in the equivalent length calculation.
** Increasing the diameter of the air intake will reduce the overall pressure drop and thereby allow
longer total vent lengths.
Draft tolerance at boiler flue connection during operation is +/- 0.25” WC.