CleaverBrooks ClearFire CFH, Operation, Service And Parts Manual

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Chapter 3 — Flue and Combustion Air Venting
Part No. 750-295 3-13
Figure 3-10 Direct vent combustion
3.10-MAXIMUM VENT LENGTHS
Based on horizontal venting. Size flues based on design draft calculations. Maximum allowable draft
tolerance is +/- 0.25" w.c. Recommended design draft tolerance for individual vented flues at +/- 0.10"
w.c.
Maximum combustion air pressure drop is 0.25" w.c.
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.
Draft tolerance at boiler flue connection during operation is +/-0.25” W.C.; Use +/-0.10” when designing venting system.
*Maximum vent length assumes horizontal run and sidewall terminations. Larger diameter venting, vertical flue runs, and vertical flue termination may allow for longer vent
lengths than indicated here, provided the engineered draft calculations are within the allowable operational tolerance of +/-0.25” W.C.
Boiler Size HP
Stack Connection - Flue
diameter (in)
Maximum Flue
Length (ft)*
Combustion Air Duct
diameter (in)
Maximum Air Intake
Length (ft)
10 6 150 4 150
15 6 80 4 80
20 6 80 4 80
25 6 70 4 70
30 8 100 6 100
40 8 40 6 40
50 10 60 8 60
60 10 60 8 60
70 12 80 8 80
80 12 80 8 80
Air Intake (w/ Screen)
Flue Gas Vent (w/ Screen)
48"
Minimum
12"
Minimum
48" Minimum
ClearFire ® Boiler