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FIGURE 9: HORIZONTAL DIRECT EXHAUST VENT SYSTEM (VENT OPTIONS 4,5)
2) Maximum Vent and Air Intake Lengths - The maximum length of the vent air intake piping depends upon the vent option
selected, the vent pipe size, and the boiler size. See Table 3 for the maximum vent length. In addition to the maximum
length of piping shown in Table 3, the following fi ttings may also be used:
• Horizontal Vent Systems: One 90 deg. elbow
• Vertical Vent Systems: Two 90 deg. elbows
• Vertical Coaxial Vent Systems: Two 90 deg. elbows
• Air Intake Systems: Two 90 deg. elbows
If additional elbows are desired, the maximum allowable vent length must be reduced by the amount shown in Table 5 for
each additional elbow used. Note: Termination fi ttings do not need to be counted when counting additional elbows.
Example:
A 3” vent system is planned for a horizontal direct vented CWD165 which has the following components:
2 ft vertical pipe
1 90 elbow
5 ft horizontal pipe
1 90 elbow
3 ft horizontal pipe
1 45 elbow
4 ft horizontal pipe
1 termination elbow
The Vent Option #1 column in Table 3a describes a horizontal direct vent system using 3” vent pipe. From this column, we
see that a CWD165 may vent length of up to 35ft. The fi rst 90 elbow and the termination elbow are not considered. From
Table 5, the equivalent length of the 3” 45 elbow is 4ft and the equivalent length of the 3” 90 degree elbow is 5.5ft. The
maximum allowable run of straight pipe on this system is therefore:
35ft – 4 ft – 5.5ft = 25.5ft
Since the planned installation has only 14 ft of straight pipe, the planned vent length is acceptable.
3) Minimum Vent / Exhaust Pipe Length - Minimum vent length is 2ft. Minimum air inlet length is 0ft.