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Example: A 100MBH model is to be installed as using Vent Option 34 in a masonry chimney as shown in Figure 7.23. The
following components are used:
Vent:
3” DuraVent Poly-Pro (Rigid) – 4ft
3” DuraVent Poly-Pro Flex – 30ft
Poly-Pro elbows – 2 (one at base of chimney and one above boiler)
DuraVent 3PPS-FK Terminal
Intake:
3” PVC – 6ft
3” PVC Sweep 90 – 2 (one above the boiler and one as an intake terminal)
Vent Equivalent length – First elbow is ignored. The terminal is also ignored. From Table 7.14, the equivalent length of 3”
DuraVent Poly-Pro Flex is 2.0ft. From Table 7.1 the equivalent length of the second 90 elbow is 8.7ft. The equivalent length
of the vent system is therefore:
4 + 8.7 + (30 x 2.0) = 72.7ft.
Since Vent Option 34 shows a max vent length of 135ft, the planned vent length of OK.
Intake Equivalent length - First elbow and termination elbow are ignored, leaving just the straight pipe. Equivalent length of
the intake system is therefore 6ft.Since this is less than 135ft, the planned intake length is OK.
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