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VII. Venting
D. Design Requirements Unique to Split Vent Systems (continued)
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 is 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.
5.
Use of abandoned chimney as vent chase for flexible Stainless Steel venting (option 39) - Vent option 39
permits flexible Stainless Steel venting to be routed to the roof using an abandoned masonry type chimney.
In this application, combustions air is drawn horizontally from a wall terminal. See Figure 7.25a. When using
this option, observe the following requirements:
•
When a masonry chimney containing multiple flues is used as a chase, the flexible stainless vent
installation is permitted through an adjacent UNUSED flue providing local authority having
jurisdiction approves such installation. (Figure 25b)
•
Masonry chimney used as a chase must be structurally sound and in good repair.
•
All venting is stainless steel supplied by the vent manufacturer shown in Table 7.21. The portion of
this venting within the masonry chimney is flexible.
•
When flexible stainless steel is used for combustion product venting, it must be installed at vertical
or near vertical plane. This will insure proper condensate flow back to the boiler. (Figure 7.25a)
WARNING
chimney. A chimney flue is considered UNUSED when it is not being used for any appliance venting. If
chimney is a multiple flue type where one of the multiple flues is being used for an appliance venting, the
flexible polypropylene vent installation is not permitted through any of the adjacent flues.
Asphyxiation Hazard. Flexible stainless steel vent must be installed only in an UNUSED chimney flue. A
chimney flue is considered UNUSED when it is not being used for any appliance venting. If chimney is
a multiple flue type where one of the multiple flues is being used for an appliance venting, the flexible
stainless vent installation is permitted through an adjacent, unused flue providing a local authority having
jurisdiction approves such installation.
107672-03 - 5/18
Asphyxiation Hazard. Flexible polypropylene vent must be installed only in an UNUSED
35
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