Burnham K2WTC - Page 31

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VII. Venting C. Design Requirements Unique to Vertical Venting Systems (continued)
Terminal Option J: DiversiTech Concentric Terminal (Acceptable for Vent Option 5) - This terminal is shown in Figure
7.16 and may be used with CPVC/PVC vent systems. See Section VII - E of this manual and the DiversiTech instructions
provided with the terminal, for installation details.
Terminal Option K: DuraVent PolyPro Concentric Terminal (Acceptable for Vent Option 6) - This terminal is shown in
Figure7.18andmaybeusedwithDuraVent3”PolyProventsystems.UseacompatibleDuraVentroofashingandstorm
collar in accordance with the DuraVent instructions for this terminal See Section VII - F of this manual and the DuraVent
instructions provided with the terminal, for installation details.
2. Vertical Vent and Air Intake Location – Observe the following clearances from roof mounted terminals:
• Bottom of air intake opening must be at least 12” above the normal snow line anticipated on the roof.
• Exhaust opening must be at least 2ft above any portion of the roof or structure located within horizontally within 10ft.
• For terminal option H, maintain at least 12” of vertical separation between the exhaust and intake opening as shown in
Figure 7.15 and 7.17.
3. Requirements for B-Vent Air Chase Options – Observe the following additional requirements when using an abandoned
B-vent chimney as an air chase as described in Options # 9 & 10. Also refer to Figures 7.19 & 7.20.
• B vent must be clean and in good condition.
 • UseofexPolypropyleneoutsideofB-ventchimneyisnotpermitted.
• All joints and seams in the B-vent must be sealed with RTV. If these seams are not accessible, vent options 9 - 10 cannot
be used while complying with the National Fuel Gas Code (as an alternative, the B-vent chimney can be used as a chase
for the vent pipe while combustion air is piped from an outside wall - see Section VII - D for additional details).
• All venting is Polypropylene supplied by the vent manufacturer shown in Table 7.13b. The portion of this venting within
  theB–ventisexible.
 • Allexpipemustbeinstalledvertically.Uptotwooffsets(fourbends)maybemadeintheverticalrunofexpipe.
Bends used to make these offsets may not exceed 45 degrees.
 • Becausetheexpipeiscorrugated,ithasahigherpressuredropthantherigidpipeusedelsewhereintheventsystem.
  EquivalentlengthsforexventingareshowninTable7.14.ReducethemaximumallowableventlengthshowninTable
  7.13bbythisequivalentlengthforeachfootofexpipeused,aswellasforeachelbowinadditiontotherst.The 
termination is not counted. If offsets (described above) are present, the equivalent length of the bends in these offsets
can also be ignored.
Example: A 135MBH model is to be installed as using Vent Option 9 as shown in Figure 7.19. The following components
are used:
Vent:
3” DuraVent Poly-Pro (Rigid) – 4ft
3” DuraVent Poly-Pro Flex – 20ft
Poly-Pro elbows – 2
DuraVent 3PPS-VFT Terminal (exhaust side)
Intake:
3” PVC – 6ft
3” PVC Sweep 90 – 3
Turn in B vent Tee
Straight B-vent (6” or larger) containing ex vent – 20ft
DuraVent 3PPS-VFT Terminal (intake side)
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 + (20 x 2.0) = 52.7ft.
Since Vent Option 9 shows a max vent length of 135ft, the planned vent length of OK.
Intake Equivalent length - First elbow and the turn in the B vent tee are ignored, leaving two sweep 90 elbows that must be
counted. From Table 7.1, the equivalent length of each of these elbows is 4.0ft. From Table 7.14 the equivalent length of the
B vent containing ex is 1.0ft. Equivalent length of the intake system is therefore:
(2 x 4.0) +6 +(20 x 1.0) = 34.0ft.
Since this is less than 135ft, the planned intake length is OK.