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5
Vertical direct venting
Vent/air termination – vertical
Prepare roof penetrations
1.
Air pipe penetration:
a.
Cut a hole for the air pipe. Size the air pipe hole as
close as desired to the air pipe outside diameter.
2.
Vent pipe penetration:
a.
Cut a hole for the vent pipe. For either combustible
or noncombustible construction, size the vent pipe
hole with at least a 1/2 inch clearance around the
vent pipe outer diameter:
• 4½ inch hole for 3 inch vent pipe
• 5½ inch hole for 4 inch vent pipe
b. Insert a galvanized metal thimble in the vent pipe
hole.
3. Space the air and vent holes to provide the minimum
spacing shown in FIG. 5-1A, page 28.
4. Follow all local codes for isolation of vent pipe when
passing through floors, ceilings, and roofs.
5. Provide flashing and sealing boots sized for the vent pipe
and air pipe.
Termination and fittings
1. Prepare the vent termination coupling and the air
termination elbow (FIG. 5-1A) by inserting bird screens.
Bird screens should be obtained locally.
2. The air piping must terminate in a down-turned 180°
return bend as shown in FIG. 5-1A. Locate the air
inlet pipe no further than 2 feet from the center of the
vent pipe. This placement avoids recirculation of flue
products into the combustion air stream.
3. The vent piping must terminate in an up-turned coupling
as shown in FIG. 5-1A. The top of the coupling must
be at least 1 foot above the air intake. When the vent
termination uses a rain cap as illustrated in FIG. 5-1B
maintain at least 36" (914 mm) above the air inlet. The
air inlet pipe and vent pipe can be located in any desired
position on the roof, but must always be no further than
2 feet apart and with the vent termination at least 1 foot
above the air intake.
4. Maintain the required dimensions of the finished
termination piping as shown in FIG. 5-1A.
5. Do not extend exposed vent pipe outside of building
more than shown in this document. Condensate could
freeze and block vent pipe.
Installation & Operation Manual
(continued)
Multiple vent/air terminations
1. When terminating multiple Knight boilers, terminate
each vent/air connection as described in this manual
(FIG. 5-2).
Terminate all vent pipes at the same height
WARNING
and all air pipes at the same height to
avoid possibility of severe personal injury,
death, or substantial property damage.
2. Place roof penetrations to obtain minimum clearance of
12 inches between edge of air intake elbow and adjacent
vent pipe of another boiler for U.S. installations (see
FIG. 5-2). For Canadian installations, provide clearances
required by CSA B149.1 Installation Code.
3. The air inlet of a Knight boiler is part of a direct vent
connection. It is not classified as a forced air intake with
regard to spacing from adjacent boiler vents.
Figure 5-2 Vertical Terminations with Multiple Boilers
Figure 5-3 Alternate Vertical Terminations with Multiple
Boilers
29
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