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935SB: Installation, Start-up, Operating and Service Maintenance Instructions
Non-Direct Vent / 1-Pipe System
The vent pipe for a Non Direct Vent (1-pipe) system must terminate
outdoors. References to vent clearances required by National Code
authorities (see
Fig.
47). Allowable vent terminations (see
A combustion air inlet pipe to the outdoors is not required for a
Non-Direct (single-pipe) Vent System. A 12-in. long section of pipe with
a tight radius 2-in. (51 mm) 90 degree elbow is required to be attached to
the furnace. (see
Fig.
48) This short inlet air pipe helps to ensure stable
combustion, as well as allow for sound attenuation. To aid sound
attenuation, point the inlet air pipe away from occupants. An extra elbow
and/or five feet of pipe may be used to accomplish the sound attenuation
function.
Ventilated Combustion
Air intake pipe
Pipe hangar
Ventilated Combustion Air
intake termination in crawl
space
Fig. 49 – Vent Terminations for Ventilated Combustion Air
Size the Vent and Combustion Air Pipes
General
Furnace combustion air and vent pipe connections are sized for 2-in. (50
mm ND) PVC/ABS DWV pipe. The combustion air and vent pipe
connections also accommodate 60 mm polypropylene venting systems
with outside diameters of approximately 60 mm (2-3/8 inches). Any pipe
diameter change should be made outside furnace casing in vertical pipe.
Any change in diameter to the pipe must be made as close to the furnace
as reasonably possible (see
Fig.
The Maximum Vent Length for the vent and combustion air pipe (when
used) is determined from the Maximum Equivalent Vent Length
(Table
16) minus the number of fittings multiplied by the deduction for
each type of fitting used
(Table
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
Fig.
3" (76 mm)
12" (305 mm)
CRAWL SPACE
highest level of insulation
ATTIC
51).
17).
OPTIONAL CONFIGURATION FOR COMBUSTION
44).
AIR INLET PIPE
In applications where there is a risk of excessive moisture entering the
combustion air inlet pipe, a moisture trap may be added to the inlet pipe
to help prevent moisture from entering the furnace from the combustion
air inlet pipe. (see
When sizing venting systems, the equivalent length of the optional
moisture trap (15 feet/5 M) must be taken into account.
Representative drawing only, some models may vary.
Fig. 50 – Sample Inlet Air Pipe Connection for Polypropylene
NOT IN
HORIZONTAL
SECTION
A10497
Fig. 51 – Combustion Air and Vent Pipe Diameter Transition
Recommended Combustion Air Inlet Moisture Trap
Recommended to prevent moisture from trickling into the furnace
vestibule, a trap can be installed in the intake air pipe near the furnace.
To prevent moisture, connecting a drain line to the trap is recommended
as trace amounts of moisture will evaporate into the intake air stream. If
the combustion air inlet is located near a moisture exhaust duct, or there
are other concerns of excessive moisture being drawn into the
combustion air inlet, it is encouraged to connect a drain line to the trap.
The trap can be constructed from a running tee of the same diameter of
the intake air pipe with EITHER a removable cap attached to a 6-inch
long pipe connected to the tee or the External Vent Trap Kit to help
prevent contaminants from entering the furnace (see
The External Vent Trap Kit accessory may be used as a trap for the
combustion air inlet pipe if a large amount of moisture must be removed.
The drain line may be connected to the same drain as the furnace
condensate and the evaporator coil condensate line ONLY if the inlet air
trap drain and the evaporator coil drain empty into an open segment of
pipe above the drain. The drain line must be connected downstream of
the condensate trap float switch (see
Vent Trap Kit, refer to those instructions for proper drain connections.
35
NOTICE
!
Fig.
52).
Venting Systems
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
Location and Elbow Configuration
Fig.
11). When using the External
A12220
A93034
Fig.
52).
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