37
Table 10 –
Maximum Allowable Exposed Vent Pipe Length ---FT (M)
With and Without Insulation in Winter Design Temperature Ambient*
UNIT SIZE
WINTER DESIGN
TEMPERATURE
°
F (
_
C)
MAX PIPE
DIAMETER ---
IN (mm)
WITHOUT
INSULATION
WITH 3/8–IN. (10 mm) OR
THICKER INSULATION†
060
20 (---7)
2 (51)
44 (13.4)
70 (21.3)
0 (---18)
2 (51)
21 (6.4)
70 (21.3)
---20 (---29)
2 (51)
20 (6.0)
57 (17.3)
080
20 (---7)
2 (51)
55 (16.7)
55 (16.7)
0 (---18)
2 (51)
30 (9.1)
55 (16.7)
---20 (---29)
2 (51)
16 (4.8)
55 (16.7)
20 (---7)
2.5 (64)
58 (17.6)
70 (21.3)
0 (---18)
2.5 (64)
29 (8.8)
70 (21.3)
---20 (---29)
2.5 (64)
14 (4.2)
67 (20.4)
100
20 (---7)
2.5 (64)
40 (12.1)
40 (12.1)
0 (---18)
2.5 (64)
38 (11.5)
40 (12.1)
---20 (---29)
2.5 (64)
21 (6.4)
40 (12.1)
20 (---7)
3 (76)
63 (19.2)
70 (21.3)
0 (---18)
3 (76)
30 (9.1)
70 (21.3)
---20 (---29)
3 (76)
12 (3.6)
70 (21.3)
120
20 (---7)
3 (76)
70 (21.3)
70 (21.3)
0 (---18)
3 (76)
38 (11.5)
70 (21.3)
---20 (---29)
3 (76)
19 (5.7)
70 (21.3)
20 (---7)
4 (102)
65 (19.8)
70 (21.3)
0 (---18)
4 (102)
26 (7.9)
70 (21.3)
---20 (---29)
4 (102)
5 (1.5)
65 (19.8)
* Pipe length (ft / M) specified for maximum pipe lengths located in unconditioned spaces. Pipes located in unconditioned space cannot exceed total allowable
pipe length as specified in Table 11.
† Insulation thickness based on R value of 3.5 per in.
Attachment of Combustion Air Pipe
1. Determine location of combustion air intake pipe
connection to combustion air intake housing as shown in
Fig. 38 for application.
2. Reposition combustion air intake housing plug fitting in
appropriate unused intake housing connection.
3. Install combustion-air pipe grommet (factory-supplied in
loose
parts
bag)
into
selected
furnace
casing
combustion-air pipe hole. (See Fig. 40.)
4. Insert assembled combustion air inlet pipe into intake
housing as shown in Fig. 38.
5. Drill a 1/8-in. (3 mm) hole in 2-in. (51 mm), combustion
air pipe using the hole in intake housing as a guide.
6. Install a field-supplied No. 6 or No. 8 sheet metal screw
into combustion air pipe.
7. Install casing hole filler cap (factory-supplied in loose
parts bag) in unused combustion air pipe casing hole.
NOTE
: Do not attach combustion air intake pipe permanently
to combustion air intake housing since it may be necessary to
remove pipe for service of burner box components or
flame sensor.
Attachment of Combustion Air Intake Housing Plug Fitting
The combustion-air intake plug fitting must be installed in unused
combustion air intake housing. This fitting must be attached by
using RTV sealant, or by drilling a 1/8-in. hole in fitting, using
hole in intake housing as a guide. Install a field-supplied No. 6 or
No. 8 sheet metal screw.
NOTE
: DO NOT OVERTIGHTEN SCREW. Breakage of intake
housing or fitting may cause air leakage to occur.
A plugged drain connection has been provided on this fitting for
use when moisture is found in combustion air intake pipe and
combustion box. If use of this drain connection is desired, drill
out fitting’s tap plug with 3/16-in. (5 mm) drill and connect a
field-supplied 3/8-in. (10 mm) tube. This tube should be routed to
open condensate drain for furnace and A/C (if used), and should
be trapped, as shown in Fig. 42.
NOTE
:
(Direct Vent/2-Pipe System ONLY). Moisture in
combustion air intake may be a result of improper termination.
Ensure combustion air pipe termination is similar to those as
shown in Fig. 44 so that it will not be susceptible to area where
light snow or other sources of moisture could be pulled in.
VENT PIPE
General
Furnace vent connection must be attached as shown in Fig. 38.
CARBON MONOXIDE POISONING AND PROPERTY
DAMAGE HAZARD
Failure to follow this warning could result in property damage,
personal injury, or death.
Vent pipes must be airtight.
!
WARNING
NOTE
: A 2-in. (51 mm) diameter pipe must be used within the
furnace casing. Make all pipe diameter transitions outside furnace
casing per Fig. 41.
The minimum vent pipe length for these furnaces is 5 ft. (1.5 M).
Short pipe lengths (5-8 ft (1.5 -- 2.4 M)) may discharge
condensate droplets. These condensate droplets may be
undesirable. A 12-in. (305 mm) minimum offset pipe section is
recommended to reduce excessive condensate droplets from
exiting vent pipe outlet. (See Fig. 43.)
Attachment of Vent Pipe
1. Determine vent pipe diameter and maximum pipe lengths
using Table 13.
