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Table 10 – Maximum Allowable Exposed Vent Pipe Length (FT / M) With and Without Insulation in Winter Design
WINTER DESIGN
FURNACE SIZE
TEMPERATURE
040
060
080
100
120
* 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.
NOTE: Do not count elbows or pipe sections in terminations or
within furnace (All elbows shown in Fig. 42 and Fig. 43 are not
to be counted).
CAUTION
!
UNIT MAY NOT OPERATE
Failure to follow this caution may result in intermittent
furnace operation.
When installing combustion air and vent system of short pipe
length, the smallest allowable pipe diameter must be used.
NOTE: A 2-in. (51 mm) diameter pipe must be used within
furnace casing. Make all pipe diameter transitions outside furnace
casing per Fig. 39.
3. If required per Table 11, insert perforated disk assembly
(factory-supplied in loose parts bag) in intake housing
where combustion air pipe will be connected. If half disk
set is required, install only shouldered disk half.
Attachment of Combustion Air Pipe
1. Determine location of combustion air intake pipe
connection to combustion air intake housing as shown in
Fig. 37 for application.
2. Reposition combustion air intake housing plug fitting in
appropriate unused intake housing connection.
3. Install pipe grommet (factory-supplied in loose parts bag)
into selected furnace casing combustion-air pipe hole.
Temperature Ambient*
MAX PIPE
DIAMETER
IN (mm)
°F 〈°C)
20 (---7)
1.5 (38)
0 (---18)
1.5 (38)
---20 (---29)
1.5 (38)
20 (---7)
2 (51)
0 (---18)
2 (51)
---20 (---29)
2 (51)
20 (---7)
2 (51)
0 (---18)
2 (51)
---20 (---29)
2 (51)
20 (---7)
2 (51)
0 (---18)
2 (51)
---20 (---29)
2 (51)
20 (---7)
2.5 (64)
0 (---18)
2.5 (64)
---20 (---29)
2.5 (64)
20 (---7)
2.5 (64)
0 (---18)
2.5 (64)
---20 (---29)
2.5 (64)
20 (---7)
3 (76)
0 (---18)
3 (76)
---20 (---29)
3 (76)
20 (---7)
3 (76)
0 (---18)
3 (76)
---20 (---29)
3 (76)
20 (---7)
4 (102)
0 (---18)
4 (102)
---20 (---29)
4 (102)
WITHOUT
INSULATION
FT (M)
51 (16)
28 (9)
16 (5)
45 (14)
22 (7)
10 (3)
65 (20)
35 (11)
20 (6)
55 (17)
48 (15)
30 (9)
70 (21)
47 (14)
28 (9)
40 (12)
40 (12)
38 (12)
70 (21)
50 (15)
28 (9)
70 (21)
61 (19)
37 (11)
70 (21)
48 (15)
23 (7)
4. Insert assembled combustion air inlet pipe into intake
housing as shown in Fig. 37.
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 igniter 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. (3 mm) 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. 40.
NOTE:
(Direct Vent/2-Pipe System ONLY) Moisture in
combustion air intake may be a result of improper termination.
- - 36 - -
WITH 3/8–IN. OR THICKER
INSULATION†
FT (M)
70 (21)
70 (21)
70 (21)
70 (21)
70 (21)
58 (18)
70 (21)
70 (21)
70 (21)
55 (17)
55 (17)
55 (17)
70 (21)
70 (21)
70 (21)
40 (12)
40 (12)
40 (12)
70 (21)
70 (21)
70 (21)
70 (21)
70 (21)
70 (21)
70 (21)
70 (21)
70 (21)
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