-- 35 --
Table 10 – Maximum Allowable Exposed Vent Pipe Length -- Ft. (M) With and Without Insulation
in Winter Design Temperature Ambient*
FURNACE SIZE
WINTER DESIGN
TEMPERATURE
°
F
〈°
C)
MAX PIPE
DIAMETER
IN (mm)
WITHOUT
INSULATION
FT (M)
WITH 3/8–IN. (10 mm) OR
THICKER INSULATION†
FT (M)
040
20 (---7)
1.5 (38)
51 (16)
70 (21)
0 (---18)
1.5 (38)
28 (9)
70 (21)
---20 (---29)
1.5 (38)
16 (5)
70 (21)
20 (---7)
2 (51)
45 (14)
70 (21)
0 (---18)
2 (51)
22 (7)
70 (21)
---20 (---29)
2 (51)
10 (3)
58 (18)
060
20 (---7)
2 (51)
65 (20)
70 (21)
0 (---18)
2 (51)
35 (11)
70 (21)
---20 (---29)
2 (51)
20 (6)
70 (21)
080
20 (---7)
2 (51)
55 (17)
55 (17)
0 (---18)
2 (51)
48 (15)
55 (17)
---20 (---29)
2 (51)
30 (9)
55 (17)
20 (---7)
2.5 (64)
70 (21)
70 (21)
0 (---18)
2.5 (64)
47 (14)
70 (21)
---20 (---29)
2.5 (64)
28 (9)
70 (21)
100
20 (---7)
2.5 (64)
40 (12)
40 (12)
0 (---18)
2.5 (64)
40 (12)
40 (12)
---20 (---29)
2.5 (64)
38 (12)
40 (12)
20 (---7)
3 (76)
70 (21)
70 (21)
0 (---18)
3 (76)
50 (15)
70 (21)
---20 (---29)
3 (76)
28 (9)
70 (21)
120
20 (---7)
3 (76)
70 (21)
70 (21)
0 (---18)
3 (76)
61 (19)
70 (21)
---20 (---29)
3 (76)
37 (11)
70 (21)
20 (---7)
4 (102)
70 (21)
70 (21)
0 (---18)
4 (102)
48 (15)
70 (21)
---20 (---29)
4 (102)
23 (7)
70 (21)
140
20 (---7)
3 (76)
60 (18)
60 (18)
0 (---18)
3 (76)
60 (18)
60 (18)
---20 (---29)
3 (76)
44 (13)
60 (18)
20 (---7)
4 (102)
70 (21)
70 (21)
0 (---18)
4 (102)
57 (17)
70 (21)
---20 (---29)
4 (102)
30 (9)
70 (21)
* Pipe length (ft) specified for maximum pipe lengths located in unconditioned spaces. Pipes located in unconditioned space cannot exceed total allowable pipe
length as specified in Table 10.
† Insulation thickness based on R value of 3.5 per in.
COMBUSTION AIR PIPE
General
Furnace combustion-air connection must be attached as shown in
Fig. 35. Combustion-air intake housing plug may need to be
relocated in some applications.
For Non-Direct Vent (1-Pipe) system, combustion-air must
terminate outside of furnace casing with 1 elbow. Orient elbow so
that its opening faces down for upflow or downflow applications.
Orient elbow so that its opening faces sideways (left or right) for
horizontal left or horizontal right applications (See Fig. 35.)
Maintain a 3-in minimum clearance between the opening of the
combustion-air inlet pipe and any object.
UNIT CORROSION HAZARD
Excessive exposure to contaminated combustion air may
result in safety and performance related problems.
Combustion air must not be taken from inside structure
because inside air is frequently contaminated by halogens,
which include fluorides, chlorides, bromides, and iodides.
These elements are found in aerosols, detergents, bleaches,
cleaning solvents, salts, air fresheners, adhesives, paint, and
other household products. Locate combustion-air inlet as far
as possible from swimming pool and swimming pool
pump house.
pipe. Pick the larger of these 2 pipe diameters and use this
diameter for both combustion-air and vent pipes.
CAUTION
!
NOTE
: All pipe joints must be cemented except attachment of
the combustion-air pipe to the inlet housing connection, since it
may be necessary to remove the pipe for servicing.
58MCB