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Hi-E2
Figure 5. Connection of combustion air pipe to heater.
2G-3b. Piping Materials
Vent piping must be corrosion resistant because
combustion condensate is usually present on its
internal surfaces. Only the following materials are
acceptable for vent piping:
PVC
Class 100, Class 125 or Schedule 40
CPVC
Schedule 40
®
29-4C
Stainless steel venting materials listed for
venting of condensing gas-fi red appliances.
29-4C
®
is a trademark of Allegheny Teledyne.
Combustion air piping may be single-wall
galvanized steel pipe or any of the above materials.
2G-3c. Size and Length of Combustion
Air and Vent Piping
Piping for combustion air and venting must
be large enough to avoid restriction of the heater
combustion system. Pipe diameter, number of elbows
and length of pipe determine how much it restricts
fl ow to or from the heater. Also, a large heater requires
larger pipe than a small heater because it operates with
higher fl ow of combustion air and exhaust products.
Table 3 specifi es the allowable length of piping for
various situations.
Model
Pipe Size
Inches
1
(cm)
350
4"
61 (18.6)
5"
225 (68.6)
Table 3. Maximum Combined Length of Combustion Air and Vent Piping in Feet.
2
3
4
Total Length of Pipe - Feet (m)
50 (15.2)
39 (11.9)
27 (8.2)
211 (64.3)
197 (60)
184 (56)
Total Length: 42'
Total Elbows: 5
EHE350
Figure 6. "One-pipe" installation.
4'
Combustion
Air Pipe
7'
Comb.
Air Vent Total
Length 13'
9'
22'
Elbows 3
1
4
Figure 7. "Two-pipe" installation.
The following examples illustrate use of table 3:
1.
A Model 350 heater is to be installed in a one-
pipe system (see Figure 6). The vent pipe is 42
feet long and has fi ve elbows. Per Table 3, 5"
piping must be used. (Only 16 feet of 4" vent
pipe would be allowable.)
Number of Elbows
5
6
7
16 (4.8)
NA
NA
170 (51.8)
157 (47.8)
143 (43.5)
Page 5
4'
8'
18'
10'
2'
Vent
Pipe
4'
5'
2'
8
9
10
NA
NA
NA
130 (39.6)
116 (35.4)
103 (31.4)
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