Hi-E2
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2. A Model 220 heater is to be installed in a two-
pipe system (see Figure 7). The combustion
air pipe is to be 13 feet long with three elbows
and the vent pipe is to be 9 feet long with one
elbow. Since the total is 22 feet and four elbows,
4" pipe must be used. (Table 3 indicates that
the maximum length of 3" pipe is 11 feet for a
system with four elbows.)
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.
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.)
Figure 5. Connection of combustion air pipe to heater.
Table 3. Maximum Combined Length of Combustion Air and Vent Piping in Feet.
Figure 6. “One-pipe” installation.
Figure 7. “Two-pipe” installation.
4'
7'
4'
5'
2'
Combustion
Air Pipe
Vent
Pipe
EHE220
Comb.
Air Vent Total
Length 13' 9' 22'
Elbows 3 1 4
Model Pipe Size
Inches
(cm)
Number of Elbows
123456789
10
Total Length of Pipe - Feet (m)
220 3” 35 (10.6) 27 (8.2) 19 (5.8) 11 (3.4) NA NA NA NA NA
NA
4” 173 (52.7) 163 (49.6) 153 (46.6) 143 (43.5) 132 (40.2) 122 (37.1) 112 (34.1) 102 (31) 92 (28) 81 (24.6)
350 4” 61 (18.6) 50 (15.2) 39 (11.9) 27 (8.2) 16 (4.8) NA NA NA NA NA
5” 225 (68.6) 211 (64.3) 197 (60) 184 (56) 170 (51.8) 157 (47.8) 143 (43.5) 130 (39.6) 116 (35.4) 103 (31.4)
4'
8'
18'
10'
Total Length: 42'
Total Elbows: 5
EHE350
2'
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