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Page 5
Table 3. Maximum Combined Length of Combustion Air and Vent Piping in Feet.
Table 3 specifies 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 5). The vent pipe is 42
feet long and has five elbows. Per Table 3, 5"
piping must be used. (Only 16 feet of 4" vent pipe
would be allowable.)
2. A Model 220 heater is to be installed in a two-
pipe system (see Figure 6). 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-3d.Combustion Air and Vent Pipe
Installation
The Hi-E
2 must be vented to the outdoors. It must
not be vented in common with any other appliance,
even if that appliance is of the condensing type.
Common venting can result in severe corrosion of the
Hi-E
2 or of the other appliances or their venting, or
escape of combustion product gases through such
appliances or vents. Do not vent the Hi-E
2 to a
fireplace chimney or building chase.
Combustion air ducting, when provided, must not
be shared with any other appliance or with another Hi-
E
2. Doing so may result in flow of air through the
other appliances instead of directly from the outdoors.
The combustion air intake and vent outlet must
be located exterior to the building and in the same
pressure zone - i.e. both through the roof or both
through a side wall. The vent terminal must be located
in accordance with local codes, as applicable, and in
accordance with the following:
1. Locate the vent terminal so that it will not be
damaged by pedestrians and other traffic, and so
that the discharge is not offensive. The National
Fuel Gas Code requires a through-wall vent
terminal be at least 7 feet (2.13 m) above grade if
located at a public walkway.
Figure 5. “One-pipe” installation.
4'
8'
18'
10'
2'
Total Length: 42'
Total Elbows: 5
Figure 6. “Two-pipe” installation.
EHE350
4'
7'
4'
5'
2'
Combustion
Air Pipe
Vent
Pipe
EHE220
Comb.
Air Vent Total
Length 13' 9' 22'
Elbows 3 1 4
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 flow
to or from the heater. Also, a large heater requires
larger pipe than a small heater because it operates with
higher flow of combustion air and exhaust products.
Model
Pipe Size
Inches (cm)
Number of Elbows
1 2 3 4 5 6 7 8 9 10
Total Len
g
th 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)