A. O. Smith Water Products Company
Service Handbook
Irving, Texas 2000©
Training Department
12
VENTING
Equivalent Feet of Pipe Intake or Exhaust
MANIFOLD GAS
SUPPLY GAS
Gas Type
Minimum
Inches
W.C.
Maximum
Inches
W.C.
Natural
5
10.5
Propane
11
13.8
NOTE: Pressure without capacity will result in
lockout. Follow the piping guidelines in the
instruction manual.
The supply gas pressure in normally measured
at the dirt leg or at the inlet gas pressure tapping
on the gas valve. This reading must be measured
with 'flowing' gas.
Regulated Gas Supply
Line
Main Gas Shutoff Valve
Dirt Leg Tee
The manifold gas pressure is measured at the
manifold pressure tap of the gas valve when the
gas is flowing.
The gas valves used on all BTH water heaters are
24 volt AC combination step opening gas valves.
They incorporate the main valve, and gas pressure
regulators into one body.
Pipe Cap
Pressure Regulator Adjustment
(Cover Screw)
Inlet Pressure Tap
Gas Inlet
Gas Valve On/Off
TH & TR Terminals
(Main Valve)
Manifold
Pressure Tap
Gas Outlet
Gas Type
Minimum/Maximum
Inches W.C.150/199
Minimum/Maximum
Inches W.C. 120/250
Natural
3.5
4.0
Propane
10
10.0
Number of
90° Elbows
3" Minimum
Pipe (Feet)
3"
Maximum
Pipe (Feet)
4"
Maximum
Pipe
(Feet)
One (1)
7
45
115
Two (2)
7
40
110
Three (3)
7
35
105
Four (4)
7
30
100
Five (5)
7
95
Six (6)
7
90
VENT LENGTH TABLE
4-inch PVC may be used for a MAXIMUM intake of ONE HUNDRED TWENTY (120) EQUIVALENT FEET
and a MAXIMUM exhaust of ONE HUNDRED TWENTY (120) EQUIVALENT FEET. The maximum number
of 90° elbows with the 4-inch venting is six (6) on the intake and six (6) on the exhaust. A 90° elbow is equal
to five (5) equivalent feet of pipe. One (1) 90° elbow is equal to two (2) 45° elbows. Any venting configuration
using less than 50 equivalent feet should use 3-inch venting. See Vent Length Table.
The 3-inch venting terminals (provided) must be used with the 4-inch venting by adding 4 x 3 reducing
couplings at the venting terminals. A reducing coupling is also needed immediately after the condensate
elbow (exhaust) and immediately before the 3-inch blower adapter (intake) if direct venting is installed. See
Vent Length Table.
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Summary of Contents for BTH 120
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