A.O. Smith BTX-100 Service Handbook page 8

ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
VENTING (CONT)
Pipe Size Requirements
Ensure the correct size pipe has been used for the overall equivalent length of the vent and
intake air piping installed. Longer equivalent lengths require larger pipe sizes, see Table 1.
Maximum Elbow Requirements
Three and four inch vent and intake air pipe installations allow a maximum of 6 - 90° elbows
in the vent pipe AND a maximum 6 - 90°elbows in the intake air pipe. Two inch installations
allow a maximum of 3 - 90° elbows in the vent pipe AND a maximum 3 - 90° elbows the
intake air pipe.
Table 1
NUMBER
90° ELBOWS
1
2
3
4
5
6
Service Notes - Venting
Remove all plastic debris from the edges of intake air pipe sections after cutting on direct
vent installations. Plastic debris left on intake air pipe sections can collect inside and clog the
burner and lead to rough operation and/or ignition failure. See Service Notes page 11.
Using a smaller pipe size than required for a given length or installing more elbows on the
vent pipe can cause the water heater's control system to declare a fault condition, lock out
and display the "Blocked Exhaust" fault message on the UIM display (see page 27).
Overlooking the same requirements for the intake air pipe on direct vent installations or
failing to remove the screen from the intake air connection when direct venting can cause
the water heater's control system to declare a fault condition, lock out and display the
"Blocked Inlet" fault message on the UIM display (see page 27).
Remove This Screen
For Direct Vent
Installations
Technical Literature Department
2" MAXIMUM PIPE
LENGTH FEET (METERS)
20 (6.1)
15 (4.6)
10 (3.0)
4 elbows not allowed in 2" pipe
(use larger pipe size)
5 elbows not allowed in 2" pipe
(use larger pipe size)
6 elbows not allowed in 2" pipe
(use larger pipe size)
Servicing should only be performed by a Qualified Service Agent
3" MAXIMUM PIPE
LENGTH FEET (METERS)
60 (18.3)
55 (16.8)
50 (15.2)
45 (13.7)
40 (12.2)
35 (10.7)
The screen inside the intake air connection is meant to keep
larger debris from entering the blower when the water heater is
installed conventionally; using room air for combustion.
When the water heater is installed in a direct vent configuration
the screen inside the intake air connection on the water heater
must be removed. If left in place it will become clogged over time
and lead to "Blocked Inlet" lock out conditions.
The screen on the intake air termination will keep larger debris
from entering the blower on direct vent installations.
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4" MAXIMUM PIPE
LENGTH FEET (METERS)
120 (36.6)
112 (34.1)
104 (31.7)
96 (29.3)
88 (26.8)
80 (24.3)
Ashland City, TN © 2008