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5
HIGH ALTITUDE INSTALLATIONS
WARNING
INSTALLATIONS ABOVE 2000 FEET (610 METERS) REQUIRE
REPLACEMENT OF THE BURNER ORIFICE IN ACCORDANCE
WITH SECTION 8.1.2 OF THE NATIONAL FUEL GAS CODE (ANSI
Z223.1). FAILURE TO REPLACE THE ORIFICE WILL RESULT
IN IMPROPER AND INEFFICIENT OPERATION OF THE
APPLIANCE RESULTING IN THE PRODUCTION OF
INCREASED LEVELS OF CARBON MONOXIDE GAS IN EXCESS
OF SAFE LIMITS WHICH COULD RESULT IN SERIOUS
PERSONAL INJURY OR DEATH.
You should contact your gas supplier for any specific changes
which may be required in your area.
As elevation above sea level is increased, there is less oxygen
per cubic foot of air. Therefore, the heater input rate should be
reduced at high altitudes for satisfactory operation with the
reduced oxygen supply. Failure to make this reduction would
result in an overfiring of the heater causing sooting, poor
combustion and/or unsatisfactory heater performance.
REQUIREMENTS
Ratings specified by manufacturers for most appliances apply
for elevations up to 2000 feet. For elevations above 2000 feet,
ratings must be reduced at the rate of 4% for each 1000 feet
above sea level. For example, if a heater is rated at 120,000
Btuh at sea level, to rate the heater at 4000 feet, you subtract 4
(once for each thousand feet) x.04 (4% input reduction) x 120,000
Btuh (original rating) from the original rating. Therefore, to
calculate the input rating at 4,000 feet: 4 x .04 x 120,000 =19,200
Btuh, 120,000 - 19,200 = 100,800 Btuh. At 6000 feet the correct
input rating should be 91,200 Btuh.
The input reduction is primarily achieved by reducing the size of
the main burner orifices. To do this, the main burner orifices
require replacement with orifices sized for the particular
installation elevation. Correct orifice sizing and parts may be
obtained from A.O. Smith Water Products Company. When
ordering, be sure to state the model number and the altitude of
the location where the water heater is being installed.
Upon completion of derating of the heater, adjustment to the gas
pressure regulator may be required. See CHECKING THE
INPUT section in this manual for inlet and manifold pressure
requirements.
Also due to the input rating reduction required at high altitudes,
the output rating of the appliance is also reduced and should be
compensated for in the sizing of the equipment for application.
FEATURES
HIGH LIMIT SWITCH
The digital thermostat (Fig. 2) contains the high limit (energy
cutoff) sensor. The high limit switch interrupts main burner gas
flow should the water temperature reach 203°F (95°C).
In the event of high limit switch operation, the appliance cannot
be restarted unless the water temperature is reduced to
approximately 120°F (49°C). The high limit reset button on the
front of the control then needs to be depressed.
Continued manual resetting of high limit control, preceded by
higher than usual water temperature is evidence of high limit
switch operation. The following is a possible reason for high
limit switch operation:
• A malfunction in the thermostatic controls would allow the
gas valve to remain open causing water temperature to exceed
the thermostat setting. The water temperature would continue
to rise until high limit switch operation.
Contact your dealer or service agent if continued high limit switch
operation occurs.
DIGITAL THERMOSTAT
FIGURE 2
ELECTRONIC IGNITION CONTROL
Each heater is equipped with a ignition module. The solid sate
ignition control (Fig. 3), ignites the main burner by utilizing a
silicone nitride ignitor. The silicone nitride ignitor shuts off during
the heating cycle and the main burner flame is sensed through
a remote flame sensor integral to the silicone nitride ignitor
assembly. The ignition control will try to ignite the main burner
three times before lockout. Then it waits one hour before trying
again to ignite the main burners. This is a continuous cycle.
IGNITION CONTROL BOARD
FIGURE 3
EXHAUST INDUCER (BLOWER ASSY.)
All BTN 120-400 models are equipped with an exhaust inducer.
The inducer assists in drawing in fresh air to the unit for
combustion and then assists in dispensing the combustion by-
products into the venting leading outside.