Bradford White UCG100H199 Installation & Operation Manual page 30

Combustion Air/Gas Ratio Efficiency
This water heater is factory equipped with a gas valve/air mixing venturi system designed and set to maintain
appropriate combustion excess air level (air/gas ratio) under normal operating conditions. The water heater
excess air level is field adjustable in order to optimize water heater efficiency. When the excess air level is
adjusted, an accurate and recently calibrated combustion gas analyzer, which correctly measures carbon
monoxide (CO) and carbon dioxide (CO2) levels in the exhaust gas, as well as an accurate gas pressure
manometer, are mandatory. Carbon dioxide levels in the exhaust gas greater than 11.5% provide high efficiency.
Carbon monoxide (CO) levels increase with increasing carbon dioxide (CO2) levels. Only individuals, installers
or service technicians properly trained, qualified and experienced with adjusting the gas/air mixing venturi
system, and with access to accurate equipment, should attempt to adjust the air/gas ratio. See service manual
for instructions.
DO NOT adjust the air/gas ratio unless you are qualified, experienced and properly trained in the gas valve/air
mixing venturi system air/gas ratio adjustment process and are using accurate, certified CO2, CO and gas
pressure measurement equipment.
If the factory set air/gas ratio is changed, the exhaust gas concentration of CO2 and CO and the gas control
gas pressure must be monitored and properly adjusted no less than every 6 months thereafter.
Temperature Adjustment (24V Control System)
APPROXIMATE TIME/TEMPERATURE RELATIONSHIPS IN SCALDS
Hotter water increases the risk of scald injury. Scalding may occur within five (5) seconds at a temperature

setting of 140F (60 C). To protect against hot water injury, install an ASSE approved mixing valve in the water
system. This valve will reduce point of discharge temperature by mixing cold and hot water in branch water
lines. A licensed plumbing professional or local plumbing authority should be consulted.
This water heater, when set at a lower temperature setting, is not capable of producing hot water of sufficient
temperature for sanitizing purposes.
This water heater is equipped with an energy cut out device to prevent overheating. Should overheating occur
or the gas supply fails to shut off, turn OFF the control panel power switch to the appliance and call a qualified
service agency.
The lower the temperature setting, the greater the energy efficiency, both to heat the water and to maintain the
storage temperature during standby periods. Lower water temperatures also extend tank like. Remember, no
water heating system will provide exact temperatures at all times. Allow for a few days of operation at this
setting to determine the correct temperature setting consistent with the requirements for the installation.
CAUTION
DANGER
Table 6 – Temperature Adjustment
120°F (49°C)
125°F (52°C)
130°F (54°C)
135°F (57°C)
140°F (60°C)
145°F (63°C)
150°F (66°C)
155°F (68°C)
DANGER
CAUTION
NOTICE
More than 5 minutes
1½ to 2 minutes
About 30 seconds
About 10 seconds
Less than 5 seconds
Less than 3 seconds
About 1½ seconds
About 1 second
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