A.O. Smith CYCLONE Xi BTH 500A Owner's Manual page 33

TWO TEMPERATURE - TWO HEATERS (ONE PRE-HEATER/ONE BOOSTER HEATER)
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE TEMPERATURE
AT FIXTURES. SEE WATER TEMPERATURE CONTROL WARNING ON
PAGE 3. IF HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO
OBTAIN ADEQUATE BOOSTER OUTPUT, ADD AN ANTI-SCALD VALVE
FOR HOT WATER SUPPLIED TO FIXTURES
WITH OR WITHOUT BUILDING RECIRCULATION
DANGER
* PIPE RELIEF VALVE TO OPEN DRAIN
** 140°F (60°C)TO 150°F (66°C) SHOULD BE MAXIMUM WATER
TEMPERATURE MAINTAINED IN THE PRE-HEATERS.
120°F (49°C) SHOULD BE THE MINIMUM TEMPERATURE OF
WATER IN THE PRE-HEATERS.
CONNECT CIRCULATING LINE FROM FIXTURES, IF USED,
TO COLD WATER SUPPLY LINE OF PRE-HEATER.
CONNECT CIRCULATING LINE OF 180°F (82°C) OR BOOSTED
WATER, IF USED, TO INLET WATER LINE TO BOOSTER.
INSTALL IN ACCORDANCE WITH LOCAL CODES.
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