Rinnai RHFE-308 FTR - Manual (Page 17)

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PRE-HEAT
The Pre-heat function will heat a room to the pre-set temperature by the programmed On Time.
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This function operates automatically in conjunction with either of the Timers. When a Timer is selected,
the heater may operate anywhere within an hour prior to the programmed starting time of the Timer.
This function is called Pre-heat due to the way it operates. The room temperature is sensed one hour before
reaching the programmed time of either Timer.
The temperature differential at the time of sensing the room temperature, combined with the data from the
previous operation governs exactly how long before the programmed On time the micro-computer will operate
the heater and ignite the burner.
The following chart may help to improve understanding of the Pre-heat function.
Room temperature sensed
Earlier than usual ignition
Average starting time
Later than average ignition
Programmed time
6:00 6:30 7:00
Warmer than usual
Colder than usual
TIME ELAPSED FROM IGNITION TO PRESET TEMPERATURE Recorded by Micro Computer