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Applications manual
Application manual | 11.2007
Bosch Water Heating
2.1 Sizing tankless water heaters
Defi nitions
Major applications (2 GPM or more): Washing machine, bath tub,
shower nozzle
Minor applications(1.5 GPM or less): Low fl ow shower head,
bathroom sink, kitchen sink
Rule of thumb sizing
The tables below provide a general rule of thumb when sizing for
most residential applications. For commercial applications or for a
more detailed sizing method, use the instructions below in conjunc-
tion with the charts on the next page.
Sizing by Chart
Measure the fl ow rates at each fi xture that will be used simultane-
ously and add them together. If only one application will be used
at a time measure each fi xture and use the maximum fl ow rate
observed.
Rule of Thumb Sizing
Model Number Number of Major
Applications
Number of Minor
Applications
GWH 715 ES 2 0
GWH C 800 ES 2 1
GWH 425 HN/PN/EF 1 1
GWH 425 HN/PN/EF 0 2
GWH 260 PN 1 0
RP17PT 1 0
RP27PT 1 1
Using a known volume container, record several fi ll times. Per-
form the calculation below to determine the fl ow rate (a one
gallon fi ll time of 30 seconds is 2.0 gallons per minute (GPM):
Flow rate (GPM) =
Volume (gallons)
Fill time (sec)
sec
min
60
x
Using a thermometer, measure the incoming water temperature.
Subtract this temperature from the desired hot water temperature
to get the degree rise. So, if the desired hot water temperature is
120F and incoming temperature is 55F, the desired degree rise is
65F.
This example requires a fl ow rate of 2.0 GPM at a 65˚F rise. The
data point is shown on each graph. Since the demand is above
the GWH 260 PN capacity, this application would require a GWH
425 HN/PN/EF gas tankless water heater. The electrical model
used for this application would be the RP27PT electric tankless
water heater.