Bosch GWH C 920 ES - 6 Bosch Water Heating Models & Specifi Cations; Sizing Tankless Water Heaters

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Bosch applications manual
Bosch applications manual | 06.2009
BOSCH THERMOTECHNOLOGY CORPORATION
6 Bosch Water Heating Models and
Specifi cations
This section describes the water heaters available from Bosch
Thermotechnology Corporation and provides a general overview to
the specifi cations of that particular model. More detailed
information is contained in the installation manuals. Download
these manuals at www.BoschPro.com.
6.1 Sizing tankless water heaters
Defi nitions
 Major applications (2 GPM or more): Washing machine, bath tub,
shower nozzle
 Minor applications(2 GPM or less): Low fl ow shower head, bath-
room 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 Sizing by Chart instructions
below in conjunction with the charts on the next page.
Rule of Thumb Sizing
Model Number Number of Major
Applications
Number of Minor
Applications
GWH C 920 ES/ESC 3 1
GWH 715 ES 2 0
GWH C 800 ES 2 1
GWH 425 HN/PN 1 1
GWH 425 HN/PN 0 2
GWH 260 PN 1 0
RP17PT 1 0
RP27PT 1 1
Sizing by Chart
 Measure the fl ow rates at each fi xture that will be used
simultaneously 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
.
 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.
For reference, see average ground water temperature map. Sub-
tract this temperature from the desired hot water temperature to
get the degree rise. If the desired hot water temperature is 120F
and incoming temperature is 55F, the desired degree rise is 65F.
Figure 1 Average ground water temperatures
 This example requires a fl ow rate of 2.0 GPM at a 65˚F rise. Refer
to the graphs on the following page. Since the demand is above
the GWH 260 PN capacity, this application would require a GWH
425 HN/PN gas tankless water heater. The electrical model used
for this application would be the RP27PT electric tankless water
heater.