THERM Tankless Water Heater Applications Manual
6 Water Heater Sizing & 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
Major applications (2 GPM or more): Washing machine, bath tub,
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
conjunction with the charts on the next page.
Rule of Thumb Sizing
Number of Major
C 1210 ES/ESC
C 1050 ES
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
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) =
Fill time (sec)
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.
BOSCH THERMOTECHNOLOGY CORPORATION
Number of Minor
Figure 1 Average ground water temperatures
Required 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 330 PN capacity, this application
would require a 520 HN/PN gas tankless water heater.
Data subject to change without notice | 01.2011