4 | Applications manual |
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2.1 Sizing tankless water heaters
Definitions
Major applications (2 GPM or more): Washing machine, bath tub, shower nozzle
Minor applications(1.5 GPM or less): Low flow 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 flow rates at each fixture that will be used simultane- ously and add them together. If only one application will be used at a time measure each fixture and use the maximum flow rate observed.
Rule of Thumb Sizing
Model Number | Number of Major | Number of Minor |
| Applications | Applications |
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GWH 715 ES | 2 | 0 |
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GWH C 800 ES | 2 | 1 |
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GWH 425 HN/PN/EF | 1 | 1 |
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GWH 425 HN/PN/EF | 0 | 2 |
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GWH 260 PN | 1 | 0 |
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RP17PT | 1 | 0 |
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RP27PT | 1 | 1 |
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Using a known volume container, record several fill times. Per- form the calculation below to determine the flow rate (a one gallon fill time of 30 seconds is 2.0 gallons per minute (GPM):
Flow rate (GPM) = | Volume (gallons) | x 60 | sec | |
Fill time (sec) | min | |||
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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 flow 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.
Application manual 11.2007 | Bosch Water Heating |
