Understanding the Relationship Between Power and Hot Water Output
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3.5kW–5.5kW: Suitable for washbasins and kitchen sinks
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7kW–9kW: Ideal for one shower + kitchen/washbasin use
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11kW–15kW: For 1–2 people, shower + kitchen + washing machine
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18kW–24kW and more: For larger families, multiple taps simultaneously (e.g., two showers in parallel)
Choosing the Right Power Output According to Household Size
| Household Size | Recommended Power Output | Typical Usage Scenarios |
| Single person/Couple | 3.5kW-7kW | Washbasin, kitchen |
| Family of 3 people | 9kW-11kW | Shower + kitchen + washing machine |
| Family of 4 people | 12kW-15kW | Two taps simultaneously possible |
| 5 people or more | 18kW-24kW | Multiple showers + kitchen + bathtub simultaneously |
Note: These recommendations are a rough guide – factors such as water pipe pressure and regional incoming water temperature (especially in winter) should also be considered.
Consider Frequency and Behavior of Use
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Multiple water taps simultaneously? → e.g., two showers: at least 15 kW
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Only short use in the morning and evening? → 9 kW–11 kW sufficient
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With a bathtub? → at least 18 kW to fill a tub faster
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Only for kitchen or guest toilet? → 3.5 kW–5.5 kW is enough
Product Examples
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ThermoMate 3.5 kW Small Tankless Water Heater: Compact design, water temperature adjustable between 30 °C and 45 °C. The touch control panel with digital display allows precise temperature control. Integrated protection against overheating, dry running, and leakage current offers maximum safety – ideal for kitchen or washbasin.
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ThermoMate 18 kW Tankless Water Heater: With a modern LED display and touch control panel, the water temperature can be continuously adjusted between 30 °C and 60 °C. Integrated safety features such as overheating protection, dry run protection, and automatic shutdown ensure maximum safety in everyday life.
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ThermoMate 21 kW High-Performance Tankless Water Heater: Ideal for bathtubs, multiple showers, and households with high hot water demand. Equipped with dry run protection, overheating protection, and automatic shutdown function – for safe and reliable use in family households.
Conclusion
Choosing the right power output for an electric tankless water heater does not follow the motto "the more, the better." Rather, the following points should be carefully considered:
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Number of people living in the household
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Hot water consumption habits (e.g., simultaneous use)
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Space and installation location
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Winter temperatures in your region (northern countries usually require higher power)