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Water heating time Calculator
Estimate energy and time needed to raise water temperature. This free water heating time calculator shows the calculation and its assumptions so you can compare your own figures.
Your results
Estimate energy and time needed to raise water temperature.
Calculated outcomes
- Thermal KWh
- 8.721 kWh
- Input KWh
- 9.18 kWh
Assumptions and estimates
- Method: Thermal kWh = litres × 4.186 × positive temperature rise ÷ 3,600. Input divides by efficiency; time = input ÷ power.
- Uses water density of approximately 1 kg/litre and constant heat capacity. Excludes tank standing losses and boiling. It is not a hygiene or scald-safety assessment.
Useful next steps
- Use Compare options to test an alternative side by side.
- Copy, print or download a record of this calculation when you need one.
Reports open your email app addressed to s@s1.ie with the public page address only. Your inputs are never added.
How the water heating time calculation works
Thermal kWh = litres × 4.186 × positive temperature rise ÷ 3,600. Input divides by efficiency; time = input ÷ power.
Uses water density of approximately 1 kg/litre and constant heat capacity. Excludes tank standing losses and boiling. It is not a hygiene or scald-safety assessment.
Using this calculator
- Enter your own figures in the labelled inputs. Keep the currencies, units and time periods consistent.
- Choose any applicable rate profile, pattern or assumption shown for this tool. Open additional inputs when relevant.
- Review heating minutes and heating cost, then read the stated assumptions and eligibility conditions before using the result.
Worked example
This is a static example using illustrative inputs, not facts about you or today’s date. The displayed eligibility selections and assumptions apply only to this example.
See example inputs
- Water volume (litres)
- 150
- Starting temperature (°C)
- 10
- Target temperature (°C)
- 60
- Heater power (kW)
- 3
- Heating efficiency (%)
- 95
- Energy price (€/kWh)
- 0.3
- Heating Minutes
- 183.6 min
- Heating Cost
- €2.75