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Domestic hot-water heat-up time calculator

Estimate the time and useful heat required to raise a stored water volume between two temperatures.

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All values remain in your browser. Review the assumptions before using the result.

Your result will appear here.Calculate to see the outputs, formula and substituted working.

How the calculation works

Stored-water energy balance with editable fluid properties and efficiency.

Formula

E = m × cp × ΔT; t = E ÷ (P × η)

Worked example

Volume200 L
Temperatures10°C to 60°C
Heater / efficiency12 kW / 90%
Expected heat-up time1.074 h / 64.4 min

Assumptions and limitations

Assumptions

  • The full stored volume is heated uniformly.
  • The entered efficiency applies throughout the heat-up period.

What this does not check

  • Does not include standing losses, draw-off, stratification or heater cycling.
  • Does not size storage or recovery capacity for a demand profile.
Formula version: 1.0 · Last reviewed: 16 August 2026

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Engineering basis: first-principles calculation using user-entered project data. The calculator does not choose design criteria or replace the complete project-specific engineering design.
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