HTHOMETALLYTHE PRACTICAL HOME GUIDE

Independent energy/ CALCULATOR

Usable hot-water storage

Estimate the mixed-water volume, shower time and stored heat available from a hot-water tank.

Use the heated water volume available before the draw, not automatically the nameplate volume.
Use a realistic average tank temperature; stratified tanks are not uniform.
Seasonal mains or well-water temperature can change the available mixed volume.
Use the temperature after the mixing valve or at the outlet for this scenario.
Measure with a container and timer when possible.
Use water-running time, not total bathroom occupancy.
Hot water in the delivered mix

67 %

Ideal mixed-water volume

225 L

Equivalent continuous shower time

28.1 min

Equivalent typical showers

3.5 showers

Heat stored above incoming cold water

7.8 kWh

Perfect mixing at constant temperatures, the full stated tank volume initially at one temperature, water at 1 kg/L and 4.186 kJ/(kg·K), and no reheating during the draw. Tank stratification, thermostat deadband, usable outlet position, pipe loss, simultaneous taps, heater recovery, mixing-valve limits and safety requirements are excluded. Actual usable volume can be lower.

FROM ESTIMATE TO ACTION

Use the result, not just the number.

01

Verify the inputs

Measure or document each input. If a value is only an estimate, record its source and test a conservative alternative.

02

Keep the calculation traceable

Save the input link or copied result together with the date, units and assumptions. A number without its inputs cannot be checked later.

03

Confirm the decision

Compare the estimate with the related guide, current product data and requirements that apply at your location before buying or building.

Inputs to verify

Heated tank volume (L)
Use the heated water volume available before the draw, not automatically the nameplate volume.
Average stored hot-water temperature (°C)
Use a realistic average tank temperature; stratified tanks are not uniform.
Incoming cold-water temperature (°C)
Seasonal mains or well-water temperature can change the available mixed volume.
Mixed delivery temperature (°C)
Use the temperature after the mixing valve or at the outlet for this scenario.
Shower flow rate (L/min)
Measure with a container and timer when possible.
Typical shower duration (min)
Use water-running time, not total bathroom occupancy.

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