Independent energy/ CALCULATOR
Estimate the energy, cost and ideal time needed to heat a stored volume between two temperatures.
FROM ESTIMATE TO ACTION
Enter sustained heater input in kW: 3000 W means 3 kW, not 3000. Use power available to water heating in this operating condition, not a whole-building supply rating. This model then applies the entered efficiency; entering useful heat output as input power would apply efficiency a second time. Enter 95 for 95%, not 0.95. The defaults are examples, not verified ratings for your heater.
Use the water volume actually reheated and final minus starting temperature. For 150 L from 10°C to 55°C, the rise is 45°C: about 7.85 kWh of heat and 8.26 kWh input at 95%. With 3 kW input this is 2.75 h, or about 165 min; at a tariff of 0.20 per kWh, energy alone costs about 1.65 in that currency. These temperatures and tariff illustrate arithmetic, not safe settings or a current price.
The example gives about 54.5 L/h for the same 45°C rise, not a measured tap flow or the available mixed shower volume. At unchanged volume, rise and efficiency, doubling input power halves ideal time but leaves input kWh and energy cost unchanged. The model has no draw-off during recovery, tank stratification, thermostat cycling or separately added standby losses. Use product recovery data and actual operating limits for selection; ideal time is not a guaranteed completion time.