Water Heater Recovery Time & Energy Calculator (Liters, Watts & ΔT)

Calculate how long an electric water heater or DHW tank takes to heat water based on tank volume in liters, heating element wattage and temperature rise.

Tank Volume (Liters)

Heating Element Power (W)

Cold Water Inlet Temp (°C)

Target Hot Water Temp (°C)

Heating Recovery Time3 h 02 min

Total Energy Required4.56 kWh

Temperature Rise (ΔT)48 °C

Usable Water Mixed at 38°C147 Liters

Thermodynamic Formula for Water Heating Recovery Time

Thermodynamic Constant: The specific heat capacity of water is 4,186 J/(kg·K), equal to 1.163 Wh per liter per °C of temperature increase.

Required Energy (kWh) = (Liters × 1.163 × (T_target - T_inlet)) / (1000 × η)
Recovery Time (Hours) = (Energy in kWh × 1000) / Power (Watts)

Standard Heating Times for Commercial Electric Water Heaters (ΔT = 45°C)

Tank Volume	Users (Showers/day)	Typical Power	Time (15°C to 60°C)	Energy per Cycle
50 Liters	1 - 2 people	1.500 W	1 h 47 min	2,67 kWh
80 Liters	2 - 3 people	1.500 W	2 h 51 min	4,27 kWh
100 Liters	3 - 4 people	2.000 W	2 h 40 min	5,34 kWh
150 Liters	4 - 5 people	2.400 W	3 h 20 min	8,01 kWh

Frequently Asked Technical Questions (FAQ)

How do you calculate electric water heater recovery time?

Multiply tank volume (Liters) by 1.163 Wh/(L·°C) and by the temperature rise ΔT (°C), then divide by element wattage (W).

Why store domestic hot water at 60°C?

Storing water at 60°C prevents Legionella bacteria growth and nearly doubles the usable mixed shower water volume at 38°C.