Water heating energy calculator
Heating water is the same calculation as any other calorimetry, and water has a stubbornly high specific heat.
kW
%
per kWh
Time to heat
3:29:12
- Energy needed
- 10.460 kWh
- Energy consumed
- 10.460 kWh
- Cost
- 2.929
- Cost of a 50 litre shower
- 0.814
- Energy per litre
- 0.058 11 kWh/L
- Temperature rise
- 50.0 K
Show the working
- Volume of water = 180
- Starting temperature = 10
- Target temperature = 60
- Heater power = 3
- Heating efficiency = 100
- Energy price = 0.28
- Temperature rise = 60 - 10 = 50
- energy_j = 180 * 4184 * 50 = 37 656 000
- Energy needed = 37 656 000 / 3600000 = 10.46
- Energy consumed = 10.46 / (100/100) = 10.46
- Time to heat = 3 > 0 ? 10.46 / 3 * 3600 : 0 = 12 552
- Cost = 10.46 * 0.28 = 2.9288
- Cost of a 50 litre shower = 180 > 0 ? 2.9288 * 50 / 180 : 0 = 0.813 556
- Energy per litre = 180 > 0 ? 10.46 / 180 : 0 = 0.058 111 1
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
Scenarios & local history
Compare a saved scenario
Recent calculations
The formula
- energy = volume x 4184 J per litre per kelvin x temperature rise
Water needs 1.16 Wh to raise one litre by one kelvin. A 180 litre cylinder from 10 to 60 degrees takes about 10.5 kWh.
A heat pump water heater at COP 3 uses a third of the electricity for the same job, which is why the efficiency field goes above 100%.