Water Heating Time Calculator (Boiler, Kettle, Tank)
How long an electric water heater, kettle or immersion heater takes to bring water to temperature, the energy it uses and what it costs.
Results
Heating time
165.2
min
Heating time in hours
2.75
h
Heat put into the water
5.233
kWh
Cost of the energy used
1.10
The dashed line marks the value you entered.
What this tool does
Heating a litre of water by one degree takes 4.186 kJ, so a 100-litre tank going from 15 to 60 °C needs about 5.2 kWh — at 2 kW that is close to three hours. A 1.5-litre kettle at 2.2 kW boils in about four minutes for the same reason. Efficiency covers heat lost while heating; it does not include the standing losses of a tank kept hot all day, which can add a noticeable amount over a year. Use the price you actually pay per kWh, including taxes.
Formula
E = m × c × ΔT (c = 4.186 kJ/(kg·K)) · t = E ÷ (P × η)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
v | Volume | L |
t1 | Starting water temperature | °C |
t2 | Target temperature | °C |
p | Power of the heater | kW |
ef | Efficiency | % |
pr | Energy price per kWh | /kWh |
TM | Heating time | min |
TH | Heating time in hours | h |
EK | Heat put into the water | kWh |
CO | Cost of the energy used | — |
Worked example
- Volume100 L
- Starting water temperature15 °C
- Target temperature60 °C
- Power of the heater2 kW
- Efficiency95 %
- Energy price per kWh0.2 /kWh
- Heating time165.2 min
- Heating time in hours2.75 h
- Heat put into the water5.233 kWh
- Cost of the energy used1.10
Limitations
- Prices and emission factors are yours to enter. The tool ships with no tariff table and assumes nothing about your country or supplier, so change the defaults to match your own bill.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.