Water Heating Time Calculator

Calculator that tells you how long it takes to heat water from start to end temperature with a given heating power.

Other water heating calculators are: power and energy.

The calculator supports Celsius/Centigrade, Fahrenheit, Watts (w), Kilowatts (Kw), Btuh, Joule, British thermal unit (Btu), liter, gallon, kg, lb, cubic inch, cubic foot etc.

The calculator supports decimal numbers, use dot or comma.

Amount of water
Start temperature
End temperature
Heating power

If you are using the calculator for swimming pool heating, please add a sufficiently large margin of safety to compensate for all the heat losses.


The formula to calculate the heating time of water is as follows:

(amount of water in kg) • (end temperature in °C – start temperature in °C) • (4168 joules/kg/°C)
(heating power in watts)
= heating time in seconds

To use the formula:
1) calculate the weight of water in kg
2) multiply that with the temperature difference in Celsius
3) multiply that with the constant of 4168
4) divide that by your heating power in watts
and the result is the heating time in seconds.

4168 is the constant for the heat capacity of water and means that it takes 4168 joules of energy to increase the temperature of 1 kilogram of water by 1 degree Celsius.

The heating power is in watts in the formula. A watt is defined as joules per second, e.g. 1W = 1 j/s = 1 joule per second.


Comment by gtcfoadm on Nov 22, 2019
Comments for the page: https://gettopics.com/en/calc/water-heating-time
Comment by Mike on Sep 3, 2020
A continuous flow calculator for instant water heaters would be useful, e.g. DHW gas boilers, electric showers, so that temperature rise for a given flow rate could be calculated, or input power needed to achieve a target Δ° at a particular flow rate, etc.
Comment by Jawad on Jan 5, 2021
Thanks for the calculator! very helpful

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