Overview of the water heater calculator

This water heater calculator provides an approximate heating time for various heater configurations. Select the amount of water in the tank, the temperature change required, and the size of heaters installed, and the calculator will provide a heating time in minutes.

This calculator assumes 100% efficiency, which is typical for immersion water heaters, but if you know your system has an efficiency less than 100%, provide a proportionally less number for 'watt output'.

Key data required for determining the amount of time to heat up water

1. Volume of water being heated

The volume of water being heated should be entered and either Liters or US Gallons selected. The more water that is present, the longer the heatup time will be for a given power input.

2. Water temperature change required

The amount of temperature change required. Start with the final temperature the water needs to be, and substract the starting temperature of the water. This gives the number of degrees (in either Celsius or Fahrenheit) that the water temperature will need to change. 

3. Watt output of the heater(s) being used

The third and final input is the amount of power that will be heating the water. Enter the number of watts of the heater. If not certain, the specifications of the heater should be written on the side of the heater and the watts given at a set voltage. For example, the heater will say 5500W at 240V. This means that at 240V power supply, the heater will provide 5500W heating power. At lower voltage, the watts will be less. If the heater is too hard to access to look at the specifications, the power can be determined by using an amp meter to determine the amps passing through the wires going to the heater, and multiplying it by the supplied voltage. For example, if the amp meter indicates 22.8A, and the voltage is 240V, multiply 22.8A by 240V will give 5472W. A multimeter can be used to confirm voltage.

Entering these three data sets in the water heating calculator above will provide you an estimate for the total time to heat your water.