Online calculator

How to use the calculator, with examples.
Notes on water heating efficiency

Help

This calculator works out how much money, electricity and time it takes to heat water. You need no formulas or coefficients: just enter your data and get the answer. To calculate the electricity used, enter the cold and hot water temperatures and the water volume (mass). You can also enter the efficiency of the heater if you know it. With an efficiency of 100% the calculation shows only the useful energy spent on heating the water. With the real efficiency it shows the full energy taken from the grid. To work out the full cost of heating the water, enter your electricity tariff in UZS. To estimate how long heating takes, enter the power of the appliance that heats the water in kilowatts (kW). The power is often shown on the appliance itself and in its manual or data sheet.

Examples

Boiling water in an electric kettle

I usually fill the kettle with room-temperature water at 20°C up to the 1 litre mark and always bring it to the boil (100 degrees). The kettle is rated at 2 kW. A simple calculation shows that boiling takes about 0.1 kWh (kilowatt-hours) of electricity and about 3 minutes. The cost equals this 0.1 kWh multiplied by your tariff.

Heating water in a storage water heater

Every time I take a shower I use up all the hot water in the storage heater, because the water turns cold at the end. In winter the heater warms cold tap water from 5 to 45 degrees. The tank holds 80 litres. With 2 kW heating elements, fresh water in the tank heats up in about 2 hours, using about 4 kWh of electricity. In summer the water is heated from 18 to 45 degrees and use drops to about 2.5 kWh.
To find the cost of one shower, multiply these kWh by your tariff or enter the tariff in the calculator above.

Notes on water heating efficiency

There is a common misconception that electric water heaters are 100% efficient. It comes from the fact that theoretical calculations often ignore energy losses because they are small. But when calculations are used in practice, it is easy to see that energy losses in heating water begin in the very first seconds. Depending on the heater, they can include the following.

Main types of losses:

1. heating up the heating element itself (especially large for an electric hob);
2. heating the walls of the vessel (kettle, tank);
3. heat transfer and thermal radiation to the surroundings from the vessel walls and a non-immersed heating element;
4. evaporation from the water surface in open vessels (pots and kettles without a lid);
5. losses to steam when boiling (the largest loss channel);

From the main loss channels it is easy to see how to make water heating more efficient:

1. use an immersed heating element;
2. use a closed vessel;
3. insulate the vessel;
4. use the lowest temperature you actually need;
5. switch off when the water starts to boil;
   Additional losses include:
6. losses in electrical wires and contacts (heating of the wires and the appliance plug);
7. losses to side electrochemical processes (ion heaters, electrochemical decomposition of water, electrochemical dissolution of the anode);
8. losses to sound (the noise of steam bubbles where the heater or hot surface meets the water);