Water Heater Power Consumption Calculator

Water heater gives us hot water on demand at the push of a button, but have you wondered how much power does a water heater consume and what effect does it have on our electricity bill, use this simple calculator to calculate power consumption of any water heater.

The rated power of a average size water heater is around 4000 watt or 4 kW. But its rated power vary from 1 kW to 15 kW depending on the size and the amount of hot water it can provide in short amount of time. A 4 kW water heater running for 20 minutes daily will consume 1.33 kWh of electricity in a day and 40 kWh of electricity in a month.

Water Heater Rated Power:

There are 2 types of water heater widely used for household purpose, one is on demand water heater (tank less) and other is conventional water heater with tank.

An on demand water heater or instantaneous water heater is designed to supply hot water on demand, meaning the moment you turn it ON in just 5 – 10 seconds you will start getting hot water. To achieve this, large amount of heat is supplied to the heating coil in very short time hence their power consumption is more. The larger the capacity of water heater, the higher is it’s wattage an higher is the power it consumes.

An average sized instantaneous water heat consumes around 4 kW of power.

Instantaneous Water Heater Wattage – Courtesy – Racold
Capacity Power
1 Litre3 kW – 4.5 kW
3 Litre3 kW – 4.5 kW
6 Litre3 kW

Conventional water heater features a tank that holds water to be heated. This means that the capacity of the tank determines how much hot water you have available at once. The tank is insulated so that when the water heats up, it remains warm until it is needed. Once you have used all the water in the tank it has to be heated again which takes time (depending on the capacity of heater).

Whichever water heater you have you can find it’s wattage by looking at the specification sticker on it’s bottom or just go to amazon and find you water heater or similar type water heater and check it’s wattage in product description.

My 4.5 kW Instantaneous Water Heater

Water Heater Power Consumption:

To calculate your water heater power consumption and interpret the results correctly you need to know and understand the following four parameters:

  1. Wattage: Wattage is the rate at which any appliance consumes power. For example a 1500 watt hair dyer consumes 1500 watt of power every hour.
  2. Operational Hours: Operational hours is the number of hours an appliance is in operation. For example a water heater running for 30 minutes mean it’s operating hours is 0.5 hours.
  3. Electricity Tariff: Electricity tariff is the amount your electricity provider charges you for one unit of electricity. I live in Mumbai, India here electricity tariff is Rs 12 / kWh. Whatever is the electricity tariff in your area type it in the electricity tariff tab.
  4. Unit Of Electricity (kWh): The power consumed by any device is measured in units of electricity or (kWh). For example a 3000 watt water heater running for 1 hour will consumes 3000 watt X 1 hour = 3000 watt hours or 3 kWh of electricity.

Now that you know all the above parameter it’s time to use the calculator below.

To give you a rough idea on power consumption, if you use a 4 kW water heater daily for 10 minutes then in the entire month it’s power consumption will be (4 kW X 0.166 hour X 30 days) 20 kWh.

The calculated results are approximate values and you can expect 10 % error on either side.

However if you are not satisfied with an approximate value and want to know exact power consumption of your hair dryer then can use a Kill A Watt meter to find it.

Calculate Power Consumption Of A Water Heater Using a Kill A Watt Meter

Kill A Watt Meter Courtesy – Google Images

Kill a watt meter is a simple device used to calculate power consumption of any device.

You can buy it from amazon using this link. Kill A Watt Electricity Usage Monitor

To use the Kill A Watt meter first connect your water heater plug to the Kill A Watt meter and then plug the Kill A Watt meter in your wall socket.

Then start using your water heater the way you do normally and you can see in real time how many kWh (units) of electricity your water heater is using.

Check out this tutorial video from altE to understand how to use a kill A Watt Meter to track your appliance energy consumption.


Water heater are consume lot of power if used for long time hence one should only use it when it’s necessary and the moment you are done using it turn it OFF immediately.

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