tankless electric water heater power consumption

If you are planning to buy a new tankless water heater or wondering how much electricity your existing tankless water heater is consuming then this article is for you. In this article, we will calculate the power consumption of a tankless water heater and also look at how much it costs to use one.

Also by the end, you will learn to calculate the power consumption of any electric water heater using a simple calculator.

Tankless water heaters are normally rated between 2 kW to 30 kW. Generally, the higher the wattage, higher is the flow rate and quicker it can heat the water. A 8kW tankless water heater running for 30 minutes a day will consume around 4 kWh of electricity in a day. This adds up to around 120 kWh of electricity in a month.

This would roughly translate to a monthly electricity cost of $ 19.44 in the US, £ 43.20 in UK, C$ 18.72 in Canada and Rs 1,200 in Mumbai, India.


Tankless Water Heater Power Consumption:

The power consumption of a tankless water heater (for that matter any electrical appliance) depends upon two main things,

  1. First is the wattage of your tankless water heater,
  2. And second is the electricity tariff in your area.

Before we jump into calculating the power consumption of your tankless water heater let’s see what these terms are and how you can find out your tankless water heater’s wattage and the electricity tariff of your locality.

If you already know these terms and just want to use the calculator then please scroll down to use the calculator.


What is the Wattage of a Tankless Water Heater:

Tankless water heaters are rated between 2 kW to 30 kW. Generally, the higher the wattage, the quicker it can heat the water, the higher the flow rate, and the higher the power consumption.

You can find the wattage of your tankless water heater by reading the label on it or just look for your tankless water heater on amazon and you will find its wattage in the description section.

(If you don’t have time to do this, then don’t worry I have put together a table at the end that shows the power consumption of a range of tankless water heaters with different wattages.)

If you don’t know what a watt is then here is a quick explanation,

Watt is the unit of power. It means the rate at which electricity is consumed or produced by a device. For example, a 50-watt TV consumes power at a rate of 50 watts per hour, it does not mean that the TV consumed 50 units of electricity, it means it will consume power at a rate of 50 watts every hour.

So in short, the wattage of a tankless water heater lies between 2 kW to 30 kW and you can find it by looking at the label on it. With that out of the way, let’s look at what is electricity tariff.


What is your Electricity Tariff:

In simple words, electricity tariff is the amount your electricity provider charges you for one unit (kWh) of electricity. I live in Mumbai, India here the electricity tariff is Rs 12/kWh.

(What is a Kilowatt hour (kWh) Kilowatt hours or units of electricity is the energy consumption of a device. For example, a 50-watt table fan running for 50 hours will consume 50 watts x 50 hours = 2500-watt hours = 2.5-kilowatt hours of electricity = 2.5 units of electricity. (1 kWh of electricity = 1 unit of electricity))

To find your electricity tariff, just look into your previous month’s electricity bill and find out your monthly electricity consumption, then just divide your monthly electricity consumption by your total monthly electricity bill, the figure you get is approximately your electricity tariff.

I have put together the following table that shows the electricity tariff of a few countries.

Electricity Tariff Around The World:

CountryElectricity TariffCountryElectricity Tariff
United States$ 0.154/kWhIndiaRs 6/kWh
United Kingdom£‎ 0.27/kWhGermany€ 0.44/kWh
CanadaC$ 0.30/kWhPhilippines₱ 9.70/kWh
AustraliaA$ 0.32/kWhSouth AfricaR 2.558/kWh

You can also check out the following resources to know your electricity tariff:


Calculate Tankless Water Heater Power Consumption:

With these two pieces of information in hand, you are ready to find the power consumption of your tankless water heater.

Let me show you an example,

tankless water heater power consumption
Rheem Tankless Water Heater: 8 kW

I have selected an 8 kW tankless water heater from Rheem listed on amazon.

Let’s assume we will use this 8 kW water heater for 30 minutes every day throughout the year.

Hence, we will calculate the daily, monthly, and annual power consumption of this 8 kW tankless water heater.

With the knowledge of your tankless water heater wattage and your electricity tariff, just use this simple formula to calculate power consumption.

Power consumption of an appliance = Wattage of the appliance X operational hours

Cost to run an appliance = Power consumption of the appliance X electricity tariff

(Operational hours is basically the number of hours you are using your tankless water heater)

Now let’s calculate,


How Much Power Does A Tankless Water Heater Consume:

In our case, wattage is 8 kW and operational hours are 30 minutes a day, 15 hours in a month, and 182 hours in a year.

Hence by using the above formula.

Power consumption of an 8 kW tankless water heater in a day (30 min) = 8 kW X 0.5 hours = 4 kWh

Similarly, Power consumption of an 8 kW tankless water heater in a month (30 min/day @ 30days) = 8 kW X 15 hours = 120 kWh

And Power consumption of an 8 kW tankless water heater in a year (30 mins/day @ 365 days) = 8 kW X 182 hours = 1,456 kWh

Now that we know the power consumption just multiply it by your electricity tariff and you will get how much it will cost you to run your tankless water heater.

let’s calculate how much it will cost to run this 8 kW tankless water heater for 4 hours every day for an entire month in the US, UK, Canada, and Mumbai.

  • In the US, the avg. electricity tariff is around 16.20 cents per kWh, hence it will cost around $ 19.44 (120 kWh X 16.20 cents) to run this 8 kW tankless water heater for 30 minutes every day for an entire month in the US.
  • In the UK, the avg. electricity tariff is around 36 pence per kWh, hence it will cost around £ 43.20 (120 kWh X 36p/kWh) to run this 8 kW tankless water heater for 30 minutes every day for an entire month in the UK.
  • In Canada, the avg. electricity tariff is around C$ 0.156 per kWh, hence it will cost around C$ 18.72 (120 kWh X C$ 0.156/kWh) to run this 8 kW tankless water heater for 30 minutes every day for an entire month in Canada.
  • In Mumbai, India, the avg. electricity tariff is around Rs 10 per kWh, hence it will cost around Rs 1,200 (120 kWh X Rs 10/kWh) to run this 8 kW tankless water heater for 30 minutes every day for an entire month in Mumbai.

How Much Does it Cost To Run A Tankless Water Heater:

For your reference, I have calculated the cost to run this 8 kW tankless water heater for 30 minutes daily throughout the entire year in the USA, UK, Canada, Australia, and Mumbai, India.

Country (Tariff)Daily Power Consumption of a Tankless Water HeaterMonthly Power Consumption of a Tankless Water HeaterAnnual Power Consumption of a Tankless Water Heater
USA (16.20 c/kWh)4 kWh, $ 0.65120 kWh, $ 19.441,456 kWh, $ 235.8
UK (36p/kWh)4 kWh, £ 1.44120 kWh, £ 43.201,456 kWh, £ 524.2
Canada (C$ 0.156/kWh)4 kWh, C$ 0.62120 kWh, C$ 18.721,456 kWh, C$ 227.1
Australia (A$ 0.32/kWh)4 kWh, A$ 1.28120 kWh, A$ 38.401,456 kWh, A$ 465.9
Mumbai (Rs 10/kWh)4 kWh, Rs 40120 kWh, Rs 1,2001,456 kWh, Rs 14,560

If your country is not on the table, then just note down the power consumption and multiply your electricity tariff to get the running cost.

The above figures show the maximum power consumption of an 8 kW tankless water heater, however, the actual power consumption can be 10 % – 20 % lower than this.

Also, most of us use our water heater only during winter which lasts for 3-4 months in most places. Hence, your annual power consumption will be much less.


Electricity consumption for different Wattage tankless water Heaters:

For your reference, I have made the below table that shows the power consumption of a range of tankless water heaters having different wattages. I have assumed 30 minutes of daily operation for an entire year.

Tankless Water
Heater Wattage
Daily Power Consumption
(30 Minutes)
Monthly Power Consumption (15 Hours)Annual Power Consumption (182 Hours)
3 kW1.5 kWh45 kWh547 kWh
5 kW2.5 kWh75 kWh912 kWh
10 kW5.0 kWh150 kWh1,825 kWh
15 kW7.5 kWh225 kWh2,737 kWh
18 kW9.0 kWh270 kWh3,285 kWh
24 kW12 kWh360 kWh4,380 kWh

You can find the cost to run any water heater by multiplying the power consumption from the above table with the local electricity tariff.

Also as I said before, the above values show maximum power consumption of a tankless water heater, the actual consumption will be 10% to 20% less than this.

Now go ahead and use the below calculator to find out the power consumption of your tankless water heater.

Just type the wattage of your tankless water heater, hours of usage, and your electricity tariff, and let the calculator do the math for you.


Tankless Water Heater power consumption calculator:

If you are not happy with the approximate results and you want to know the exact power consumption, then I would suggest you buy a cheap Kill-A-Watt Meter from amazon.


Calculate the exact power consumption of any Water Heater using Kill A Watt Meter:

Kill A Watt Meter is a simple device that gives real-time data on the power consumption of any device.

You can check it on amazon using this link – Kill A Watt Electricity Usage Monitor

To use a kill-a-watt meter to calculate the power consumption of your tankless water heater, first, connect your tankless water heater plug into the kill-a-watt meter, and then plug the kill-a-watt meter in your wall socket and you are good to go.

Then start using your tankless water heater and you can see in real-time how many kWh (units) of electricity it is consuming.

You can check out these articles to know more about the power consumption of space heaters, and the power consumption of garage heaters.

Check out the following articles to know the power consumption of other appliances:

You can check out this article to know more about the power consumption of common household appliances.

Check out my articles on solar power for home and how it can help you save your electricity bill.

Thank you for reading.

Aavjo 👋


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