Knowledge Base

How Many Watts Does an Electric Tankless Water Heater Use? (Power Consumption Test)

By:Michael Johns

tankless water heater power header

On this page, you will find out how many watts an electric tankless water heater draws.

As the world moves away from fossil fuels into renewable energy, the appliances we install in our homes are changing. It’s likely you’ve switched or are considering an electric tankless water heater. These devices are heralded for their 100% efficient and instant hot water delivery. But what is the actual power consumption?

Below we will discuss and test electric tankless water heater wattage, explain how to work it out for yourself, and calculate the total electricity required.

How Many Watts is an Electric Tankless Water Heater?

The average electric tankless water heater uses between 7,000 and 12,000 watts. That’s 7 to 12 kilowatts!

The exact number depends on the size and model of your tankless water heater. For example, a smaller water heater designed to supply a single outlet uses around 7,000W. Larger models required to supply multiple outlets reach 12,000W and more!

You can clearly see that the size of your instant water heater directly impacts its power usage. The higher the water flow and more outlets you need to supply simultaneously, the more powerful the heater. This is because it contains larger heating elements that are required to heat a bigger volume of water. And the bigger the heating elements, the more power they consume.

How to Find Out Your Electric Tankless Water Heater Wattage

There’s 3 ways you can work out the wattage of an electric tankless water heater.

  1. Check Product Specification

The quickest way is to look at the electric tankless water heater’s specification. The watts (W) is usually written on a sticker on the base of the appliance. If not, you can check the user manual or the manufacturer’s website for technical details.

tankeless water heater power specs
  1. Wattage Formula or Calculator

If you know the amperage and voltage of your electric tankless water heater you can use this to find the maximum watt rating. Simply use the formula Amps x Volts = Watts. Or you can head over to the ‘Watt Calculator’ to work this out.

Tankless Water Heater Wattage Examples

Let’s take a look at specific examples of how many watts an electric tankless water heater draws. Below is a collection of modern electric tankless water heaters with their listed power ratings.

Tankless Water Heater ModelPower Rating (Watts)
Heatrae Sadia Multipoint 7kW Instantaneous Water Heater7000
Redring Powerstream 12kW Unvented Instantaneous Water Heater12,000
Zip Inline ES3 Electronic Instantaneous Water Heater2800
Stiebel Eltron DHM 3 Unvented Instantaneous Water Heater3500
Stiebel Eltron DHC-E Unvented Instantaneous Water Heater9600
Redring Powerstream 9.5kW Unvented Instantaneous Water Heater9500
Triton Instaflow 5.4kW Single Point Instantaneous Water Heater5400
Stiebel Eltron DHM 4 Unvented Instantaneous Water Heater4400
Stiebel Eltron DHM 6 Unvented Instantaneous Water Heater5700
Triton Instaflow 7.7kW Single Point Instantaneous Water Heater7700
Triton Instaflow 10.1kW Single Point Instantaneous Water Heater10,100
Stiebel Eltron DHB-E 18/21/24 LCD Set Instantaneous Water Heater18,000
Stiebel Eltron DCE-S 10/12 Plus Instantaneous Water Heater10,000

As you can see, the power ratings vary between different electric tankless water heaters. So you should take the time to check your own appliance.

How Much Electricity Does an Electric Tankless Water Heater Use?

You can use electric tankless water heater wattage to work out how much electricity it uses. Plus this can be useful in understanding how much it costs to run your electric tankless water heater.

A watt (W) is a measurement of power at a single point in time. A watt-hour (Wh) is the total amount of electricity used in an hour. For example, an electric tankless water heater drawing 12,000W would use 12,000Wh when running for an hour.

Happily, electricity bills are recorded in kilowatt-hours (kWh). A kilowatt is simply 1000 watts. So a 12,000W electric tankless water heater running for 1 hour uses 12kWh.

In reality, you use an electric tankless water heater for 30 minutes a day. This means a dual outlet electric tankless water heater uses about 6000Wh or 6kWh electricity a day. That’s 180kWh a month and 2190kWh a year. 

That’s a rough electricity cost of $0.90 a day or $328.50 a year to heat water for 30 minutes every day.

Using an Electric Tankless Water Heater Off-Grid

If you’re planning to use your electric tankless water heater in an off-grid situation, like a power outage, the information above is important. You can install the correct electrical equipment and calculate the total runtime.

You can either use a power inverter or generator for AC electricity. 

To make sure everything runs smoothly you should check two things on this equipment – wattage capacity and total energy capacity. 

Your power source, like an inverter, should have a wattage capacity of at least 20% more than your electric tankless water heater. This ensures it will be able to deliver enough power as they are never 100% efficient. 

Secondly, you need to ensure your energy source, like a battery, has enough energy to run the electric tankless water heater for the required amount of time. It could use 2000Wh electricity for 10 minutes usage. This is the equivalent to 166Ah on a 12V battery.

How Many Watts Does an Electric Tankless Water Heater Use Summary

I hope you clearly understand how many watts an electric tankless water heater uses.

Installing these appliances is a step to living in a more efficient way. You should be aware that it will be the biggest electricity consumer in your home. Yes, they are 100% efficient in converting electrical energy into heat. But this still requires a lot of power! 

Electricity usage certainly spikes when you turn the hot water tap on. Of course, this means a higher electricity bill but you’ll be saving on your gas bills. If you’re thinking about running off-grid when there’s no mains power, be prepared with a serious generator or battery backup.