Did you know that a tankless water heater uses up a lot of electricity? Even tankless systems, which are more efficient than traditional tank boilers, use almost 17% of a home’s total electricity consumption, according to the US Department of Energy.

Tankless water heaters are some of the most energy-hungry home appliances, so it’s essential to know just how much power they use. It would help if you also considered whether a natural gas tankless water heater or propane tankless water heater would be more efficient for your needs.

A tankless water heater uses between 20 and 50 kWh per month, depending on the size of the unit and the amount of hot water used. 

How Many KWH Does A Tankless Water Heater Use Per Month?

Let’s start with some rough estimates. A family of four in a mid-size house requires an electric tankless water heater with a heating capacity of at least 18 kW.

Tankless water heaters remain inactive most of the time, only turning on when hot water is needed. They also rarely operate at full capacity, so while it may draw 18 kW for the first 30 seconds of usage, it will require less energy to run overall.

A family of four uses around 50 gallons of hot water each day. Traditional tank heaters may require many hours to meet this need, while tankless heaters are considerably more efficient. Consequently, this household will probably only need a single kilowatt-hour of power each day for their heater.

The heater, on average, runs at half capacity. If we assume that the average cost of electricity across the US is 15 cents per kWh, then:

1. They can expect their electricity usage to be about 9 kWh daily, or $1.35.
2. Every month, that’s 270 kWh or 40 dollars.
3. Per year, that’s 3285 kWh or 493 dollars.

The standard cost of a water heater is around $510, which includes installation. However, when determining exactly how much energy your home consumes each year, you must keep in mind that it depends on how many hot water outlets are in your house and the ambient climate and your usage habits. Across states, the price of electricity does a tankless varies by several cents per kWh:

1. If you live in an apartment or with only one other person, expect to use less power than the preceding number indicates.
2. If you reside in a lower electricity cost state, you likely use much less energy than the prediction above.
3. If you live in a cold-weather state with high power prices, expect to use more electricity than the estimate above.

Most electric heaters are efficient, meaning that almost all the energy goes towards actually heating water. Thus, calculations are more straightforward as you don’t need to account for wasted energy.

For the cost of $0.1319 per kWh for electricity, we can determine how much it costs to operate an electric tankless heater each month and each year:

Why Do Electric Tankless Heaters Need Such High KW?

At first, it may seem strange that supposedly efficient products come with high kW requirements. However, electric tankless heaters achieve their efficiency by using a lot of energy to heat water quickly.

To put it in perspective, a sizable electric tankless water heater uses up to 36kW when heating water. That’s a big difference compared to the average dishwasher, which only consumes around 1.8kW. Although tankless heaters need power for less time (usually under 10 seconds), most home hot water appliances, including old-style tank heaters, run for hours at a time. While a tank heater uses water all day long even when you’re not using hot water, tankless heaters quickly do their job and then go into resting mode. As a result, they save around 40% on energy costs in the long run.