How to choose an Electric Tankless Water Heater

Deciding on 4 essential electric heater features will help identify the ideal tankless water heating system for your home. These are: flow rate, heating power, heater type, and brand reputation.

Flow rate

Flow rate is the output of a heater, listed in gallons per minute (GPM). Choose a heater with a high enough flow rate for your home’s needs. We recommend tankless heaters with a flow rate of at least 4 GPM.

A single shower or laundry machine requires about 2 GPM, and most 2-bathroom homes can operate comfortably on 4 GPM. Larger houses may need up to 10 GPM.

Heating power & efficiency

Heating power is the amount of energy an electric heater can deploy, listed in kilowatts (kW). For the majority of homes, we recommend a heating power of at least 18 kW.

Higher kW models quickly heat large amounts of water but need multiple circuit breakers and 240 volts. Lower kW heaters have less power but make fewer demands on your home’s wiring.

All electric heaters are highly energy-efficient and operate with minimal wastage. Most gas tankless water heaters can only achieve 80-90% efficiency, while electric models often reach 98% or higher.

Remember that heating power is affected by source water temperature. Heaters in colder climates may not meet manufacturer performance claims, so you may need to invest in a unit with a higher kW.

Heater type

There are two main types of tankless water heater: point of entry and point of use. Point of entry (POE) heaters are installed on a mains water line and provide heating for an entire home. They need high heating power and a strong flow rate to send water to multiple appliances.

Point of use (POU) heaters are installed by a single faucet or shower and heat water for that appliance only. POU products are smaller, less expensive, and need less electrical power.

POE heaters are more popular and convenient but require a modern service panel and wiring, so they’re not appropriate for every home. POU heaters may be more suitable for guest cottages, cabins, or homes with a low incoming water flow.

Warranty and brand reputation

Analysis from the US Department of Energy shows that most tankless electric heaters will last for around 20 years with proper installation and maintenance—far longer than the average tank heater.

Despite their longevity, it’s important to buy your heater from a brand with a reputation for reliability. Lifetime warranties and satisfaction guarantees are good ways to identify trustworthy manufacturers.

When comparing warranties, watch out for fine print restrictions. Many heater warranties are void if the unit is not installed by a licensed contractor.

Our top picks

1. Best Electric Tankless Water Heater for mid-size homes – Ecosmart ECO 18 Electric Tankless Water Heater

Ecosmart ECO 18 review:

Small but mighty, the Ecosmart ECO 18 is the heater we think offers the best value for homes with a maximum of 2 bathrooms. The ECO 18 heats up to 140 Fahrenheit and provides 4.3 GPM in mild climates, which is ample for two standard appliances running simultaneously. We like how the heater’s sensor activates at just 0.25 GPM, which means it won’t shut off at unwanted times, such as when adjusting the hot water during a shower. A digital control and 99.8% efficiency rating ensure that the ECO 18 doesn’t feel inferior to the pricier and more well-known Stiebel and Rheem (below). Reviewers highlight how user-friendly and extremely quiet the ECO 18 is, while Ecosmart provides customers with a limited lifetime warranty for peace of mind. To top things off, the ECO 18 is ETL and Water Quality Association-certified for safety. –Our Best Buy pick!

We recommend the Ecosmart ECO 18 for:

• Average-size homes (1-2 bathrooms)
• Energy saving
• Constant temperature (self modulating)

Or read our full review of the Ecosmart ECO 18

2. Best Electric Tankless Water Heater for larger families – Stiebel Eltron Tankless Water Heater Tempra 36

Stiebel Eltron Tempra review:

The Stiebel Eltron Tempra is the most well-reviewed tankless electric water heater on the internet—with good reason. It provides hot water in seconds and keeps a consistent flow thanks to self-modulating technology that automatically manages output during high-demand periods. This version of the Tempra provides an impressive 36 kW and up to 7.5 GPM, which is the most powerful heater on this page. It can run 4 showers simultaneously and exceeds the daily needs of most users, including those living in colder areas of the country. All that power does however mean the Tempra requires three 50 amp circuit breakers to safely run, which may require alterations to your wiring. The Steibel is manufactured in Europe to ANSI-certified standards and has a digital screen with programmable memory. Not to mention it’s super energy efficient and near-silent! The well-reviewed warranty includes 7 years of leak coverage—but is void without a professional install.

We recommend the Stiebel Eltron for:

• Consistently high water temperature
• Colder climates
• Larger families (3+ bathrooms)

Or read our full review of the Stiebel Eltron Tempra

3. Best point of use / RV / Mini Electric Water Heater – Bosch Electric Mini-Tank Water Heater Tronic 3000 T 4-Gallon

Bosch Tronic review:

The Bosch Tronic 3000 is not actually a tankless heater! But we think it’s a perfect point-of-use device from a renowned German company. With a 4-gallon tank, the Tronic 3000 is small enough to fit anywhere and reviews suggest there’s no delay in providing hot water—meaning it effectively operates like a tankless unit. It will run low if overused, but when connected to a single appliance in shower stalls, cabins, or RVs, its sub-hour refill time means that shortages shouldn’t be a serious problem. We recommend the Bosch and other POU heaters for guest accommodation, as a secondary heater, or in properties with a very low incoming GPM. Because it plugs into a standard 120V outlet, it’s a versatile unit with endless potential applications. On the downside, its low power does mean flow rate may be more impacted by incoming water temperature.

We recommend the Bosch Tronic for:

• Single appliance use (shower, kitchen sink)
• Lower electrical demands
• RVs, sail boats, cabins

4. Best US-designed Electric Tankless Water Heater –
Rheem RTEX-18 18kW 240V

We recommend the Rheem RTEX for:

• Average-size homes (1-2 bathrooms)
• Energy saving

Or read our full review of the Rheem RTEX-18

🔥Other popular Electric Tankless Heaters

Best for bathrooms – ECOTOUCH Tankless Water Heater

One of the smallest tankless heaters on the market, the ECOTOUCH can be used as either a point-of-use or point-of-entry system under the right conditions. One-touch buttons and a clear digital display control a copper heating element that produces up to 1.5GPM and 116 degrees with just 2% energy wastage. The ECOTOUCH is a great option for a single shower.

Learn more at Amazon >

Best for apartments – EcoSmart ECO 11 Electric Tankless Water Heater 13KW at 240 Volts with Patented Self Modulating Technology

The 13 kW version of our Best Buy pick, the Ecosmart ECO 18. This ECO 11 heater pulls off the feat of providing up to 3.1 GPM (enough for an apartment or small townhome) while running on a single 60A breaker. This makes it relevant for those who want to take advantage of lower electric bills, but can’t run a 240-volt system. Affordable, small, and stylish enough to install in a visible spot.

Learn more at Amazon >

Popular POU – Titan N-120 Electric Tankless Water Heater

An alternative to the Bosch Mini Tronic 300 is this Titan N-120. Able to run on 120 volts, it’s a versatile point-of-use heater that’s capable of handling a single appliance at a time. While it’s unlikely to cut it in colder climates, the Titan is a longstanding choice for simple, affordable water heating.

Learn more at Amazon >

Tiny proportions – Marey Power Pak Plus Tankless Electric Water Heater

Another highly affordable point-of-use heater, the Marey Power Pak Plus packs an impressive 2 GPM into a tiny casing that can be installed directly into a shower stall or kitchen cupboard.

Learn more at Amazon >

Best infrared heating – Sio Green SIO18 Infrared Electric Tankless Water Heater

Unlike the vast majority of electric tankless water heaters, which use copper coils to heat water, the Sio Green SIO18 contains an infrared laser that’s used to heat quartz crystals. Infrared heaters have a reputation for providing very high water temperature over a long lifespan.

Learn more at Amazon >

Popular in RVs – Stiebel Eltron DHC-E12 Tankless Electric Water Heater

This simple heater from Stiebel Eltron might not match the heating power of their Tempra unit, but it’s a good option for homes, boats, or RVs that only need limited amounts of hot water. A flow rate of 2 GPM should be ample for most showers.

Learn more at Amazon >

Best Electric Tankless Water Heater – Buying guide

How does a tankless electric water heater work?

To quickly raise water temperature and create the impression of endless hot water, tankless heaters contain flow sensors, which detect when an outlet in your home is turned on.

When the sensor is tripped, the heater supplies electricity to the heating element, which is either a series of copper coils or an infrared device. The opposite happens when an outlet in the home is turned off, meaning that no energy is wasted at hot water creation is truly “on demand.”

Copper coils are the most common way of raising water temperature in tankless water heaters and are also often the cheaper of the two main heating elements. The more coils within a heating unit, the hotter water can get.

Infrared technology tends to be more expensive than the traditional copper coil, but they aren’t necessarily better.

Selecting the right size tankless water heater

The most important consumer decision when buying a tankless water heater is unit size. the size of a heater determines its flow rate, which in turn determines the number of appliances the unit can simultaneously supply.

It’s easy to find out what flow rate your home requires. Simply make a list of your plumbed outlets and appliances, and each of their individual flow rates. Some appliances will list rates on their casing/service panel, while others require a quick Google search or guestimation.

Average flow rates for common appliances are:

• Kitchen faucet: 2.5 gallons per minute
• Bathroom faucet: 2.5 gallons per minute
• Shower Head: 2.5 gallons per minute
• Toilet: 1.6 gallons per flush
• Washing machine: 15-25 gallons per load
• Dishwasher: 8 gallons per load

Source: watereducation.org

No home runs all of its appliances at the same time, so think about the daily maximum flow rate you’ll need. Most homes can run happily on tankless water heaters with flow rates between 4-10 GPM.

For small to average-sized homes, we recommend the Ecosmart ECO 18, which delivers a flow rate of up to 4.3 GPM. For larger houses, our pick is the Stiebel Eltron, with a flow rate of up to 7.5 GPM.

When judging flow rate, consider the ambient temperature of your water source. The lower the temperature of incoming water, the harder the unit will need to work to keep the desired temperature and flow of water.

Most heater companies supply information on flow rate based on ideal incoming water temperature, so be sure to factor in the specifics of your environment.

Tell me the difference between a tankless and tanked water heater

Costs

Electric heaters without tanks are generally less expensive than gas or tank models, both in unit price and monthly costs.

Even where the base price of electric tankless water heaters is higher, the investment is usually offset by savings on utility bills.

Without a tank to store water, electric heaters increase their energy efficiency by only heating what’s necessary and reducing wastage (known in the industry as standby heat loss).

Hot water demand

Even though tanked water heaters have the ability to store up hot water, they’re more likely to leave you shivering in the shower or frustrated at the kitchen sink.

When the tank in a traditional heater runs low, it can take a long time for the system to replace the supply. This can leave you fretting about how much hot water has been used during a day.

A tankless water heater supplies water on-demand to create the impression of endless hot water (assuming you have the correct flow rate for your needs). This is especially true in heaters without tanks that have an advanced flow control function, to help modulate the release of hot water.

Size and energy savings

A conventional water heater has large, multi-gallon tanks and bulky heating elements. This means they need lots of space—usually a laundry cupboard or boiler room. Modern heaters can be mounted on a wall, or even inside a shower cubicle.

Conventional tank-style water heaters are always operating, which eats up fuel and leaves a mark on your energy bills. A tankless unit only turns on when there’s a demand for hot water, meaning that you should see savings on your electricity bill.

Lifespan

Almost all tankless units will last for longer than tank heaters due to fewer moving parts and a more efficient heating process. The best electric tankless water heaters are designed to last up to 20 years, while conventional type water heaters have a service life expectancy between 8 and 12 years.

This difference in design also means that a tankless water heater can usually be serviced or replaced more easily than older models.

Maintaining a tankless heater

Heaters come with basic filter screens to help keep dirt and particulate matter out of the unit. Clean this filter screen regularly to avoid clogging.

Flushing or “de-liming” a heater is an important maintenance task to keep the element inside a water heater clean of chemical deposits and optimally functioning. This is usually done with vinegar or bleach.

We recommend installing a water filter [LINK] on the incoming water line to protect the unit. Many people also choose to add water softener [LINK] to reduce the number of corroding minerals running through the water heater.