5 Best Electric Tankless Water Heaters (2021 Reviews)


Temperature Master is an Amazon Associate. As an Amazon Associate we earn from qualifying purchases. We may also earn commissions if you purchase products from other retailers after clicking on a link from our site.

Electric tankless water heaters are the best type of water heater for many people. They offer instant point-of-use hot water heating, save on energy costs compared to gas-powered alternatives, and provide great flow rates that should meet the needs of most households. 

The best electric tankless water heater for most people is the EcoSmart ECO 27. It offers a high flow rate, excellent energy efficiency, enhanced durability, multiple safety certifications, and an attractive warranty. 

This article will first take you through what you should consider when buying an electric tankless water heater. We’ll also discuss why the ECO 27 is the best choice for most people as well as provide alternatives that are better options in certain situations. 

What to Consider When Buying an Electric Tankless Water Heater

There are three primary factors that you need to consider when choosing an electric tankless water heater: 

  • Flow rate 
  • Temperature rise
  • Cost (Purchase, Installation, Energy, Maintenance, Repairs)

I’ll explain all three below:

Flow Rate and Temperature Rise

Understanding flow rate and temperature rise are essential to choosing the right water heater. If you mess this part up, you could end up not having enough hot water to run all of your appliances and water fixtures. 

What Flow Rate Do You Need?

Flow rate is the amount of water per minute that your water heater can heat up at once. This is measured in Gallons Per Minute (GPM). 

To figure out the flow rate you need, you have to figure out the flow rate of each appliance that needs hot water and add them all together. 

Here’s a chart with average flow rates for common appliances:

FixtureAverage Flow Rate (GPM)Average Temp. 
Bathtub 4.0 GPM102°F
Shower2.0 – 3.0 GPM104°F
Washing Machine2.0 GPM120°F
Dishwasher1.5 GPM110°F
Kitchen Sink1.5 GPM110°F
Source: CompactAppliance.com

Please note that these are estimates. To get an exact number, you can consult your appliance manuals. If you’ve lost your appliance manuals (as I’m sure most people reading this have), read this handy guide from The Spruce on how to manually determine your home’s GPM Rating

Note: You only need to worry about meeting your maximum flow rate (and thus purchasing a more powerful water heater) if you need to run all of your appliances and fixtures at the same time. If you’re okay with waiting to run the dishwasher or washing machine until after you’re finished taking a shower, you can get away with buying a less expensive unit. 

Your flow rate is also dependent on the temperature of the incoming water. You’ll only be able to achieve your maximum flow rate if your incoming water is relatively warm. 

If you live in a colder part of the country, your achievable flow rate will be lower than the maximum flow rate advertised by the manufacturer. I’ll get into this below. 

How Hot Does The Water Need to Get (Temperature Rise)?

To determine the true flow rate your hot water heater needs to provide, you’ll also need to know the “temperature rise,” or how much your hot water heater will need to heat the incoming water. 

The first step in this process is to figure out the temperature of your incoming cold water. 

Your incoming water temperature depends on where you live. To help you figure that, here’s a map of average groundwater temperatures in the U.S.:

Source: BradleyCorp.com

Once you know how hot your incoming water is, you can determine how much your electric tankless water heater needs to heat up that incoming water to meet the water temperature needs of your appliances. 

For example, I live in northern New Jersey. According to the temperature map, my groundwater temperature is about 47°F. 

I have a few appliances that need hot water, but the one that needs the hottest water is my washing machine, which needs 120°F water to work properly. 

To figure out the temperature rise my water heater needs, I would subtract the desired temperature (120°F) by the groundwater temperature (47°F). 

120°F – 47°F = 73°F. So my water heater would need to support a temperature rise of 73°F at my required flow rate.

Remember that temperature rise is not a standalone number – the flow rate you need to support all of your appliances affects it. 

The reason for this is simple: the more water you need to heat, the more energy needed to heat it. 

For example, a low-volume water heater might support a temperature rise of 73°F at 4.0 GPM. 

But if you need 8.0 GPM heated at a temperature rise of 73°F, you might be out of luck if you don’t have a high-power unit (or a pair of lower-power units). 

I’ll end this section with an easy rule of thumb: the further south you are in the United States, the lower the flow rate you’ll need. If you live in the north, you’ll need a more powerful water heater. 

Important Note: Electric Water Heaters Have Lower Flow Rates

The main downside to choosing an electric tankless water heater over a gas water heater is that the flow rates are considerably lower than gas alternatives. Electric options average 2 GPM,  while gas options average 5 GPM

So if you have a larger house where you might be using two showers, the dishwasher, and the washing machine at the same time, you’ll need to buy multiple electric tankless water heaters to make up for the lower flow rate. 

However, this isn’t necessarily a bad thing. Electric tankless models are typically half the cost of gas models. On top of this, they require much less maintenance (you’ll pay less for repairs) and have higher thermal efficiency and energy factor ratings (which saves money on energy usage). 

Cost (Purchase, Installation, Energy, Maintenance, Repairs)

The overall cost of your electric tankless heater is something you need to consider. And when I say overall cost, I’m not just talking about the initial purchase cost. You also need to consider installation costs, energy costs, and repair costs. 

Here’s a rough breakdown of what you can expect to pay:

  • Initial purchase cost: $250 – $1,200. The more powerful the heater, the higher the price. 
  • Installation cost: $800 – $1,500. You may also need to upgrade your home’s electrical service to 200+ amps to support the heater, as electric tankless heaters can draw up to 160 amps. 
  • Energy usage: ~$132 per year.  This cost will vary depending on how much your electricity costs per kWh and how much hot water you use. $132 per year is the average cost because the average monthly U.S. electricity bill is $115 and electric water heating represents 9.5% of residential electricity consumption. So the average electric water heater costs ~$11 per month or ~$132 per year. 
  • Annual flushing and cleaning: $200/year. Water heaters need to be flushed and cleaned once per year to prevent sediment buildup. 
  • Professional repairs: $150 – $800. Electric tankless units don’t break down often, but it can get expensive when they do. 

Our Top Picks

Prices pulled from the Amazon Product Advertising API on:


Best Overall: EcoSmart ECO 27 Electric Tankless Water Heater (240V / 27KW)

An excellent water heater at a reasonable price, the Ecosmart ECO 27 is the best option for most people. 

With a maximum output of 6.5 GPM, you’ll be able to run multiple showers and appliances without any trouble if you live in an area with warm groundwater. And even if you live in an area with frigid water, the minimum 2.7 GPM output is better than the average electric tankless heater. 

This heater also has a self-modulating flow sensor, which means it senses how much hot water you need and uses the minimum amount of electricity needed to heat it. Combined with a stellar 99.8% energy efficiency rating, this unit will save you a lot of money in energy costs compared to other electric tankless heaters. 

EcoSmart also offers a lifetime warranty on the ECO 27. To qualify for the warranty, you need a certified plumber OR a certified electrician to assist you with the installation. Note that the warranty only covers parts, not labor. 

Bottom Line: I highly recommend the EcoSmart ECO 27 if you’re looking for a powerful, high-quality electric tankless heater at a reasonable price. It will support the hot water needs of most American households, will last a long time with proper maintenance, and the self-modulation will maximize your electricity savings. 

Pros

  • Powerful. With a maximum flow rate of 6.0 GPM, this unit can support multiple appliances, showers, and faucets running simultaneously. 
  • Considerable energy savings. This unit doesn’t operate until it’s needed (so it’s not wasting energy in an “idle” mode when you’re not heating water. Combine this with the 99.8% energy efficiency, and you’ll be hard-pressed to find an electric water heater that saves you more money in energy costs. 
  • Very compact. This wall-mounted unit measures 17″ x 17″ x 3.75″ and is a mere 13.75 lbs. It’s easy to place in almost any environment – no matter how strapped you are for space. 
  • Precise temperature control. The digital interface allows you to set your temperature in increments of 1 degree. 
  • UL and CSA certified. This unit meets the stringent safety standards of UL (Underwriters Laboratories – a renowned global safety standards company) and CSA (Canadian Standards Association). 
  • Supports a remote thermostat. This unit doesn’t come with a remote thermostat, but you can buy an inexpensive waterproof remote thermostat for easy temperature control. 

Cons

  • Requires professional installation. This unit has some complex electrical components, and you’ll need a professional electrician to install it for you. EcoSmart also doesn’t offer the lifetime warranty unless the unit’s installation is certified by an electrician or plumber. 
  • Warranty doesn’t cover labor or incidental damages. EcoSmart will cover replacement costs for parts that wear out, but you’ll need to pay for the labor to install the replacements. 

Product Specs

Kilowatts27 kW
Voltage240 volts
Max Amperage112.5 Amps
Required Breaker3×40 Amps
Water Connections3/4″ NPT
Wire Gauge 3 x 8 AWG
Temperature Range 80°F – 140°F

Best Bang For The Buck: Rheem RTEX-13 Residential Tankless Water Heater (240V / 13KW)

The Rheem RTEX-13 is an excellent option if you’ve got a smaller home with limited hot water needs. 

This unit has a maximum flow rate of 3.17 GPM, which will support a hot shower, dishwasher, or washing machine with ease. You probably won’t be able to use multiple appliances at the same time, but the money you’ll save on the initial purchase and your electricity bill will make up for that. 

Installation is relatively easy, as you’ll only need one 60 amp 240 volt breaker (which your home likely already supports). The copper heating elements will also last a long time, provided you flush and descale the heater each year.  

Bottom Line: This unit is effective, affordable, and durable. If you live in a 1-2 person home, or if you’re looking for a dedicated heater for an appliance or faucet, the Rheem RTEX-13 is the way to go. 

Pros

  • Great for saving money. The RTEX-13 has an energy efficiency of 99.8%, and users have reported a 19% – 30% cost decrease in their monthly energy bills after installing it. 
  • Easier installation. You can likely install this unit yourself without the need to retrofit your wiring. However, proper installation does require electrical knowledge, so you may want to hire an electrician anyway. 
  • Very compact. This wall-mounted unit is 12.63 x 8.25 x 3.63 inches, and will fit on almost any utility wall setup. 
  • Durable heating elements. This unit comes with threaded copper heating elements, which are known for their durability. The fact that they’re threaded also makes replacing them very easy. 
  • 5-year limited warranty. Rheem offers a 5-year warranty that covers parts that fail due to a defect in materials or workmanship. 
  • Digital temperature setting. The digital interface makes it easy to read and change the temperature. 

Cons

  • Lower flow rate. With a max flow rate of 3.17 GPM, this unit is designed for homes with minimal hot water needs. If you have a family or a larger home, I recommend choosing something more powerful. 
  • Might need a showerhead with flow restriction. Some users have reported that shower water doesn’t heat up fully if it runs through the heater too quickly. To fix this, you may need to install a showerhead with a flow restriction component. 
  • Might not last 10 years. A few users have reported this unit needed replacing after 2 years of use. Annual flushing should improve its longevity, but you likely won’t get the 10+ years of service that come with higher-quality units. 

Best For Large Households: Stiebel Eltron Tempra 36 Plus

There’s no denying it – the Stiebel Eltron Tempra 36 Plus is a powerhouse in the electric tankless water heater game. With a maximum flow rate of 7.5 GPM, you’ll almost certainly be able to run all of your appliances and shower/faucet fixtures – even if you have a large household.

With 99% energy efficiency and self-modulating technology (which ensures the heater only uses energy when you need hot water), this unit will also provide significant energy savings despite its considerable output. 

Stiebel also offers a 7-year warranty on leakage and a 3-year warranty on parts replacement, so you’ll be covered if one of the components doesn’t meet durability expectations. 

Bottom line: If you have a larger household and want to be absolutely sure that you can run all of your appliances and fixtures simultaneously, the Stiebel Eltron Tempra 36 Plus is an terrific choice. 

Pros

  • Excellent flow rate. With a maximum flow rate of 7.5 GPM, you should be able to run all of your appliances and fixtures simultaneously. 
  • Great cost savings. 99% energy efficiency and self-modulating technology will ensure you get a lower electric bill. 
  • Silent operation. This unit is designed to operate in near-total silence. You won’t get that buzzing sound that other electric tankless heaters might emit. 
  • Excellent warranty. A 7-year leakage and 3-year parts warranty ensures you’re covered in the event of faulty manufacturing.
  • Trusted brand. Stiebel Eltron actually invented electric tankless water heaters more than 90 years ago, and their reputation for quality has only grown since then. 
  • Digital display. The digital interface makes it easy to control the temperature and understand what’s happening inside of your water heater. 

Cons

  • Tough to install. A more powerful heater means a more complex electrical system, and you’ll definitely need a professional’s help to install the Tempra 36 Plus. 
  • May need to replace plastic turbine. Some users have mentioned that a small, inexpensive plastic piece in the flow sensor wears out quickly. Replacement is easy and cheap, but it’s something you’ll need to worry about. 

Zero Maintenance Pick: SIOGreen Sio18 V2 Infrared

One of the most annoying parts of having a water heater is the required maintenance. If you don’t flush most water heaters at least once per year, the corrosion and sediment buildup will shorten the life of your heater significantly. 

The Sio18 v2 Infrared eliminates the need for yearly maintenance. The infrared heat technology (patented by SIO) doesn’t use metallic coils to heat the water, so there’s no metal for the water to corrode. You won’t have to worry about hiring a plumber to flush the heater or buying a descaling kit to do it yourself. 

The lack of corroded metal in the heater also ensures you have healthier water and don’t get higher energy bills because your heating elements aren’t operating at full capacity. 

This electric tankless water heater is a great option even if you don’t care about the zero maintenance aspect. Although it’s a bit bigger than some of the other options mentioned above (25 x 17 x 9.75 inches and 28 lbs), the maximum flow rate of 5.0 GPM is more than capable of handling all of your appliances and fixtures. This unit also self-modulates, so it’ll only activate and use energy when you need hot water. 

Bottom line: If you have hard water, the Sio18 v2 Infrared is the best option. Most households with hard water go through water heaters relatively quickly due to corrosion and sediment buildup, but this heater eliminates that problem entirely. 

Pros

  • No maintenance required. Infrared heating technology means you don’t have to worry about sediment buildup or heating element corrosion. 
  • Self-modulating. Like some of the other models mentioned, the SIO v2 only activates when you need hot water. 
  • 30-day refund policy. If you’re not happy with your purchase, SIO promises to give a full refund within 30 days after purchase. 
  • Compact and wall-mounted. Although a bit bigger and heavier than other electric tankless water heaters, it’s still a small unit that you’ll be able to mount on almost any wall. 
  • Decent flow rate. Although not as powerful as the Tempra 36 Plus, the 5.0 GPM max flow rate still makes this a powerhouse compared to most electric tankless water heaters.

Cons

  • Occasional manufacturing failures. A few users have found that their SIO heaters stopped working a few weeks after installation. However, this problem occurs very rarely, and the 30-day refund policy should cover any issues. 
  • No info on energy efficiency. SIO doesn’t provide information on their energy efficiency, so I can’t say for sure that this heater is as efficient as the other options mentioned above. 

Best for Commercial Usage: Stiebel Eltron 074056 Commercial

If you need a heavy-duty water heater that can provide a near-constant supply of hot water to a single point of use (such as a handwashing station or a utility sink), the Stiebel Eltron 074056 Commercial is a terrific option. 

Unlike most other electric tankless water heaters, this German-designed unit doesn’t try to offer a huge flow rate. Instead, this model offers a precise, consistent flow to one or two fixtures that see abnormally heavy use. The all-copper heating elements are quite durable, and this unit should last for many years – even with heavy use. 

Microprocessor technology ensures the temperature doesn’t deviate from what you set it to, which is important for a great customer experience (nobody likes water that is too hot or too cold – especially in a place of business). This makes it great for commercial settings like a public bathroom in a restaurant or an office building. 

It’s also very lightweight and compact (19 x 7.9 x 14.25 inches and 6.6 lbs) and has a modern design, so it won’t be intrusive or unattractive. And a hydraulic design ensures it’s as quiet as possible, so your customers won’t hear any annoying buzzing sounds. 

Bottom line: If you need a consistent, precise water heater for sinks or showerheads in an office or place of business, the Stiebel Eltron 074056 is a great option. It’s relatively inexpensive, durable, and unobtrusive compared to other electric water heaters on the market. 

Pros

  • Precise temperature control. This unit uses a microprocessor to ensure the temperature of your water doesn’t deviate from the temperature you set it at. 
  • Self-modulating technology. This model also self-modulates, so it won’t activate and use energy unless the sink or shower it’s attached to is turned on. 
  • Quiet operation. The hydraulic system ensures it makes as little noise as possible. 
  • Very durable. The all-copper heating elements should last a long time with proper maintenance. 
  • Easy to install. Because this is a lower-power device, you likely won’t need to retrofit your wires to install it. 
  • Scalding protection. The 074056 has built-in failsafes to ensure the water temperature can’t reach dangerous levels, which is especially important from a liability standpoint. 
  • Limited warranty. Stiebel Eltron offers a 3-year limited warranty if your heater is installed by a professional. 

Cons

  • Low flow rate. This unit only has the capacity to support a few sinks. If you need to support multiple appliances, you should pick a different water heater. 
  • Potential for manufacturing problems. A few users have reported that faulty manufacturing resulted in their heater breaking down after a few months of use. However, this issue seems to be very rare. 

Final Thoughts

After considering purchase price, GPM output, energy savings, and a host of other factors, I’ve found that the best overall electric tankless water heater for most people is the EcoSmart ECO 27

Compared to my other picks in this article (and the many that didn’t make it), the ECO 27 makes the most sense for the vast majority of people. 

The only instances in which I wouldn’t recommend it are if…

  • You have a very large household. Go with the Tempra 36 Plus (available on Amazon). 
  • You’re on a strict budget. Go with the RTEX-13 (available on Amazon). 
  • You have particularly hard water or want zero maintenance. Go with the Sio18 v2 Infrared (available on Amazon). 
  • You need a dedicated unit for commercial usage. Go with the Stiebel Eltron 074056 (available on Amazon). 

Click here to check out the ECO 27 on Amazon now. 

Steve Rajeckas

Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

Recent Posts