Best Electric Tankless Water Heater

Quick Summary

Choosing the best electric tankless water heater is less about picking a brand and more about understanding your local climate and your home’s electrical capacity. While these units save significant space and eliminate standby energy loss, they are not “plug-and-play” replacements for traditional tanks. In colder northern climates, even the most powerful electric units may struggle to provide hot water for more than one shower at a time because they must work significantly harder to heat near-freezing groundwater. For most whole-house applications, the Stiebel Eltron Tempra Plus series is the professional favorite due to its advanced flow control, while the EcoSmart ECO series offers a more budget-friendly entry point for those in warmer regions like Florida or Texas. Before buying, you must verify if your electrical panel can handle the massive 100-amp to 150-amp draw these units require.

What Real Users Are Saying (Reddit Insights)

The ‘Florida Rule’: Why Location is Everything

If you spend any time in plumbing forums or subreddits like r/askaplumber, you will quickly notice a divide. Users in Southern Florida, where groundwater often stays above 70°F, tend to love their electric tankless setups. One user on Reddit noted that they have used an ECO 27 for over a decade with high satisfaction because the starting temperature of the water is already “tepid.”

However, pros warn that as you move north, the “Florida Rule” takes effect. As groundwater temperatures drop into the 40s or 50s, the gallons-per-minute (GPM) capacity of an electric heater plummets. What handles two showers in Miami might barely handle a single low-flow showerhead in Chicago.

“Unless you live in southern Florida where the ground water is always at 70 degrees, electric tankless heaters are a waste of money… As the ground water gets colder, the GPM’s drop significantly.” — r/askaplumber

The Electrical Reality Check

The most common “hidden cost” discussed by homeowners is the electrical upgrade. A whole-house electric tankless unit often requires three or even four dedicated 50-amp breakers. For many older homes with 100-amp or 150-amp service, this necessitates a full panel upgrade to 200-amp or 250-amp service, which can cost more than the heater itself.

“It required three dedicated 50A circuits. Most houses around here only have 250A meters. You can do the math.” — r/Plumbing

Cons & Common Complaints

Beyond the installation hurdles, real-world users frequently cite three main frustrations:

• The “Cold Water Sandwich”: This occurs when you turn the water off and back on quickly. A small “slug” of cold water that was sitting in the pipes between heating cycles reaches you, leading to a brief, icy surprise in the shower.
• Hard Water Sensitivity: Unlike a tank that can hold a layer of sediment at the bottom for years, tankless heating elements are tiny and high-heat. In hard water areas, scale builds up rapidly, often leading to element failure within 5 to 7 years if a descaling maintenance routine isn’t followed.
• Maintenance Burden: You cannot ignore these units. Plumbers recommend a yearly flush with a descaling solution, which requires installing a service valve kit if the unit doesn’t come with one.

Best Electric Tankless Water Heaters by Use Case

1. Stiebel Eltron Tempra 24 Plus (Best Overall)

The Stiebel Eltron Tempra 24 Plus is widely regarded by professionals as the most “intelligent” electric tankless unit on the market. While most heaters simply blast the water with as much power as they can, the Tempra 24 Plus features Advanced Flow Control. If you exceed the unit’s capacity—say, someone starts a load of laundry while you are in the shower—the unit will slightly reduce the water flow to ensure the temperature stays consistent. It’s a much better experience than having the temperature suddenly drop to lukewarm.

✅ What Homeowners Love

• Sophisticated digital display for precise temperature setting.
• Advanced Flow Control prevents “cold shower surprises.”
• Solid German engineering with a very high reliability rating among plumbers.
• Silent operation compared to some humming budget models.

❌ Watch Out For

• Requires a minimum of 150-amp electrical service, but 200-amp is highly recommended.
• More expensive upfront than many competing brands.
• The “Plus” features are vital; the non-Plus versions lack the flow control technology.

💰 Street Price: $750 – $950

💼 The Verdict: Best for medium-sized homes in moderate climates where temperature consistency is the top priority. Skip if you have very high GPM demands and live in a snowy climate.

Check price on Amazon: Stiebel Eltron Tempra 24 Plus

2. EcoSmart ECO 27 (Best for Warm Climates)

If you live in the South, the EcoSmart ECO 27 is the “old reliable” of the industry. It provides up to 6 GPM in warm climates, which is enough to run two showers and a faucet simultaneously. It uses a patented self-modulating technology that only pulls the energy required for the specific flow rate you are using. If you’re looking for more ways to modernize your utility room, check out our guide on water heating systems for deeper dives into efficiency.

✅ What Homeowners Love

• Very affordable price point for the power output.
• Easy-to-replace copper heating elements available at most hardware stores.
• Compact design fits easily in small utility closets or crawl spaces.

❌ Watch Out For

• Requires three 40-amp breakers, which is a massive electrical footprint.
• Warranty is only valid if installed by a licensed professional—DIYers beware.
• Vulnerable to scale buildup; requires frequent flushing in hard water areas.

💰 Street Price: $400 – $500

💼 The Verdict: Best for Southern homeowners who want a powerful, well-supported unit without the premium price of German brands. Skip if you live in the North or have hard water and no filtration.

Check price on Amazon: EcoSmart ECO 27

3. Rheem RTEX-13 (Best for Small Cottages & Point-of-Use)

The RTEX-13 is not designed to run a four-bedroom house. Instead, it shines as a “point-of-use” heater or a solution for a tiny home or cottage with a single bathroom. Because it only requires a 60-amp service, it is much easier to retrofit into existing electrical setups without a full panel upgrade.

✅ What Homeowners Love

• Simple installation with standard 1/2-inch NPT connections.
• Small enough to fit under a sink or in a tiny bathroom cabinet.
• Reliable performance for single-fixture applications.

❌ Watch Out For

• Will only support one shower at a time (and only in warm climates).
• The 1.5 GPM flow rate in cold climates is very restrictive.
• Lacks the advanced modulation of higher-end Rheem models.

💰 Street Price: $400 – $500

💼 The Verdict: Best for guest suites, workshops, or tiny homes with minimal hot water demand. Skip if you expect to run a shower and a sink at once.

Check price on Amazon: Rheem RTEX-13

4. Stiebel Eltron Tempra 29 Plus (Best for Higher GPM Demands)

Stepping up from the 24, the Tempra 29 Plus is the “big brother” designed for larger families. It offers a higher kilowatt rating (29kW), allowing it to handle a higher temperature rise. This is the unit often recommended by plumbers for homeowners who are determined to go electric in cooler climates. If you are balancing this with other heavy electrical loads, browsing our heating and cooling solutions can help you plan your total home energy budget.

✅ What Homeowners Love

• Excellent performance in climates where groundwater hits 50°F.
• True “whole house” capacity for 2-3 bathroom homes.
• Same high-end flow control as the 24 Plus.

❌ Watch Out For

• Requires a whopping 120-amp draw (three 40A or two 60A breakers depending on config).
• Needs a 250-amp main service panel to be safe in most modern homes.
• Significant physical footprint compared to smaller point-of-use units.

💰 Street Price: $750 – $950

💼 The Verdict: Best for families committed to electrification who live in “moderate” rather than “tropical” climates. Skip if you only have 100-amp service.

Check price on Amazon: Stiebel Eltron Tempra 29 Plus

5. EcoSmart ECO 18 (Best Mid-Range Performance)

The ECO 18 is the “Goldilocks” of the EcoSmart lineup. It provides enough hot water for a small apartment or a 2-bedroom home in warmer climates, but it only requires two 40-amp breakers. This makes it much more likely to fit into a standard 200-amp panel without major reshuffling.

✅ What Homeowners Love

• Compact and easy to mount in tight spaces.
• Lower electrical requirement than the ECO 27.
• Reliable digital interface that allows for 1-degree temperature increments.

❌ Watch Out For

• Struggles if you have high-flow showerheads.
• Heating elements can be prone to “burning out” if the unit isn’t properly air-purged during install.
• Limited support for multiple simultaneous showers.

💰 Street Price: $400 – $500

💼 The Verdict: Best for condos or small households in the South. Skip if you have more than two bathrooms or live in the North.

Check price on Amazon: EcoSmart ECO 18

6. Rheem RTEX-18 (Best for Single-Bathroom Retrofits)

Rheem is a household name for a reason, and the RTEX-18 is their answer to the mid-sized tankless market. It is physically robust and often feels more “heavy duty” than the budget brands. In practice, the RTEX-18 delivers consistent heat for a single bathroom and a kitchen sink, making it a favorite for secondary dwellings or ADUs (Accessory Dwelling Units).

✅ What Homeowners Love

• External digital thermostatic control with LED display.
• Copper immersion heating elements are durable and easy to service.
• 99.8% energy efficiency rating.

❌ Watch Out For

• The display can be hard to read in dimly lit basements.
• Some users report a slight “whining” noise when the unit is at full capacity.
• Internal plastic parts can be fragile during the initial plumbing connection.

💰 Street Price: $400 – $500

💼 The Verdict: Best for those who trust the Rheem brand and need a reliable unit for a one-bathroom home. Skip if you want to run a whole house with 3+ people.

Check price on Amazon: Rheem RTEX-18

7. Eemax HomeAdvantage II (Best for Compact Spaces)

Eemax and EcoSmart are owned by the same parent company, but Eemax often targets the professional installer market. The HomeAdvantage II series is known for its incredibly small form factor. It is arguably the easiest unit to hide inside a bathroom vanity or a kitchen cabinet.

✅ What Homeowners Love

• Extreme space savings—about the size of a large shoebox.
• Active energy management system helps prevent flickering lights in the home.
• Very responsive tech support for installers.

❌ Watch Out For

• Can be more expensive than the consumer-focused EcoSmart equivalent.
• Spare parts can be harder to find at local big-box stores compared to Rheem.
• The warranty registration process is notoriously strict.

💰 Street Price: $400 – $500

💼 The Verdict: Best for high-end renovations where the unit must be hidden from view. Skip if you are looking for the cheapest possible DIY option.

Check price on Amazon: Eemax HomeAdvantage II

8. Black+Decker SATO Series (Best Budget Amazon Alternative)

A newer entrant to the field, Black+Decker has licensed their name for a series of tankless heaters that are aggressively priced. While it lacks the long-term track record of Stiebel Eltron, it provides a functional, digital tankless experience for hundreds of dollars less than the competition.

✅ What Homeowners Love

• The lowest price point for a “whole house” (18kW+) unit.
• Very modern look and easy-to-use interface.
• Surprisingly good flow rate for the price.

❌ Watch Out For

• Long-term durability is still an unknown in the plumbing community.
• The warranty support is not as robust as dedicated plumbing brands.
• Some users report internal leaks after the first year.

💰 Street Price: $150 – $250

💼 The Verdict: Best for budget-conscious homeowners or rental property owners looking for a quick, cheap upgrade. Skip if you plan to live in your home for the next 20 years.

Check price on Amazon: Black+Decker SATO Series

9. Navien NPE-240A (The Gas Alternative Recommendation)

I’ll be honest: many plumbers will look at your electrical panel and tell you to just go gas. If you have a natural gas line, the Navien NPE-240A is the gold standard of tankless. It solves the “cold water sandwich” problem with a tiny internal buffer tank and a recirculation pump. It is vastly more powerful than any electric unit.

✅ What Plumbers Love

• Built-in recirculation pump means hot water is “instant” at the tap.
• Can handle three showers simultaneously, even in the dead of winter.
• Ultra-high efficiency (0.95 UEF).

❌ Watch Out For

• Requires a gas line and complex stainless steel venting.
• Significantly higher installation cost (plumbing + gas + venting).
• Needs an annual professional service to maintain the warranty.

💰 Street Price: $2000 – $2500

💼 The Verdict: Best for large families in cold climates who have gas available. Skip if your goal is 100% electric home decarbonization.

Check price on Amazon: Navien NPE-240A

10. Camplux Propane Tankless (Best for Off-Grid/Cabins)

For remote cabins or off-grid sheds where you only have 50-amp solar power or a generator, an electric tankless heater is impossible. The Camplux portable propane series is the savior for these scenarios. It runs off a standard BBQ propane tank and uses D-cell batteries for the igniter.

✅ What Homeowners Love

• Can be set up anywhere in about 10 minutes.
• Extremely cheap to buy and run for occasional use.
• Perfect for outdoor showers or washing pets.

❌ Watch Out For

• Must be used in a well-ventilated area (ideally outdoors).
• You must drain it completely in the winter or the copper pipes will burst.
• Low water pressure can prevent the unit from igniting.

💰 Street Price: $400 – $500

💼 The Verdict: Best for off-grid cabins, camping, or horse barns. Skip for any permanent indoor residential application.

Check price on Amazon: Camplux Portable Propane

Best Electric Tankless Water Heaters Comparison

Product Name	Best For	Price Range	Pros/Cons	Visit
Stiebel Eltron Tempra 24 Plus (Best Overall)	medium-sized homes in moderate climates where temperature consistency is the …	$750 – $950	✅ Sophisticated digital display for precise temperat; Advanced Flow Control prevents “cold shower surpri ❌ Requires a minimum of 150-amp electrical service, ; More expensive upfront than many competing brands.	Check Price
EcoSmart ECO 27 (Best for Warm Climates)	Southern homeowners who want a powerful, well-supported unit without the prem…	$400 – $500	✅ Very affordable price point for the power output.; Easy-to-replace copper heating elements available ❌ Requires three 40-amp breakers, which is a massive; Warranty is only valid if installed by a licensed	Check Price
Rheem RTEX-13 (Best for Small Cottages & Point-of-Use)	guest suites, workshops, or tiny homes with minimal hot water demand	$200 – $250	✅ Simple installation with standard 1/2-inch NPT con; Small enough to fit under a sink or in a tiny bath ❌ Will only support one shower at a time (and only i; The 1.5 GPM flow rate in cold climates is very res	Check Price
Stiebel Eltron Tempra 29 Plus (Best for Higher GPM Demands)	families committed to electrification who live in “moderate” rather than “tro…	$850 – $1100	✅ Excellent performance in climates where groundwate; True “whole house” capacity for 2-3 bathroom homes ❌ Requires a whopping 120-amp draw (three 40A or two; Needs a 250-amp main service panel to be safe in m	Check Price
EcoSmart ECO 18 (Best Mid-Range Performance)	condos or small households in the South	$350 – $450	✅ Compact and easy to mount in tight spaces.; Lower electrical requirement than the ECO 27. ❌ Struggles if you have high-flow showerheads.; Heating elements can be prone to “burning out” if	Check Price
Rheem RTEX-18 (Best for Single-Bathroom Retrofits)	those who trust the Rheem brand and need a reliable unit for a one-bathroom home	$250 – $350	✅ External digital thermostatic control with LED dis; Copper immersion heating elements are durable and ❌ The display can be hard to read in dimly lit basem; Some users report a slight “whining” noise when th	Check Price
Eemax HomeAdvantage II (Best for Compact Spaces)	high-end renovations where the unit must be hidden from view	$200 – $300	✅ Extreme space savings—about the size of a large sh; Active energy management system helps prevent flic ❌ Can be more expensive than the consumer-focused Ec; Spare parts can be harder to find at local big-box	Check Price
Black+Decker SATO Series (Best Budget Amazon Alternative)	budget-conscious homeowners or rental property owners looking for a quick, ch…	$150 – $250	✅ The lowest price point for a “whole house” (18kW+); Very modern look and easy-to-use interface. ❌ Long-term durability is still an unknown in the pl; The warranty support is not as robust as dedicated	Check Price
Navien NPE-240A (The Gas Alternative Recommendation)	large families in cold climates who have gas available	$2000 – $2500	✅ Built-in recirculation pump means hot water is “in; Can handle three showers simultaneously, even in t ❌ Requires a gas line and complex stainless steel ve; Significantly higher installation cost (plumbing +	Check Price
Camplux Propane Tankless (Best for Off-Grid/Cabins)	off-grid cabins, camping, or horse barns	$200 – $300	✅ Can be set up anywhere in about 10 minutes.; Extremely cheap to buy and run for occasional use. ❌ Must be used in a well-ventilated area (ideally ou; You must drain it completely in the winter or the	Check Price

Technical Buyer’s Guide: What Plumbers Want You to Know

Calculating Your Flow Rate (GPM) vs. Incoming Water Temp

When you look at a box that says “4.5 GPM,” it usually assumes a 40-degree temperature rise (e.g., heating 70°F water to 110°F). But if you live in Maine and your winter groundwater is 38°F, you need a 72-degree rise to reach a comfortable shower temperature. This cuts your actual flow rate in half. Always check the manufacturer’s performance map for your specific zip code before buying.

Electrical Panel Requirements: 100A vs. 200A vs. 250A

The biggest mistake homeowners make is buying an ECO 27 or Tempra 29 and assuming they can just “add a breaker.” An electric whole-house heater can pull 120 amps on its own. If you only have a 100-amp panel, the heater will literally trip the main breaker the moment you turn on the hot water. In some cases, you may need to look into electric kitchen appliances that are more energy-efficient to “free up” room on your panel, but usually, a panel upgrade is the only safe way forward.

The Retrofit Challenge: Wire Gauges and Breaker Space

Installing a tankless unit is rarely a one-for-one swap. A traditional tank uses a 10-gauge wire and a 30-amp breaker. A tankless unit requires 6-gauge or even 4-gauge wire and multiple 40-60 amp breakers. Running that heavy-gauge wire from your panel to the bathroom or utility room can be a major construction project involving cutting through drywall and framing.

Vacation Homes: Tank vs. Tankless Debate

Energy Savings vs. Legionnaires’ Disease Risks

Vacation home owners often want tankless units because they don’t want to pay to keep 40 gallons of water hot while they aren’t there. While this saves money, a traditional tank sitting at 90°F for three weeks is a breeding ground for Legionella bacteria. A tankless unit eliminates this risk because no water is stored.

However, if you already have a working tank, the cheaper solution is often to install a smart switch or use “Vacation Mode.” If you’re looking for the absolute most efficient way to heat water in a full-time residence, we highly recommend reading our review of the best heat pump water heaters, as they can be 3x-4x more efficient than standard electric units.

The Case for Smart Switches on Traditional Tanks

If your panel cannot handle a tankless unit, you can mimic the energy savings by using a heavy-duty smart timer. You can turn the tank on via your phone four hours before you arrive at the cabin. This gives you the “off when away” benefits without the $2,000 electrical upgrade.

Frequently Asked Questions

Final Thoughts

Switching to an electric tankless water heater is a bold move toward home electrification, but it requires doing your homework on your home’s electrical capacity first. If you live in a warm climate, a unit like the EcoSmart ECO 27 is an easy recommendation. For those in colder areas, the Stiebel Eltron Tempra 24 Plus remains the safest bet for consistent performance. Always consult with a licensed electrician before purchasing to ensure your panel can handle the load.

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