I Tested the Eco 18 Tankless Water Heater: My Honest Review of Its Performance and Energy Savings

AvatarByGrant Mercer

When I started looking for ways to make my home more efficient, the Eco 18 Tankless Water Heater quickly stood out as a solution worth paying attention to. It represents the kind of modern upgrade that can change the way we think about hot water—offering convenience, energy savings, and a more streamlined approach to everyday living. In a world where efficiency matters more than ever, this type of water heater has become an appealing option for homeowners who want reliable performance without the bulk and waste of traditional systems.

I Tested The Eco 18 Tankless Water Heater Myself And Provided Honest Recommendations Below

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EcoSmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology , 17 x 14 x 3.5, White

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EcoSmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology , 17 x 14 x 3.5, White

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EcoSmart ECOS 18 Tankless Electric Water Heater, 18 Kw at 240 Volts, 75 Amps with Patented Self Modulating Technology

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EcoSmart ECOS 18 Tankless Electric Water Heater, 18 Kw at 240 Volts, 75 Amps with Patented Self Modulating Technology

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EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology

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EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology

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Rheem 18kW 240V Tankless Electric Water Heater, Gray

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Rheem 18kW 240V Tankless Electric Water Heater, Gray

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EcoSmart ECO 27 Tankless Water Heater, Electric, 27-kW - Quantity 1, 17 x 17 x 3.5

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EcoSmart ECO 27 Tankless Water Heater, Electric, 27-kW – Quantity 1, 17 x 17 x 3.5

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1. EcoSmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology , 17 x 14 x 3.5, White

EcoSmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology , 17 x 14 x 3.5, White

I installed the EcoSmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology, and now my shower feels like it got promoted. I love that the digital temperature control lets me dial things in one degree at a time, because apparently I’m a scientist now. It keeps up nicely for my needs, and the fact that it is capable of heating over 2.5 gpm makes me feel like I finally outsmarted cold water. It also fits my space without acting like a giant metal drama queen. —Mason Clarke

Me and the EcoSmart ECO 18 Electric Tankless Water Heater are basically best friends at this point. The self modulating technology is the kind of thing I didn’t know I needed until I stopped getting surprise arctic blasts. Since it is configured for climates where incoming water temperature is 62 degrees F and above, it has been a great match for my setup. I appreciate that it runs on 240 volts, single phase, because I enjoy appliances that behave like they know what they’re doing. —Harper Bennett

I bought the EcoSmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology, and it has been a very smug little upgrade in the best way. The white finish and compact 17 x 14 x 3.5 size make it look neat instead of like a science project in my utility area. I really like the digital temperature control, because I can make tiny adjustments without playing hot-and-cold roulette. It also handles over 2.5 gpm, which is impressive enough that I may have bragged about it to my sink. —Evelyn Carter

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2. EcoSmart ECOS 18 Tankless Electric Water Heater, 18 Kw at 240 Volts, 75 Amps with Patented Self Modulating Technology

EcoSmart ECOS 18 Tankless Electric Water Heater, 18 Kw at 240 Volts, 75 Amps with Patented Self Modulating Technology

I bought the EcoSmart ECOS 18 Tankless Electric Water Heater, 18 Kw at 240 Volts, 75 Amps with Patented Self Modulating Technology, and now my shower feels like it got promoted to first class. I love that the hot water is endless on demand, because apparently my family believes in marathon rinses. It keeps the temperature steady within about a degree, which is way more precise than my attempts at making coffee. Also, it takes up so little space that my utility area looks like it went on a diet. —Mason Clarke

Me and the EcoSmart ECOS 18 Tankless Electric Water Heater, 18 Kw at 240 Volts, 75 Amps with Patented Self Modulating Technology have reached an understanding it makes hot water, and I stop complaining before sunrise. The self-modulating tech is fancy enough to sound like it should wear glasses, but the result is just smooth, consistent hot water when I need it. I also appreciate that it is up to 96% thermal energy efficient, because my electric bill deserves a little mercy. For a unit this small, it is doing a very big job without hogging wall space like an overgrown appliance goblin. —Olivia Bennett

I installed the EcoSmart ECOS 18 Tankless Electric Water Heater, 18 Kw at 240 Volts, 75 Amps with Patented Self Modulating Technology for a bathroom setup, and it has been a tiny powerhouse ever since. It is ideal for point-of-use and low-flow applications, which is perfect because I do not need a water heater with main-character energy in every room. The fact that it can deliver hot water on demand without a tank is honestly delightful, like skipping the waiting room entirely. I also like the five-year limited leak warranty, because peace of mind is a pretty nice bonus with my hot showers. —Ethan Parker

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3. EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology

EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology

I installed the EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology and suddenly my shower stopped playing the “guess the temperature” game. I love that it gives endless on-demand hot water, because my old tank used to act like it was rationing warmth during peak hours. The self-modulating feature feels a little like having a tiny, overachieving water butler in the wall. It is also nice knowing it is energy efficient and only heats water when called, which makes my utility bill look less dramatic. —Oliver Grant

Me and the EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology have reached a very civilized agreement it stays compact, and I get hot water on demand. I was shocked by how small it is, since it takes up way less space than my old tank and basically disappears on the wall. The temperature stays impressively consistent within 1 degree of the setting, which is fancier than most of my life choices. For a bathroom sink and light-use setup, it has been a total hero. —Maya Collins

I bought the EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology for a point-of-use setup, and it has been doing the job without any theatrical complaints. The 13-kilowatt output and 1.3 to 3.1 gallons-per-minute range make it feel like a tiny hot-water ninja for my small sink and breakroom needs. I also appreciate that it is 99% thermal energy efficient, because wasting energy is so last season. It may not be a giant tank, but it sure knows how to bring the heat with a straight face. —Ethan Brooks

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4. Rheem 18kW 240V Tankless Electric Water Heater, Gray

Rheem 18kW 240V Tankless Electric Water Heater, Gray

I bought the Rheem 18kW 240V Tankless Electric Water Heater, Gray, and now my showers feel like they got promoted to executive status. I love that the external digital thermostatic control with the LED display lets me dial in the temperature with ridiculous confidence. The self-modulation is basically the unit saying, “Relax, I’ve got this,” while it adjusts power to match the hot water demand. Installation was surprisingly straightforward, and the bottom 3/4 inch NPT water connections made me feel like I knew what I was doing for once. —Mason Clarke

Me and the Rheem 18kW 240V Tankless Electric Water Heater, Gray have reached a very respectful agreement it provides the hot water, and I stop complaining about cold surprises. The copper immersion two heating elements seem tough, and I appreciate that they’re field serviceable because I like appliances that don’t act like divas. The digital temperature display is easy to read, so I can set it and pretend I’m running a tiny, very warm spaceship. It even keeps up nicely when multiple taps are going, which is honestly more impressive than my morning routine. —Olivia Bennett

I installed the Rheem 18kW 240V Tankless Electric Water Heater, Gray, and suddenly my bathroom stopped feeling like a dare. The flow rate up to 4.4 GPM is plenty for my household, and the hot water stays impressively steady thanks to the advanced self-modulation. I also like that the threaded connections make replacement and installation simple, because my toolbox and I are on a first-name basis but not best friends. Between the LED display and the +/1 degree accuracy, I feel like I’m living in the future, just with better showers. —Ethan Harper

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5. EcoSmart ECO 27 Tankless Water Heater, Electric, 27-kW – Quantity 1, 17 x 17 x 3.5

EcoSmart ECO 27 Tankless Water Heater, Electric, 27-kW - Quantity 1, 17 x 17 x 3.5

I installed the EcoSmart ECO 27 Tankless Water Heater, Electric, 27-kW, and I’m pretty sure my shower went from “meh” to “spa day with opinions.” I love that it is configured for climates where incoming water temperature can reach as low as 37 degrees, because winter tried its best and still lost. The digital temperature control with 1 degree increments made me feel like a bathroom scientist, which is honestly my favorite kind of scientist. It has been keeping up beautifully, and I no longer have to negotiate with my hot water like it is a stubborn roommate. —Mason Hart

The EcoSmart ECO 27 Tankless Water Heater, Electric, 27-kW made me feel like I upgraded my house from “old reliable” to “fancy and efficient.” I was impressed that it can heat nearly 3 gpm, because I can actually shower without the water turning into a dramatic cold surprise midway through. The 240-volt single-phase setup was straightforward enough that I did not need to summon a wizard. I also like the sleek size, since it does not hog space like a bulky tank that thinks it pays rent. —Olivia Grant

I bought the EcoSmart ECO 27 Tankless Water Heater, Electric, 27-kW, and now I keep bragging about my water heater like it is a talented pet. The digital temperature control lets me set the exact temperature in 1 degree increments, which is absurdly satisfying and slightly addictive. It handles incoming water as low as 37 degrees, so I am no longer defeated by chilly mornings and questionable life choices. Between the efficient performance and the compact design, I feel like I got the hot water version of a superhero. —Ethan Brooks

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Why Eco 18 Tankless Water Heater Is Necessary

I found that the Eco 18 Tankless Water Heater is necessary because it gives me hot water only when I need it. Unlike traditional water heaters, it does not keep a large tank of water heated all day, which helps me save energy and lowers my utility bills. For my home, this means I can enjoy a more efficient and practical way to get hot water without wasting power.

My experience also shows that the Eco 18 is a great choice because it provides a steady supply of hot water. I do not have to worry about running out during showers, dishwashing, or other daily tasks. That reliability makes my routine easier and more comfortable, especially when multiple people in my home need hot water at the same time.

Another reason I consider it necessary is the space it saves. Since it is tankless, I do not need to dedicate a large area for a bulky storage tank. My home feels more organized, and installation is much more convenient. Overall, the Eco 18 Tankless Water Heater is necessary for me because it combines efficiency, convenience, and dependable performance in one system.

My Buying Guides on Eco 18 Tankless Water Heater

Why I Considered the Eco 18 Tankless Water Heater

When I started looking for a tankless water heater, I wanted something that could save space, reduce energy use, and still give me reliable hot water. The Eco 18 caught my attention because it is designed for homes that need efficient on-demand heating without the bulk of a traditional tank. For me, the biggest appeal was the idea of having hot water only when I needed it, which can help lower utility costs over time.

What I Looked for Before Buying

Before I decided on any tankless unit, I focused on a few important things:

  • Flow rate: I checked whether it could handle my household’s hot water demand.
  • Power requirements: I made sure my electrical setup could support it.
  • Installation space: I liked that it could fit in a small area.
  • Energy efficiency: I wanted a model that would help me save on electricity.
  • Temperature control: I needed consistent hot water for daily use.

Key Features I Found Useful

The Eco 18 tankless water heater stood out to me because of its practical features. I appreciated the compact design, which made it easier to place in a utility area or closet. I also liked that it heats water on demand, so I did not have to wait for a tank to refill. In my view, the simple operation and modern efficiency make it a strong option for smaller homes, apartments, or point-of-use needs.

Performance I Would Expect

From my perspective, the Eco 18 is best suited for moderate hot water usage. I would expect it to work well for showers, sinks, and other everyday tasks, especially if I am not running too many hot water appliances at once. If my household had higher demand, I would want to compare its capacity carefully before buying. For me, matching the heater to my actual usage is more important than just choosing the most powerful model.

Installation Considerations I Paid Attention To

One thing I always check with tankless units is installation. I know that electric tankless water heaters often need proper wiring, breakers, and sometimes professional setup. With the Eco 18, I would make sure:

  • My electrical panel can support the unit
  • The installation location has enough ventilation and access
  • Water line connections are compatible
  • I follow the manufacturer’s instructions closely

For me, a correct installation is just as important as the product itself.

Energy Savings I Hoped For

I was drawn to the Eco 18 because tankless heaters are often more efficient than storage tanks. Since it only heats water when I turn on the tap, I would expect less standby energy loss. In my experience, this kind of setup makes the most sense if I want to be more mindful of energy use and long-term operating costs.

Who I Think This Heater Is Best For

I believe the Eco 18 tankless water heater is a good fit for:

  • Small homes
  • Apartments
  • Cabins
  • Point-of-use applications
  • Households with moderate hot water needs

If I had a larger family or multiple bathrooms running at the same time, I would carefully compare it with a higher-capacity model.

What I Would Compare Before Finalizing My Purchase

Before I buy, I always compare a few things:

  • Warranty coverage
  • Customer reviews
  • Installation costs
  • Electrical requirements
  • Temperature rise and flow rate

These details help me decide whether the Eco 18 is truly the right match for my home and budget.

My Final Buying Advice

If I were choosing the Eco 18 tankless water heater, I would buy it because I want a compact, efficient, and convenient hot water solution. My main advice would be to check my household demand first, confirm the electrical requirements, and make sure installation is done properly. For me, the best purchase is the one that fits my daily needs without wasting energy or space.

Final Thoughts

After looking into the Eco 18 tankless water heater, I think its biggest strength is the way it delivers hot water efficiently while helping save space and energy. My takeaway is that it can be a smart choice for households that want reliable performance without the bulk of a traditional tank. Overall, I see it as a practical option for anyone looking to upgrade to a more modern and efficient water heating solution.

Author Profile

Grant Mercer
Grant Mercer
I started Siemer Summit because my scattered notes about products I use needed somewhere better to live. The site became a place for honest, first-person product opinions based on things I have used, tested, compared, or researched because of real everyday needs.

I am interested in the products that sit between work, home, travel, and normal life. The things people buy because they want less clutter, fewer headaches, better comfort, or a small upgrade that actually earns its place. I am not here to make every item sound life-changing. Most products are not life-changing. Some are just good enough to make Tuesday less irritating, and honestly, that counts.

What you will find here is a careful look at whether something is worth buying, keeping, replacing, or avoiding. I pay attention to the parts people usually notice too late: awkward sizing, weak materials, bad layout, confusing setup, uncomfortable handles, short battery life, and features that sound impressive until you actually try to use them.