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Rheem

Rheem 18kW 240V Tankless Electric Water Heater, Gray

  • Based on 2,521 reviews
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Style: Whole Home, 18 kw


Features

  • External digital thermostatic control with LED display (+/1 degree accuracy)
  • Most advanced self-modulation, adjust power to meet hot water demand
  • Durable Copper immersion two heating elements, field Serviceable. Flow Rate- up to 4.4 GPM
  • Simple installation bottom 3/4 inch NPT water connections
  • Threaded for easy replacement, simple installation, digital temperature display

Description

This tankless electric water heater is ideal for mid-range whole-home applications. This unit is ideal for single shower applications in the Midwest. The Rheem Performance tankless electric water heaters offer a continuous, endless supply of hot water. A lower kilowatt unit can provide hot water on demand for single or multiple point-of-use applications while a higher kilowatt unit could provide hot water for a whole house depending on the inlet ground water temperature. Tankless electric water heaters save space, save energy, save money, and require no venting. The sleek, compact size, 90 percent smaller than a tank, allows you to save space and place the unit wherever you want, including under a sink. Tankless units only draw energy when hot water is flowing, while traditional tanks are constantly drawing energy to keep the water in the tank at the desired temperature. Rheem's self-modulating technology can save Up to 50 percent on your water heating bill.

Brand: Rheem


Capacity: 18 Gallons


Power Source: AC Power


Product Dimensions: 14.5"W x 18.25"H


Special Feature: LED Display


Power Source: AC Power


Special Features: LED Display


Wattage: 18000 watts


Voltage: 240 Volts


Flow Rate: 4.4 Gallons Per Minute


Maximum Temperature: 140 Degrees Fahrenheit


Heat Output: 18 Kilowatts


Efficiency: 99.8%


Maximum Pressure: 150


Mount Type: Wall


Is Electric: Yes


Color: Gray


Style Name: Whole Home, 18 kw


Material Type: Stainless Steel


Capacity: 18 Gallons


Item Dimensions W x H: 14.5"W x 18.25"H


Item Weight: 14.78 Pounds


Item Depth: 18.25 inches


Brand Name: Rheem


Model Number: RTEX-18


Manufacturer: Rheem


UPC: 020352685335


Global Trade Identification Number: 35


Manufacturer Part Number: RTEX-18


Included Components: Fittings, Aerators


Unit Count: 1.0 Count


Item Type Name: Water Heater


Frequently asked questions

The Rheem 18kW 240V tankless electric water heater can provide a maximum flow rate of up to 4.4 gallons per minute at a 35°F temperature rise. The flow rate may vary depending on your home's incoming water temperature.

This tankless water heater requires 240V electrical connection, and it's recommended to be installed by a professional. It's designed for easy replacement of your existing water heater and it comes with a digital temperature control in 1-degree increments for complete control of hot water.

Yes, the Rheem 18kW tankless water heater is highly energy efficient. It's designed to heat water only when it's needed, eliminating the need for a storage tank and reducing energy consumption.

Yes, this product comes with a 5-year warranty for heating chamber and 1-year warranty for parts. Please register the product to activate the warranty.

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Top Amazon Reviews

🚀 Abunda's Overview

This is our summary and key points to consider based on customer reviews.

The Rheem Tankless Water Heater was generally well received, with users particularly praising its compact design and nearly instant hot water supply. Noteworthy also were its energy-saving qualities and the fact that it never runs out of hot water. Some users, however, expressed concerns about installation difficulties and sufficient hot water supply for simultaneous multiple use (such as two showers at once). A few users also mentioned some confusion regarding the unit's wiring, and one cautioned that the unit might not work as effectively for filling bathtubs. As a whole though, most reviewers found the product to be well worth the purchase.

Pros

  • 👍 Compact design frees up space
  • 💰 Significant energy saver
  • 🔥 Provides nearly instant hot water
  • 💧 Unlimited hot water supply

Cons

  • 👎 Difficulty with self-installation; may require a professional
  • 🛠 Some confusion around the wiring
  • 🚿 May not provide sufficient hot water for multiple simultaneous uses
  • 🛁 Might not supply enough hot water for filling bathtubs

Should I Buy It?

If you are looking for a compact, energy-efficient solution for your hot water needs, and do not mind possibly hiring professionals for installation, then yes, the Rheem Tankless Water Heater is a sound purchase. However, if you have a larger household or often require multiple simultaneous uses of hot water, you might want to consider a larger model.

    • Easy installation. Works well.
Style: Whole Home, 24 kw
Review Image by K.Barron
Just installed. Works well. Hope it will last longer than the off brand one we had before. Very easy installation due to being a replacement for the same style unit. Electrical, plumbing and mounting locations all the same.
Reviewed in the United States on March 29, 2026 by K.Barron
    • Easy install
Style: Whole Home, 24 kw
Great quality
Reviewed in the United States on April 8, 2026 by Emily
    • Tankless Hot Water install
Style: Whole Home, 24 kw
I replaced a 55 gallon hot water tank with this unit, I bought a little larger unit than what the ratings said I needed to be safe. Make sure you check your electrical panel to make sure you have room for 3 x 40 double pole 40 amp circuit breakers. I didn’t have enough room, had to add a sub panel plus had to run 9 x 8 gauge wires the unit requires. I’m pretty handy, but asked a certified electrician to help me with the pre wiring. To be honest, I would have been afraid to try and do this myself even with all my experience. Installation was pretty simple after you have the wiring installed. Use 1 inch piping from your electrical panel to the tankless electrical unit or you won’t be able to pull the nine 8 gauge wires through the pipe. I also suggest having an electrical panel with a main breaker so you don’t have to shut the whole house down for the final install. Additionally i installed a surge protector to hopefully protect the unit from power surges which appears to have delicate electronics inside. We’ve only had this unit in operation for 4 days so far, but the water is really hot, have had no issues at this point and I love the added space gained without having the tank. Time will tell if we save 50% on energy, but from all my research it makes sense even with us living in a warm climate. There are several tankless unit manufacturers with great ratings, I went with Rheem because if I have an issue, they are based in the USA and hopefully that means English speaking in my time zone….. Hope my review is helpful to you. Update: it’s been 7 months, still works great, very happy with this decision even though I can say I’ve seen significant energy savings ... show more
Reviewed in the United States on May 6, 2025 by Amazon Customer
    • Hot Garbage
Style: Whole Home, 18 kw
New Review: Ok, this lasted 26 months before I finally ripped it off the wall and replaced it. It had failed three times in that 26 months, and this was the last straw for me. After almost exactly one year, one of the heating elements fell apart. It was literally in pieces. I replaced the bad element with a third-party element, and almost exactly one year later, the second factory heating element fell apart, too. My water has very low mineral content, but after the first one failed, I cleaned the elements every six months along with flushing the whole system. That still didn’t keep the factory elements from failing. The third-party elements looked fine. I bought some spares just in case. Finally, last weekend I started noticing that the water coming out of the tap was CRAZY hot. When I started looking for the problem, I found that one of the heating elements was stuck on all of the time. The water would just keep heating up inside until the thermal protection circuit turned it off. Something in the electronics had failed. There was another issue with the water heater unrelated to these failures, too. I have solar panels on my roof, and I found that whenever someone would turn on the hot water, the solar inverter would turn off. The water heater was injecting too much electrical noise onto my power lines, which the inverter didn’t like. There is absolutely zero electrical noise filtering on the water heater, so I added my own. This fixed the solar problem, but the filter that I added consumed some power all of the time, so it wasn’t saving me energy like I’d wanted. I replaced it earlier this week with a 24kW model from a different manufacturer thar I found locally. The new one, even though it has a higher power rating, uses nearly half of the energy required by the Rheem to take a shower, 7kW vs 12kW. Since it has a higher power rating, it’s easier to use hot water at multiple points simultaneously. It also has a dynamically adjusting flow meter, compared to the Rheem where I needed to add an external flow restrictor. Don’t buy this heater. Spend a few dollars more and get something that is built better, doesn’t constantly break down, and doesn’t cost as much to operate. Get a Stiebel Eltron Tempra 24 Plus, which costs a bit more up front, but works much, much better. Original Review: A week shy of one year ago, I purchased this to replace the old water heater in my home that had quit working. The installation was easy, it only took me an hour or so to swap out, and it worked great. For a year. My warranty will expire in three days, and the water heater stopped working a few days ago. It wasn’t completely dead, and it would heat the water to around 85 degrees, but that still makes a miserable shower. I called the warranty department, and they sent me a troubleshooting guide. Using this guide, I determined that one of the heating elements was open. Honestly, I didn’t feel like it was worth the effort of trying to get this fixed under warranty, so I ordered a replacement (two, so I could replace them both) 9kW heating element here on Amazon and they were delivered the next day. The maintenance instructions say that you should pull the elements out every 6-12 months and soak them in vinegar to remove any scale, but admittedly, I hadn’t done that. My water is very soft with a low mineral count, so I tend to neglect things like this. When I removed the bad element, there were no mineral or calcium deposits on it, but the element was in horrible shape. It was all burned up, with gaping holes, twisted metal, and exposed, broken metal coils. The other element looked perfect. The bad one looked like it had been in a furnace. I replaced the elements with new ones, and it’s operational again. I’m happy with this heater while it is working, but I don’t know if I’m crazy about possibly needing to replace the elements once a year. Hopefully, I just had bad luck with the one element. ... show more
Reviewed in the United States on March 20, 2022 by ES

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