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Availability:
In Stock.
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Friday, Sep 18
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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 gpm
Maximum Temperature: 140 °F
Heat Output: 18 KW
Efficiency: 99.8%
Maximum Pressure: 150
Mount Type: Wall
Capacity: 18 gallons
Item Dimensions W x H: 14.5"W x 18.25"H
Item Weight: 14.8 pounds
Item Depth: 18.25 inches
Color: Gray
Style Name: Whole Home, 18 kw
Brand Name: Rheem
Model Number: RTEX-18
Number of Items: 1
Unit Count: 1 Count
Manufacturer: Rheem
UPC: 020352685335
Global Trade Identification Number: 35
Included Components: Fittings, Aerators
Item Type Name: Water Heater
Manufacturer Part Number: RTEX-18
Material Type: Stainless Steel
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.
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.
Style: Whole Home, 18 kw
a 10+ year old rheem tank needed to be replaced. it wasn't broken but end of service life. and so much so if you drain it. after a lot of research I decided to go with tankless. fearful at first because hey is this truly better? the idea of having on demand seemed appealing. cost savings, of course. but then what type to get?! In the end I settled for a 18k rheem. ecosmart is also well reviewed, but supposedly this is just a rebranded rheem? (like dewalt and black/decker). It is super easy to install. it is small, frees up space, another bonus. costing half of a tank heater. if you can do it yourself... the installation cost is high, as you will have to run new electric and change some plumbing, but that is no biggy. you'll spend about $60 for a valve kit, $50 sharkbites and pex and some for the 8 gauge wire (that can add up if it is a long run btw). for this model you need 2x40amp breakers the water is instantly hot, it easily serves 2 showers, one shower+dishwasher and laundry (tested!) I am very very impressed. also it feels cleaner as there is no water sitting in the tank (you should have seen the drain I had to do from the old tank to get it out of the way). highly recommend a tankless heater and this model works for our household. note: read about technical issues, so far all good, but will update if experienced. installation cost will add up if you can't do it yourself and requires logistics (between plumber and electrician). another installation note: when you get a valve kit with pressure relief (required by most code), it is effectively a gender changer. so when you get flexible hose (female), you need a M/M nipple to attach it to the valve kit... (that is another $20 for 2 nipples to take into consideration). That nipple needs to be taped on the valve attach side, the flex hose side has a o-ring and doesnt need tape (and don't add it either as it will leak)
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Reviewed in the United States on August 7, 2023 by xander
Style: Whole Home, 18 kw
since installing this my wife has had nothing but good things to say about it everytime we bring up having to wait to take a show until the next day or using hot water and not having any for a while, we were limited to 15min of hot water from a 40gallon hot water heater it sucked now we have unlimited hot water and we can get more done why not having to worry if we'll have hot water. DISCLAIMER its will not provide 140F water through 3/4in pipe in winter where i live the water temperatures can be as low as freezing to 42F consistently if it drops below 18F for multiple days. hot sink water, hot shower, but if you want to serve 140F through a 3/4in to 1in line you better have some deep pockets because i think three of these inline would do but then it wouldn't be cost effective, and it would be better to get a whole house unit. I live in a small Trailer and would not recommend for larger house's if you don't also purchase a inline recirculation pump and flow control unit, i don't have one installed now but will be installing the flow control unit. I'm not an HVAC or PLUMBER but if i was I would recommend this product. IF your looking for a gas operated one then i would highly recommend getting it done by a pro, because if you don't install a fresh air vent for a gas one it can use the air in your home leaving it a a reduced rate and possibly if left untreated kill you, electric ones are not as effect but they won't raise your renter insurance or home owners insurances but if you install a gas one you should have a licensee and bonded pro do it because of the implication of doing it wrong could be high, if its in a well ventilated space I'm sure they would still give it its own fresh air because it would run more efficient.
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Reviewed in the United States on January 9, 2024 by Amazon Customer
Style: Whole Home, 18 kw
Do your research. Understand what you are getting. This is not the big tank that sits and keeps water hot all day and night. It only uses energy (electric in this case) when a hot water faucet turns on. I read and read some more and did some research. oh and then did some more! I have installed many tank water heaters but never tankless. This heater requires 2 40 am circuits. In my case my house was only framed out and was easy to install electric requirement. If you are a handyman or high level dIY'er this is easy to install. If not get electrician to do the electric work. (and make sure you have enough AMPS) With many reviews I see people having issues with not enough electricity IE AMPS coming into the house to be able to do an electric water heater. Also know what the water temp is coming into your house. I recommend checking water temp in winter. And check with a thermometer do not believe charts. every place even in same city can be different. Do your research. This heater would not work for house in Chicago in the winter. You would want/need bigger. and is fine for 3 of us with 2 bathrooms. Read instructions and also do some reading online. I found BEFORE I bought it that you should clean it with vinegar every 6 months. Knowing that I installed to make it easy to clean IE flush. Just did my first flush and was piece of cake! (I do wonder if my old tank water heaters in old house would have lasted longer if I had done maintenance on it...even tank water heaters your suppose to clean) I am in central Texas using well water going thru 900 feet of pex pipe buried about a foot. In winter water about 60 degrees summer much warmer. We can shower and run another water faucet easily with temp. set at 120 degrees. we have limiters on all fixtures ie 2.5 gallons per min. on all faucets except bathtub. For bathtub we open faucet about 75% open and fill big 6 foot soaker tub in about 10 min. Bathtub faucets can push out about 7 gallons a minute. Have used it from February thru August and no issues. Would buy again and recommend to friends and family but only if situation IE electrical requirement and water temp were correct for unit.
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Reviewed in the United States on August 26, 2022 by Mike Dunn
Style: Whole Home, 18 kw
I'll leave the original review below. It's been a little over 2+ years and have had to replace every single part and then finally replace the entire unit. Then the new one brand new out of the box did not work properly then finally fail 1yr and 2 months after purchase. This unit should be removed from sale and recalled that is how dangerous they are. If you have this unit installed I would highly recommend take it out and replacing with something else. It almost burned my house down! Just take a look at the pictures in this review and see for yourself. Okay full detail review below. 1st I'd like to say Rheem makes good products but this is not one of them. Here's why: 1st unit failed only less than 1 year of use. The elements exploded inside and needed to be replaced. Fine no problem, kill breaker, shut water off, unscrew 4 wires, take out element replace, re-screw wires, done in 30 minutes. Far beats dealing with a leaking water heater tank with 2 inches of water in your basement. Or lugging a 50lb broken tank up your stairs to replace at the Lowes or Home depot. Ok so I put the new elements in and it's heating again. Not more than a few months later the wire harness started arcing and fused together melting off and almost catching fire. I happened to see the arcing when the unit was on and didn't realize this was not part of how it operates. Thought it was just how it is. It tripped the breaker thankfully. I contacted the company and they sent me a new wire harness. I replaced it, still the unit wouldn't heat. So they sold me new inlet and outlet water sensors and a new flow sensor. That didn't fix it. So they said the motherboard must have fried. So I replaced the motherboard. That didn't fix it. So I purchased a completely new one. I mount the new one hooked it up and the water heater would stop heating randomly during a shower. So I set it to bypass mode 125 degrees and said "heck with the temp controls just give me heat" So a brand new unit I cannot even set the temperature. But I figured 125 is hot enough. Okay moving on. Fast forward to a few days ago, Sept 2nd 2023 brown colored water shot out of my shower head and I knew right away the heater blew. It made 1 year. I open the element rods and sure enough the 1st one exploded worse than any before. Okay no problem, let me swap it with a spare. So I did but.. I had to remove the entire unit from the wall and shake and empty out all the guts that exploded sitting inside the element housing. Still not that hard. So I did it see picture of sink.. EZPZ right? Nope, after repressurizing, a weld must have cracked and a slow drip came down the 1st pipe element housing. I thought maybe its not tight enough. So I tightened it more and the crack go worse and went from a small drip to a full stream. I confirmed it was coming from a welded joint not the threads on the element rod. Okay now the entire unit is trash and needs to be junked all because as I was tightening the element rod it put stress on the joints and cracked them. This is horrible quality in the build and should not happen. So I put the old one back in and swap every part. Wire harnesses, motherboard, elements and finally the sensors. Oh but the sensor's I tightened too much and they broke through the housing which also makes the entire unit useless as that cannot be repaired. So I threaded bolts into their holes and set it to bypass. I ordered a Mizudo instead which does not have copper housings, instead cast aluminum and does not have it's heating rods mixed with the water like this and many unit's have. So far it's been excellent. I highly recommend not purchasing these Rheem electric water heaters for 2 reasons. Fire hazard and quality. They constantly break. Amazon should remove this from their store before someone's house burns down and someone gets hurt or killed. Original Review Below I love this water heater. I really don’t have any complaints. Super easy to install. Takes up like no space. No more water tank to explode damaging my basement. It takes longer to get hot water at the furthest end of the house but it’s so worth it. Once it’s hot it stays hot and I can run a shower plus 2 faucets before I start losing heat. This one took 2 dbl 40amp breakers and it’s powerful enough to heat multiple faucets simultaneously. We never take more than 1 shower at a time anyway with a family of 4. Hasn’t been a problem keeping up with our hot water needs at all. And for the price? This is a great purchase. Ditch the tank! You’ll thank yourself later.
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Reviewed in the United States on January 22, 2021 by F. Digiovanni
Style: Whole Home, 18 kw
These systems are amazing. The future is in your hand when you hold one. I fully recommend. Please, however read on to understand them better. Customer support is awesome and available. This 18kw unit did NOT worked in my home, and I went thru two of the 18kw units before I determined the problem thinking the first one was not working and the problem . Please read on. You will want one and never look back if you read on.. I guarantee You WILL want this one of these water heaters, however, please read on. These WH’s are complicated. They work awesome in the lab environment they were created in. If your home does not match that lab setting or you can’t recreate it. It will not work. I went thru three of them to solve my problem. YOU WILL NEED. Flow restrictions, preasesure regulators, water softener, volt/amp meter filters(?), and a lot of patience tuning it to work. Once tuned however, they are flawlessly perfected at heating water instantly. Wow! the future is in these devices. Why was mine so difficult? I’m the last house from the power company. Literally at the end of the line. And I put in the 18kw unit. They are all super easy to install in both wiring and plumbing, but, what appeared to be my problem was there wasn’t enough physical energy to run it properly. Duel 40 amp req. So it wouldn’t work unless the flow restriction was almost closed. I tweeted and tweeted every possible measure to get it to work. I’m on well water too, so that incoming cold temperature affects the system and set up on a 40/60 pressure switch. The water rate It was moving was to fast and I never could get both sides(heating chambers) of the water heater to come on. It just would NOT work. It would come on for a sink at half open but when you tried to shower. It would turn off and say E5. Oh how I grew to hate that display. A simple to read display and simple to adjust temperature dial. I literally went from Flintstones to The Jetsons in appearance. About the 13kw unit. I had to get instead; WHICH SOLVED MY PROBLEM. It’s a little more than half the power necessary to function. Single 50 amp It is doing its job beautifully now. I have almost full water pressure again and it seems sold at 130 deg. But again, several hours spent tuning so it did work. If the flow rate is to high and water temperature to low it will not work. You have to tune them with additional devices to stabilize them so that units performance in the lab environment it was created in and it needs in your home. I have replaced two tanks now. One electric in a home and one propane in a camper. Worth it! Worth IT! WORTH IT! As for durability; install a water softener or they probably won’t last long without regular maintenance descaling it. I believe fully in this new technology and as well this 18kw unit but if you don’t understand advanced plumbing and advanced electrical troubleshooting if you’re a do-it-yourselfer, hirer someone who is because the electrical power supply will Kill you if you don’t understand it. Let this advice be not a discouraging experience, let it be that your knowledge now of some of the possibilities YOU might encounter moving in the direction of The Jetsons.
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Reviewed in the United States on December 6, 2025 by Biz Trailer
Style: Whole Home, 18 kw
Update: Rheem agreed to warranty the unit and send a new one. Although it was a bit of work to get done, I am thankful to not have to go out and buy a new one. Worked well for a while, but then the thermistor stopped working. It was a pain to get the replacement part I needed, and warranty didn't cover it. When installing the new one, the small partition inside the hole that the thermistor presses against broke, completely bricking the unit. The thermistor then was stuck with water leaking where the wire comes out, and I had to break it to remove it. Poor design. I don't have experience with other tankless heaters, but I would caution against this one for long term usage.
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Reviewed in the United States on June 5, 2026 by A. Moody
Style: Whole Home, 18 kw
Pretty easy to hook up. Don’t be like me, read the instructions well. You need two 2 pole breakers for this heater
Reviewed in the United States on August 10, 2026 by Bria Sissom
Style: Whole Home, 18 kw
Excellent
Reviewed in the United States on July 21, 2026 by GRISELDA