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Rheem 18kW 240V Tankless Electric Water Heater

  • Based on 1,704 reviews
Condition: New
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Availability: Only 8 left in stock, order soon!
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Arrives Monday, Apr 22
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Style: Heater


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


Product Dimensions: 14.5"W x 18.25"H


Special Feature: LED Display


Color: Gray


Wattage: 18000 watts


Brand: ‎Rheem


Product Dimensions: ‎14.5"W x 18.25"H


Special Feature: ‎LED Display


Color: ‎Gray


Wattage: ‎18000 watts


Voltage: ‎240 Volts


Maximum Flow Rate: ‎4.4 Gallons Per Minute


Heat Output: ‎18 Kilowatts


Style: ‎Heater


Maximum Operating Pressure: ‎150


Manufacturer: ‎Rheem


Part Number: ‎RTEX-18


Item Weight: ‎14.78 pounds


Item model number: ‎RTEX-18


Is Discontinued By Manufacturer: ‎No


Size: ‎Small


Finish: ‎Stainless Steel


Shape: ‎Rectangle


Installation Method: ‎Wall Mount


Item Package Quantity: ‎1


Water Consumption: ‎7 Gallons


Special Features: ‎LED Display


Usage: ‎Inside; Professional


Included Components: ‎Fittings, Aerators


Batteries Included?: ‎No


Batteries Required?: ‎No


Date First Available: January 19, 2017


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.


  • Works Well
Style: Heater
This unit works very well for my 3 bed/2 bath 1400 sq-ft home. I’ve been running it for a couple of months now to see how well it was going to handle the whole home. Set at 140° it handles two showers at the same time with some hot water to spare for say the bathroom sink if needed. Rarely do we need any extra than the two showers. You do have to be careful when running a tub of water as some faucets can outflow this unit. I have to run our garden tub about 3/4 from wide open so the water stays hot. If your using this for a whole home unit I recommend setting at 140° or 135° but nothing lower. I tried 130° and the two showers were hard to make warm with straight hot going in both. At 140° you can split hot/cold so both get fair amounts of hot water. My only complaint is as other mentioned LED lights will flicker when it kicks on as it takes 75 amps of power to run. I installed this myself with a friend to help run wire, and as long as you know what your doing it’s very easy to wire up. DO NOT ATTEMPT IF YOU HAVE NO ELECTRICAL KNOWLEDGE. Please have it professionally installed if you have any doubts. If you do install yourself make sure and read what size wire it takes as it needs bigger wire than your traditional tank water heaters. Overall I’m very pleased with this unit as we have 5 kids so running the dishwasher, doing laundry, and bathing can use A LOT of water for us and the 50 gal water heater we had just couldn’t keep up. This one is doing great and haven’t noticed any significant water temperature fluctuations other than maybe for the first week which I call a break in period. One shower could get hot then cold several times before getting out. But after the first 4-7 days of usage it leveled out and a hot shower stays hot no matter how long or short it is. Hope this helps anyone looking into these water heaters! ... show more
Reviewed in the United States on April 25, 2021 by Jarod Dunn

  • Less Space and Works Great!
Style: Heater
The system works well in my two bedrooms, one bath home. We recently renovated an older home that we purchased and installed the Rheem 18kw tankless heater in place of the 40-gallon tank system that was there. It’s been only a few months but the system performs well running the washing machine, dishwasher and shower all running at the same time. In addition to heating the water it also takes up much less space than the prior 40-gallon unit it replaced leaving us much greater closet space for other items! I’m glad that we also purchased and installed the HYDRO MASTER Tankless water heater value kit with the unit because it allowed me to easily adjust the water flow into the tankless heater which would initially sometimes show an E5 error message indicating the water flowing through the unit was going too fast to heat the water sufficiently. The value kit allowed me to easily adjust the water flow into the unit as needed which resolved the issue without needing to call a plumber as recommended in the troubleshooting notes. So far so good and I plan to purchase another for my next renovation project. ... show more
Reviewed in the United States on February 10, 2024 by Julian

  • Cost savings in a small box!
Style: Heater
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) ... show more
Reviewed in the United States on August 7, 2023 by xander

  • Easy to install, works well.
Style: Heater
This item arrived slightly damaged, although the packaging was not. I'm not sure if it was a manufacturing or handling issue, but some of the sheet metal frame was bent. I straightened it up with some pliers, as (although not visible once fully installed) it did effect mounting of the cover. Otherwise, the install was fast and straightforward. It does need a ton of amperage to operate (2x dual pole 40 amp breakers), so make sure there's room for them in your panel. The ground is a little "hidden", just a lug on the structure to the left of the opening. Also, I opened up that opening for 1 inch conduit. God help the man that tries to pull 5 #8 wires through 3/4 inch conduit. Get a step drill bit for that, if you're so inclined. After the necessary plumbing and wiring, install took less than an hour. It makes cold water hot, and saves a bunch of space. ... show more
Reviewed in the United States on August 14, 2022 by J. Theren

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