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Model #RETEX-13

Store SKU #1002624309

Performance 13 kW Self-Modulating 2.54 GPM Tankless Electric Water Heater

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  • Provides continuous hot water for point-of-use applications
  • Small, compact design fits under sinks and in cabinets
  • Water heater requires 1 x 60 AMP double pole breakers
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Product Overview

Help reduce energy usage and save on costs with this Rheem Performance Tankless Electric Point-of-Use Water Heater. The compact design is perfect for installations under a cabinet or sink in your home, office, boat or RV. It requires a 1 x 60 AMP double pole breaker to provide instant, continuous hot water only when needed. Professional installation is recommended. The heater included a 5-year heat exchanger and 1-year parts limited warranty.
  • Energy and cost savings: heats water only when it is needed for savings of up to 50% on water heating costs when used in a point-of-use application
  • Instant, continuous hot water: instantly provides ample hot water for up to 2 showers (review selection guide below to confirm this water heater will provide the hot water needed based on your geographic location)
  • Space savings: small, compact design fits perfectly in tight places like under cabinets and sinks
  • Great investment and value: energy cost savings and a 5-year heat exchanger and 1-year parts limited warranty
  • Easy to adjust: electronic temperature control adjustable in 1-degree increments from 80-140 degrees F with easy-to-read display (Celsius and Fahrenheit compatible)
  • Easy installation: compatible with 1/2 in. water connectors for flex hose installation and no venting or T and P valve required for easy installation (professional installation recommended)
  • Easy to maintain: durable, easy-to-replace heating elements
  • A reliable hot water solution from Rheem, the global leader in water heating
  • Before purchase and installation, please verify that you have the proper electrical requirements for your chosen heater
  • ETL Listed to UL-499 and CAN/CSA-C22.2 No. 64

  • Check out our buying guide on water heaters
  • What tankless water heater is right for you?
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Save $88.01 (20%)
Wattage (watts)13000 W18000 W27000 W24000 W
Application TypeResidentialResidentialResidentialResidential
Number of Showers1-21-21-21-2
Flow Rate @ 45°F Rise (gallons/min)1.97 gal (US)/min2.95 gal (US)/min4.1 gal (US)/min3.64 gal (US)/min
Water Heater FeaturesWall MountedOverheat Protection,Wall MountedWall MountedWall Mounted
Fuel TypeElectricElectricElectricElectric
Efficiency Level Super High
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Product Depth (in.)
3.625 in
Product Height (in.)
12 in
Product Width (in.)
8.25 in
Water Connection Size (in.)
1/2 in NPT adapter included


Amperage (amps)
57 A
Application Type
Electricity Phase
Single Phase
Finish Family
Flow Rate @ 35°F Rise (gallons/min)
2.54 gal (US)/min
Flow Rate @ 45°F Rise (gallons/min)
1.97 gal (US)/min
Flow Rate @ 55°F Rise (gallons/min)
1.61 gal (US)/min
Flow Rate @ 65°F Rise (gallons/min)
1.37 gal (US)/min
Fuel Type
Heat Exchanger Warranty
5 Year
Maximum Temperature (F)
140 °F
Minimum Activation Rate (gpm)
Minimum Temperature (F)
80 °F
Number of Elements
Number of Showers
Pack Size
Product Weight (lb.)
7 lb
Required Volt Connection
240 volt
Uniform Energy Factor
Water Heater Features
Wall Mounted
Wattage (watts)
13000 W

Warranty / Certifications

Certifications and Listings
CSA Listed,ETL Listed,UL Listed
Labor Warranty
No Warranty
Part Warranty
1 Year

Questions & Answers

Typical questions asked about products:

  • Is the product durable?
  • Is the product easy to use?
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Customer Reviews

  • 4.2
    out of 1,436 reviews
  • 73%recommend this product
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Showing 1-10 of 1,436 reviews
Easy to install, great product and work for a house...
Easy to install, great product and work for a house with 3 bathroom i don't have any complaints
    2 people found this helpful
    It was very easy to ensamble...
    It was very easy to ensamble
      excellent product, very nice
      • Verified Purchase
      2 people found this helpful
      So far, so good. I recently purchased the 11kw model to replace a 20 gallon tank electric water h...
      So far, so good. I recently purchased the 11kw model to replace a 20 gallon tank electric water heater that serves (an added on) bathroom with a stand-up shower only. It is now installed under the sink. I was already used to conserving my hot water in this particular shower so I already use a 1.2 gpm low flow showerhead with shutoff/flow lever (available at HD). I'm keeping the low flow set up since I think it'll help ensure that this tankless water heater is able to heat my incoming water and operate most efficiently. My incoming water is from a backyard well (SW Oregon) and it is pretty cold, so far this water heater delivers very adequate hot water and flow for me with the unit set at 115 degrees. Unless you're very knowledgeable, definitely hire an electrician for the wiring upgrades. My meter/service panel happens to be just on the outside of this bathroom wall, so the new wiring run was fairly easy. Don't skimp, get new high amp wiring and new high amp breakers installed as recommended by the manufacturer and you should be fine. The only thing I would consider before buying and converting to tankless is...how much hot water do you need?...and how many fixtures are served? Study what is available carefully and consult a plumbing/electrical contractor before tearing anything out first. I'm happy with the product and my results here.
      • DIY
      • Recommended
      8 people found this helpful
      Easy installation, instant hot water.
      We live in a 2700 Square feet home in Florida with 4 bedrooms & 3.5 baths. We have your typical dishwasher and washing machine. We purchased the 27KW unit for our entire house. The installation was easy and instructions straight forward. The unit is able to heat the water through the entire house, even while 2 are showering and the dishwasher is running. Overall, we are very satisfied with this unit.
        • Recommended
        20 people found this helpful
        Choose the correct size and yes you can recirculate for instant
        So I studied over this tankless idea for a few weeks and here is some of my research/thoughts. 1. Test your inlet water temperature. 2. Take a 5 gallon bucket to each fixture and gauge how many GPM each fixture puts out in a minute. 3. Look at your electrical panel. This 27KW requires 3/40a double pole breakers and 3/8-2 runs of Romex. Minimum requirement is a 200amp main breaker. 4. If you have some electrical knowledge you can very easily hook this up electrically and easily shark bite/Pex the plumbing. 5. I can run 2 showers wide open hot @3.5gpm with 56.5* inlet temp and still have 1/3 of the final element left for more. 6. I just finished installing a water recirculation pump at heater and bridge valves under master bath sink and kitchen sink. I installed the pump on a smart switch which I have automated in our house. I have the pump on slowest setting. I plugged pump into a smart plug at tank. I have a smart outlet that plugs in at kitchen sink. You can turn that switch on at kitchen sink and it activates the tank smart plug to kick the water pump on. The bridge valves allow cold water in hot water lines to flow into cold water lines until the bridge closes internally (Meaning water is hot at bridge). Also have smart activation in master bathroom. No more wasting water waiting on it to heat up. When water pump is activated in any automation it’s set to turn off after 2 minutes per Smart Things App. BOKYWOX Hot Water Circulation Pump 3/4'',3-Speed Circulating Pump (RS15-6SB) This is the stainless model. Grundfos 595926 Bridge valves So now I have endless hot water and now instant endless. At .3gpm the flow meter activated first element. Hope this helps someone.
          • Recommended
          62 people found this helpful
          Must Have
          Installed this heater 3 months ago but wanted to evaluate performance etc before reviewing. Being a retired plumber I did install myself including adding breakers to panel and pulling wires. This unit requires 200 amp service and 3 40amp 2 pole breakers. Make sure your panel meets requirements and has available slots in panel. I left the original water heater breaker in but turned it off and disconnected wires. If you have a very good working knowledge of plumbing and electric you can do this install. Allow 1 day to do/run electrical work and 1 day to install heater. There will be some piping that will need to be reworked in order to make good clean connections to heater. Living in AZ we don't generally have extremely cold weather. Right now water temp into the heater is about 50 degrees and the Retex27 heats it to 110 degrees with no problem which is the temp I have set it for. 110 degree water is barely tolerable and not get scalded. Make sure to install a service valve kit as tankless heaters require cleaning of the heating elements. Cleaning elements is a simple process, just takes some time. I've seen some reviews say their lights dim when it turns on. I have not had that issue. Having a teen daughter it is nice not having to wait for a tank heater to recharge and she likes being able to stand under the hot water longer! Another myth with tankless heaters is it is instant hot water. Not true, it is endless hot water. You still have to wait for the cold water in the pipes to flow through and the hot water to arrive just like a tank heater. Another bit of info, the ECO27 is the same as the Retex27. The ECO27 has a lifetime warranty and Retex27 is 5 years. I did not have the luxury of waiting 2 weeks for the ECO27 to arrive as my old heater was leaking. If my research is correct Ecosmart manufactures tankless heaters for Rheem and parts are universal. Bottom line, I reccomend either of these heaters and tankless is the way to go.
            • Recommended
            71 people found this helpful
            Endless Hot Water
            I love this small tankless water heater. I had some leaks at the threaded connections but resolved that with Rector T plus 2. The reason I haven’t given this product a 5 is the temperature control is acting flaky. Turning the dial doesn’t change the temp. I wiggle the knob and it will change a few degrees then stop again. I called Rheem for a warranty claim. They were excellent, and are sending a replacement main board. The only problem I have with the design is that you have to dismount the unit to remove screws to take off the front cover. That could be easily fixed. I finally got the temp up to 105 degree setting and took a shower. The hot water was great! BTW I installed this in our RV on a 50 amp feed.
              • Recommended
              11 people found this helpful
              Recommended but installation is difficult
              Just finished installation. Unless you are very comfortable with plumbing mods and electrical installation, factor in a professional electrician and/or plumber to the cost of this unit. This unit (18Kw) requires two separate double 40 amp breakers since the unit draws 75 amps. My old tank water heater had one double breaker and I had no available slots in the breaker box, so I disconnected a hot tub that wasn't used much (I'll go back and add a box for that later). The most difficult part was that the manufacturer required 8 gauge wire for both circuits and my old unit used 10 gauge. I had 6 gauge laying around so I used that but I would have been better off going to HD and buying 8 gauge since the 6 was a bear to work with and requires huge conduit (see pic) - the wire I used also had an outer insulation with added to the size. Do yourself a favor and research "wire ampacity" so you can correctly calculate the wire gauge based on the distance from the breakers to the water heater. Distance makes a big difference in choosing the correct wire gauge. Since my circuit was only 20', I probably could have used smaller wire. This heater is working well so far (2 days) and heats as fast as my old tank, but I live on hot Florida where the water comes out of the tap at 78 degrees.
                • Recommended
                23 people found this helpful
                Great Unit BUT Think through The Installation Before You Buy Your Parts!
                The unit (Rheem RETEX 13) itself is excellent! My installation took 7-8 hours longer than it should have because 2 separate Home Depots' "experts" sold me the wrong parts. They both tried real hard but they made it harder than it really is. With the right parts a DIY install should only take 3-4 hours and it isn't hard at all. Parts you'll need: a 60 Amp double pole breaker, 6/2 wire, (plus I recommend a cut off box), PVC conduit, a water purifier (makes your unit last longer), 2 pieces of 1/2" female thread to sharkbite flex hose (the ones you use for a sink) with shut off valves (for servicing your unit), 1/2" CPVC, a 1/2"elbow, 2 pieces adapter 3/4" male thread to 1/2" CPVC (for purifier), and whatever adapters you need to tie into your water in and out pipes. Tools you'll need; a flat head screwdriver (for connecting the wires), a small phillips head (for the unit's cover), level (make sure the input hose is level), wire cutters, PVC cleaner and glue (HD sells a kit with both), 2 pairs of pliers or open ended wrenches (to connect the flex hoses to the unit and the adapters to the purifier), a screw gun (to mount the unit and the cut off box), some pipe clamps (I recommend clamping your pipes to the wall, a handfull of screws, plumbers tape, and plumbers paste. Before you decide to buy one of these make sure your panel has enough power coming in to accommodate the unit. Install; (Turn off water main and main breaker before starting) I started by running my wire from the panel area to my garage where it was to be installed. Next I took the 2 small screws that hold the cover on, then used the included template and mounted the unit to the wall. I put a screw part way in above the top of the unit so it would not slide up and off the screws while I worked on it. Next I chose a spot for my cut off box and mounted it to the wall. (Do NOT install this below the unit.) Next I installed a 12" long 1/2 female flex hose with built in valve and sharkbite end to the water in and out on the unit. On the hot side (left) I connected a piece of 1/2" CPVC with a 1/2 to 3/4 adapter on it, then glued that piece to the 3/4 hot pipe that runs to my 2 showers, garden tub, 2 bathroom sinks, kitchen sink, washing machine, and utility sink. On the cold side I connected the already installed flex hose to a piece of 1/2" CPVC. On the purifier I had already installed a male threaded 3/4" to 1/2" converter on the in and out so I glued the 1/2" pipe to the output. From the purifier input I ran another piece of 1/2" CPVC to a 90 degree elbow, then another piece of 1/2" CPVC down to a 1/2" to 3/4" converter attached to my cold water in pipe. After allowing 3 hours (yeah overkill) for the glue to dry I turned the water main back on and water tested the unit until I was satisfied there were no leaks. Next I ran a piece of the 6/2 wire from the cut off box to the unit, then connected the wire from the panel to the cut off box. Back inside the house at the panel I removed the 30 Amp breaker from my old water heater. I connected the new wire to my 60 Amp breaker and installed it into the panel. Before turning the power back on I turned on the hot water on a nearby sink and let it run for a few minutes. It is VERY IMPORTANT to get the air out of the line. With the water still running I threw the main breaker, then the water heater breaker. No sparks, no smoke, everything looked OK. Then I went back to the garage, held in the button to turn on the unit, set it at 130 degrees, and went back inside. It took (and takes) about 1 minute for the heated water to reach the sink but once it does it goes from warm to hot very quickly. With everything up and running I re-installed the unit's cover. I have been using this for 2 weeks now with no issues. After failing to install with the parts that HD originally sold me I did call Rheem's customer service to verify the install I had in my mind would work. They were very helpful! The quotes I got to have a professional plumber and electrician do my install were insane. I'm all for paying a fair wage but paying someone's mortgage and car payment for 1-2 hours work just didn't fit the program. This is NOT a hard job, I would give it a 4 out of 10 difficulty. *I used a few more pieces that what I described because I had to keep piecing it together with the wrong parts
                  • Recommended
                  56 people found this helpful
                  Showing 1-10 of 1,436 reviews