I Was Out of Space and Options—Then I Found the Rheem Tankless Water Heater

Until now, I’ve only installed traditional tank-type water heaters, so I didn’t know what to expect from a tankless water heater. But the installation was straightforward, and I’m super happy with the results. 

My husband and I purchased a small commercial building last year, and we’ve been remodeling it on weekends. Because it has no designated utility room,  we’ve had to get creative with our utility setup. After thorough research, we installed the Rheem RTEX-18 Tankless Water Heater. Keep reading to find out more about this space-saving water heater and what I discovered about on-demand hot water heaters in general. 

Rheem RTEX-18 Tankless Water Heater: At a Glance

Our rating: 4.8/5

Testing the Rheem RTEX-18 Tankless Water Heater

To test the RTEX-18, we installed it to meet local codes and the manufacturer’s specifications. Although we are not licensed plumbers or electricians, as general contractors, we have a solid understanding of basic wiring and plumbing. In our community, property owners are permitted to handle their own utility installation. However, DIYers must accurately assess their own skills and follow local codes. Improper installation can cause serious issues, and in many cases, hiring a pro is the safest and most reliable option. 

After installing the unit, we connected it to a sink and noted how quickly the water warmed up. Find out the pros and cons of tankless water heaters and more in my Rheem RTEX-18 review. 

Installation and Space Requirements

I chose to install the RTEX-18 using a manifold system and cross-linked polyethylene tubing (PEX), but you could also use a branch-and-tee system and copper piping. The main thing is to use what meets local code, and to consult a professional if you’re not sure what local code requires. The RTEX-18 arrived with the water heater unit only–the PEX, flexible water inlet and outlet hoses, and manifolds were purchased separately. 

Due to the amount of juice the RTEX-18 pulls when it powers on, we also had to install two 40A double-pole circuit breakers. Rheem’s specs recommended a minimum 150A service panel. We have a 200A panel in the building, so we were good to go. We installed the 40A breakers in the service panel and wired them to the water heater. 

The plumbing involved supplying cold water to the RTEX-18 and connecting the hot water outlet to the hot water manifold. From there, we branched off the manifold to the two sinks in the building. The plumbing and wiring process was straightforward.

I was amazed at how little space was required to install the Rheem tankless water heater. The unit measures 13.9 inches wide, 17 inches high, and is just 3.6 inches deep. I mounted the RTEX-18 to a wall and will eventually install a shallow cabinet to cover it. Compare that with an average of 4 to 6 square feet of floor space required for a tank water heater 5 to 6 feet high. Also, local codes often require additional space around a tank heater for airflow. Practically speaking, there’s no comparison.

Hot Water Delivery Performance

The RTEX-18 starts heating the water as soon as someone turns on a hot water faucet. That flow of water triggers a sensor in the unit, telling it to start heating the water. I was expecting something akin to the amount of time it takes for the tank water heater in my home to deliver hot water but with the Rheem, in just a few seconds, the water coming out of the faucet was nice and hot. 

I was able to select the desired temperature by turning a knob on the front of the RTEX-18. It’s that simple. I experimented with the temperature adjustment and finally settled on 120 degrees F. That was warm enough to wash my hands comfortably. 

However, the RTEX-18 is a relatively small-capacity tankless water heater. If you have a large home with several bathrooms, you may want to consider a higher-capacity model. Rheem offers an interactive tankless sizing tool to help determine the model that will best suit your needs and the geographic location where you live. All in all, the RTEX-18 delivers ample hot water for my needs, and it does it efficiently. 

Cost and Energy Efficiency 

The neat thing about tankless hot water heaters, or on-demand water heaters, is that they don’t need to keep a huge tank of water consistently hot, so they don’t start drawing electricity until someone turns on a hot water faucet. According to Energy.gov, a tankless water heater is 8 to 34 percent more energy efficient than storage water heaters and can save consumers at least $100 annually. The RTEX-18 came with an EnergyGuide sticker that says it will cost an estimated $288 per year to operate. 

The Rheem RTEX-18 tankless water heater sells on Amazon for  $422.61. That price is competitive with similar-sized tankless heaters and maybe a smidgen more than electric storage tank heaters. It’s also a little less, on average, than gas-powered tank heaters. The big savings come over the long term. A tankless hot water heater has an expected lifespan of 20 years or more, while standard tank heaters will last an average of 10-15 years. 

Installation charges will add to the cost of any hot water heater if you’re not experienced in plumbing and wiring. I’m very happy we installed the Rheem tankless water heater in our building. It’s been a couple of weeks, and I haven’t seen a noticeable increase in our electricity usage.

Buy the Rheem tankless water heater on Amazon for $449.00

Product Comparisons

So, is the Rheem tankless water heater right for you?

The Rheem RTEX-18 was the right choice for our building, and now that I’ve installed a tankless water heater, I’m considering upgrading to an on-demand model for my home as well. I live in an area with a rural electric co-op, and the cost per kilowatt hour for electricity is higher than in many regions. I don’t like spending money to keep a whole tank of hot water hot, especially if I’m not using hot water frequently. Plus, the utility area in my building is very small, and the RTEX-18 doesn’t take up much space. To save space for heating and cooling needs, we also installed a Friedrich mini-split heat pump in the building. 

Is an electric tankless water heater right for you? That all depends on your personal needs. If you’re looking to save on energy costs by not having to keep a full tank of water heated 24/7, a tankless model could be a good choice. It’s ideal for lower hot water demands since it doesn’t store hot water. 

On the other hand, if you have a large family or high water usage (multiple showers and appliances), you may need to upgrade to a higher-capacity unit or go with a storage tank type. 

Meet the Tester

Glenda Taylor is a contractor, product tester, and writer focusing primarily on construction, DIY tools, and major appliances.

 

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