Rheem Marathon Electric Water Heater Review: Pros, Cons & Is It Worth It?

Last Revised: 3/20/25 

Running out of hot water unexpectedly or dealing with a leaking water heater can turn an ordinary day into a major hassle. Whether it’s cold showers, rising energy bills, or leaks and flooding, an outdated water heater can cause serious problems. 

At Mattioni, we’ve been helping homeowners navigate these issues for over 75 years, specializing in finding the best, longest-lasting solutions – like the Rheem Marathon. 

The Rheem Marathon electric water heater is on the short list of options for anyone looking for an efficient,  reliable, and long-lasting upgrade. Known for its durability, energy efficiency, and rust-proof design, the Marathon has built a reputation as one of the best investments for homeowners. But is it right for you? 

In this article, we’ll break down the key benefits, drawbacks, and cost considerations so you can confidently determine if the Rheem Marathon is the right fit for your home. Let’s start by exploring how it earned its name – its longevity. 

7 Key Benefits of the Rheem Marathon to Know 

1. The Longest Lifespan Available 

Most traditional water heaters last 10-15 years before they start to rust, leak, or fail. Tankless models can last a few more years, averaging 15-18 years of operational life. And then there’s the Rheem Marathon.  

The Rheem Marathon’s plastic tank is built to last for decades, which sounds too good to be true – until you see its lifetime warranty. This level of warranty coverage is incredibly rare and serves as a testament to Rheem’s confidence in its durability. The unit has a seamless, blow-molded polybutene inner tank that is highly resistant to rust and corrosion. It also has a filament-wound fiberglass outer shell, which resists dents, scratches, and airborne contaminants. 

What does that mean for you? It’s marketed as the last water heater you’ll ever need to buy for your home. While that may only be true in rare cases, it can be expected to at least double the operational lifespan of the average tank-type water heater. So long as it’s properly maintained, the Rheem Marathon should cruise through its first 20 years of life, and in many cases can reach at least 30 years. When compared to other options, this longevity is vastly superior. 

2. High-End Energy Efficiency and Lower Energy Bills 

The energy efficiency of your water heater is one of the most critical factors as it’ll determine your utility costs for years into the future. Your water heater alone makes up about 20% of your monthly bill, according to Georgia Power. When it comes to keeping your bill low, the Rheem Marathon is close to the top of the list, with a UEF (Uniform Energy Factor) up to .92 – due in large part to its superior insulation rating.   

Traditional water heaters have UEFs that range as low as .63 and as high as .95. The only type of water heater that truly outclasses the Rheem Marathon is an electric hybrid (heat pump) water heater, which can have a UEF of over 4.0. 

All tank-type water heaters experience “standby losses,” which equates to the additional energy required to keep water hot after it has already been heated. Marathon water heaters experience standby losses of only 5% over 24 hours. In other words, if your water heater is set to 120°F and you lose power, after 24 hours it will only be 6°F cooler. You can see how the strong insulation of Rheem Marathon water heaters significantly reduces “standby” heat losses, and makes them among the most efficient across the marketplace. 

3. Rust & Leak-Proof Tank Design 

The seamless, blow-molded polybutene inner tank is good for more than just prolonged system longevity – it’s also rustproof and corrosion-resistant, giving you peace of mind that even a small leak will never occur. Moreover, the plastic tank also prevents water contamination which can occur as a traditional tank corrodes and rusts.  

With a traditional steel tank water heater, you must pay close attention to its condition as it ages to avoid major system failure and contamination from corrosion and rust. With a Rheem Marathon, you can rest assured that these issues don’t pose a threat to its plastic tank. 

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Its plastic tank makes the Rheem Marathon a standout option from a longevity perspective, and its superior insulation and efficiency rating puts it in the conversation with tankless and hybrid models. 

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4. High-Tech Feature Integration 

There’s a lot more to the Marathon water heater than its plastic tank – several integrated features help support its efficiency and longevity. It’s got an advanced circuitry system called Dry Fire Protection, which ensures that the heating elements only turn on when fully submerged by water. In addition to being a safety feature, Dry Fire Protection supports energy efficiency and a prolonged lifespan. 

It’s also equipped with Automatic Temperature Control, which continually optimizes hot water performance and energy efficiency so that it only uses energy when needed. This feature is possible because of its minimal standby losses and superior insulation (made up of the environmentally friendly material Envirofoam).  

The Marathon also has a tough outer jacket and can withstand any accidental bumps without bruising. It’s a strong and modern piece of equipment from the inside out. 

Click here to learn more about the Marathon’s system features 

5. Environmentally Friendly 

The Rheem Marathon is more than an efficient, durable, and reliable water heater – its top-of-the-line energy efficiency also makes it the environmentally responsible choice. When you upgrade from a traditional water heater to the Marathon, you’ll reduce your carbon footprint as well as your utility bills. It’s a win-win for both your wallet and the planet. 

6. Excellent Lifetime Warranty on the Tank 

If you’re still unsure about the longevity of the Marathon’s plastic tank, look no further than the manufacturer’s warranties for assurance. Rheem is so confident in the quality of the seamless, blow-molded polybutene inner tank that it includes a lifetime warranty on the tank. This level of coverage is rarely found in any product, clearly displaying the reliability of the Marathon’s plastic tank. With this water heater, you’ll have lasting peace of mind. 

7. Reliable Performance and Comfort 

Perhaps most significant of all is the reliability of the Rheem Marathon. It consistently delivers hot water, ensuring you always have it when you need it. Plus, it’s available in a wide range of sizes, from 15 to 105 gallons, making it a great choice for any home. 

4 Potential Drawbacks of the Rheem Marathon to Consider 

Even though there are extensive benefits to choosing the Rheem Marathon as your home’s next water heater, it’s still wise to evaluate it for its potential drawbacks before making your final decision. Here are a few things to keep in mind before making your decision: 

1. Potentially Higher Upfront Cost 

It’s important to understand how the Rheem Marathon’s price tag stacks up against other types of water heaters available. While it comes at a lower cost than most tankless and heat pump water heaters, it’s more expensive than standard steel tank water heaters. However, its long lifespan and energy savings will help offset the higher installation costs. 

2. Specialized Components may be Expensive During Repairs 

The tank is covered with a lifetime warranty, but other components (like specialized heating elements and thermostats) aren’t. Sooner or later, these specialized parts will need some attention to keep the system functioning. If they fail, replacements can be more expensive than standard water heater parts. 

Before making a final decision, make sure that you understand while the plastic tank carries a lifetime warranty, other components of a Rheem Marathon water heater don’t. Nevertheless, with proper maintenance, this system should last longer than any other. 

Learn how a VIP membership with Mattioni can maximize your water heater’s lifespan. 

3. Slower Hot Water Recovery Times 

The Marathon is electric, not gas, so it takes longer to heat water than a propane or natural gas model. Its recovery performance is listed at 21 Gallons per Hour (GPH), whereas the typical gas water heater is in the range of 40-60 GPH.  

If you match your tank size to the number of household occupants, this may rarely ever impact your family. But if you ever have several guests visiting or you’ve installed a tank that’s too small, you may run out of hot water and have to wait for it to replenish.  

4. Bulkier Footprint than Standard Tank Models 

Even though it’s lighter than most other tank-type water heaters, it’s a bit bulkier – 21 5/8” in diameter. If you have a tight installation space, double-check your measurements before purchasing. If you’re unsure if you’ll have enough space to install a Rheem Marathon water heater in your home, consulting with a professional plumber is always advisable. 

Is the Rheem Marathon the Right Fit for You? 

If you’re looking for a durable, energy-efficient, and rust-proof water heater that won’t leave you with surprise leaks or fail prematurely, the Rheem Marathon is absolutely worth it. Its plastic tank makes it a standout option from a longevity perspective, and its superior insulation and efficiency rating puts it in the conversation with tankless and hybrid models.  

If you’re planning on moving soon, or don’t have the short-term budget, then installing the Rheem Marathon might not make the most sense for you. Additionally, be sure you have the space for its footprint and select a tank size that matches your home’s water demands before selecting a model.  If you want a water heater that has the potential to last 20+ years, take a close look at the Rheem Marathon water heater. 

But here’s the thing – the right water heater is only as good as its installation. At Mattioni, our expert team will help you find the perfect fit for your home, so you never have to worry about running out of hot water again. 

We handle everything from removal of your current water heater to installation so you can stay focused on your life, not installing your water heater. For over 75 years, we’ve backed all our work with a simple promise: Service Guaranteed to go Swimmingly. 

Whenever you’re ready to get started with your next water heater, call our friendly team at (610) 400-8510 or schedule your consultation online. Take the first steps toward securing your home’s comfort today!