Marathon Water Heaters Reviews – 2022 Guide

| Last Updated: July 1, 2021

Are you searching for an excellent Marathon water heater?

You don’t need to worry at all. You can go through this article to find out the best Marathon water heater.

These need a very large storage space that can fulfill the needs of a large family and commercial areas. They are energy efficient and made with high insulation materials. So, select a heater from our list and buy one for yourself.

Disclaimer: To avoid any confusion, please understand the names Marathon and Rheem are used interchangeably. Rheem is the company who makes Marathon water heaters.

How Does Rheem Compare to the Competition?

Rheem wins the competition of water heaters because of its outstanding and excellent features. Let us have a look at some of its specifications.

Resistant to Corrosion

The outer surface of a Marathon tank is made up of polyethylene. This coating prevents the surface from getting scratches, dents, and reactions due to salty air. It has several layers of filament-wound fiberglass that helps in increasing the durability and strength of the water heater. Plus, it can bear a higher pressure of hot water than standard water heaters.

High-Quality Heating Elements

There are two types of heating elements; low-watt, density-coated elements and thermally-fused elements. Low-watt density elements are famous for excellent performance, strength, and high efficiency. Thermally fused components are useful for protecting the tank against dry-firing. The stainless steel body prevents lime formation. The highest heating power for such heaters is 4500 kW, and the lowest heating power is 2000 kW.

Easy to Install

Marathon heaters are lightweight, which makes them easy to move and use. The tank bottom is like a bowl. This helps drain the leftovers, for example, residue and sediment from the water heater. The waterproof grommets protect the water in the tank from condensation.

Comparison of the Best Rheem Marathon Water Heaters

We are listing the best Marathon water heaters present in the market. You need to know every single detail before buying any product. So to help you to find the best Marathon heater, here’s a quick comparison of the best ones. 

Model Name


Unit Size (Gallons)


Energy Efficiency


Cost of Unit Only




 0.90 – 0.94 EF



15 – 20

2000W and 3000W at 120 Volts and 240 Volts




0.92 EF




0.90 – 0.94 EF




0.90 – 0.92 UEF




0.92 EF




0.93 EF


Review of the Best Rheem Marathon Water Heaters

Finding a Marathon water heater is not easy at all. You need to know everything before purchasing it. We have listed the best Rheem Marathon water heaters along with their detailed reviews. Choose one for yourself by looking over all the factors.

Best Overall

Rheem MR50245 Marathon

No products found.


Max Water Flow (GPM): N/A

Energy Factor (EF): N/A

Dimensions: 23.5 (diameter) x 62.8

Water Temp Range: N/A

No products found. On Amazon

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Why it Stands Out to Us

This Marathon heater stands out to us because of its excellent performance. It has a drain valve made of brass for full flow. It is very different from standard heaters. It does not corrode or rust like other traditional heaters.

The tank is made up of polybutene. It is simple to use and install. It is also durable, reliable, and light in weight. You can learn the installation method easily by reading the instruction manual. Customers are very happy with the results of this Marathon heater. This is one of the best available in the market.

Bottom Line

Summing it up, you will never regret buying this heater. It has amazing qualities and specifications. It is not at all difficult to use or install. It has amazing features like polyurethane insulation, a polybutene tank, and brass drain valves.

It consumes very little energy and power, and won’t increase the electricity bill. Moreover, it is rust-free and corrosion-free. You don’t need to waste time and money buying or installing the anode rods. Plus, it is resistant to dry firing and leakage. Also, it is successful in gaining customer’s satisfaction.


Reliable and very easy to install

No need to have an anode rod for this heater

Seamless polybutene tank, which prevents it from rusting and corroding

Thermally-fused parts (upper elements) that protect the heater from dry firing

Contains insulation of polyurethane, which reduces the consumption of energy


It is taller than other Marathon heaters

The thermostat stops working after a few days

After about 2 years, you need to replace the elements


Rheem MR20120 Marathon


Max Water Flow (GPM): N/A

Energy Factor (EF): N/A

Dimensions: 23 3/4 (diameter) x 34 1/2

Water Temp Range: N/A

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Why it Stands Out to Us

This Marathon heater is great because its features are quite impressive. It can hold 15 or 20 gallons of water. It has a 2000-watt and 3000-watt elements at 120 volts and 240 volts. Water tightening grommets prevent overhead humidity and condensation.

Meanwhile, the tank bottom is similar to a bowl that drains the sediment from the heater completely. You can easily maneuver or position the tank due to its low weight. It is useful and helpful for different applications. It minimizes power utilization and heat loss. It is also durable, strong, rust-resistant, and energy-efficient.

Bottom Line

Wrapping it up, this non-metallic electric heater is one of the fastest-selling products. You can use it where fitting a large heater is not possible. It is useful for small places like apartments, cabins, offices, restrooms in commercial buildings, and recreational property. Moreover, it contains a lot of protective coatings.

The polyethylene shell protects the tank from scratches, dents, and salty air. The water grommets protect the water from condensing. The thermally-fused parts provide protection against dry-firing, which extends the life of the tank. It also has a pressure valve and a temperature relief valve. It helps control the pressure and temperature of the tank.


No need for anode rods due to the plastic tank

Has a bowl-type tank bottom that helps in draining the sediment completely

Pro3Different layers of fiberglass (filament-wound) increases the strength of the tankPro3

Outer shell is made up of tough polyethylene that prevents salt air, dents, and scratches

Avoids loss due to the standby heat and energy utilization due to insulation of polyurethane


Limited lifetime warranty

Best for the Money

Marathon 30-Gallon MR30245C


Max Water Flow (GPM): N/A

Energy Factor (EF): N/A

Dimensions: 22 (diameter) x 54.50

Water Temp Range: N/A

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Why it Stands Out to Us

This electric Marathon heater is available at a relatively affordable price. It will provide you with hot water according to your needs. It saves maximum energy through the pipe wrap, making it energy-efficient. It has a round bottom that drains all of the residue from the tank.

It avoids lime formation due to the titanium lower base. It stands out to us because it is pocket-friendly and gives optimal performance. It has five different holding capacities. The efficiency of this heater is 0.90-0.92 UE, which is very impressive.

Bottom Line

This electric Marathon heater is one of the most durable, strong heaters available in the market. Every single penny you will spend on it is worth it. You will never regret buying it. It has great quality and specifications. It is light in weight and compact in size, thus, you can move or carry it anywhere.

You can use it in your home or office. It has an LLW primary warranty and a dip tube of polysulfone. It is resistant to humidity, corrosion, rusting, and damp conditions. So if you are looking for a Marathon heater, you must get your hands on this one.


Tank bottom helps in draining the sediment and residue

Provides hot water within a few seconds and is affordable, too

Lower element is made up of titanium that prevents the formation of lime

Polyethylene coating prevents the outer shell from damages and scratches

Includes an energy-saving kit (pipe wrap) that helps get the maximum power savings


Lower elements blow out very quickly

The leakage stops sometimes, but it starts again

You need to replace the heating element frequently

Best Marathon 50-Gallon Water Heater

Marathon 50-Gallon MSR50245C


Max Water Flow (GPM): N/A

Energy Factor (EF): N/A

Dimensions: 28.3 (diameter) x 47.3

Water Temp Range: N/A

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Why it Stands Out to Us

This Marathon heater is the best 50-gallon heater for us because it can hold enough hot water to fulfill the basic needs of your house. You can use it in industries and farmhouses, as well. It is very safe to use because it provides 100 percent safety to the user.

Its outer surface remains the same in all types of weather conditions. Moreover, it is famous for its high-quality performance and excellent exterior design. It provides maximum efficiency due to the foam insulation that covers the whole tank.

Bottom Line

In conclusion, this electric Marathon heater is worth buying. You will never regret buying it. You don’t need an anode rod for heating the water. The packaging of this heater includes an easy to read and understand instruction manual.

You just need to follow the instructions. There’s no need to call for professional help to install this lightweight heater. The plastic tank prevents the water from getting a bad smell. It has different capacities for holding hot water. Its efficiency is 0.93 EF, which is a perfect requirement. It does not consume a lot of energy for heating the water.


Lightweight and has a beautiful design

You can install and use it without any difficulty

The whole tank has firm foam insulation that provides maximum efficiency

Plastic tank prevents the need for anode rod and production of smelly water

Prevents corrosion, rusting, and oxidation with the polybutene and polyethylene coating


It is quite tall

The thermostat has some defects

Replacement of elements may cause a burden on your pocket

Best Marathon 80-Gallon Water Heater

Marathon 85-Gallon MRG85245C


Max Water Flow (GPM): N/A

Energy Factor (EF): N/A

Dimensions: 28.25 (diameter) x 70.25

Water Temp Range: N/A

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Why it Stands Out to Us

This is the best 80-gallon water heater available in the market. The display panel is present at the top, which means it is not at all a danger to children. You can use it in your home or factory. Industries that use hot water in their product-making process can also use it for immediate heating. It has a very large storage space, which can fulfill the needs of a big family. It has a pre-installed temperature and pressure controlling valve. Other green hybrid models are more expensive than this unit.

Bottom Line

This is a hybrid water heater. It is unobtrusive and consumes very little energy. Thus, you don’t need to worry about your utility bills. If you have a large family of five or more members, then you need a large electric water heater. This heater is perfect for your big family. You can also use it in a hostel where people are sharing rooms. It further comes with a warranty of 15 years to provide you with ease of mind.


Includes a pressure valve, temperature valve, and an energy-saving kit

Can heat and store a large amount of hot water due to its great capacity

Display panel is at the top, thus, no one will be able to disturb your settings

Has a sleek polyurethane structure that will help you to reduce your water heating bill


A bit pricey

Improper heating thermostat and elements

Plastic tank leaks some chemicals in the water after using it a few times

Best Marathon 105-Gallon Water Heater

Marathon 100-Gallon MRG105245C


Max Water Flow (GPM): 0.90

Energy Factor (EF): N/A

Dimensions: 30.25 (diameter) x 70.75

Water Temp Range: N/A

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Why it Stands Out to Us

The amazing features and high-quality performance of this heater are the reasons for which we are discussing it. It aims to provide customers with maximum protection and 100 percent of results. You can use this high-capacity heater in your industries and factories.

Hostels and hotels can also use it so that visitors can have a soothing and relaxing hot shower or bath. It is made using strong materials and insulation. It is highly efficient, which means it uses very little energy and gives excellent performance. If you are living in a chilly area, then you must give it a try.

Bottom Line

Wrapping it up, this Marathon heater provides a very large capacity for heating and storing hot water. You can use it for commercial and big residential areas. It is worth buying. It deserves your attention and appreciation.

People already using it are very happy and glad by its result. This is one of the most popular and durable water heaters available in the marketplace. Every single penny is worth spending. It is also very safe to use and easy to install. It does not require any anode or professional help for installment.


Avoids moisture forming at the overhead of the tank

Includes insulation of 4’ that provides maximum savings

You can save on your electricity bill because they consume very little energy

Contains the latest pre-installed factory for the vacuum relief valve, which makes it easy to install

Lower elements provide great resistance to avoid any damage occurring due to the formation of lime


The inner elements are not strong enough

Does not work properly at different places

You should replace the heater once a month

Best Marathon Electric Water Heater

Marathon 40-Gallon MR40245C


Max Water Flow (GPM): 0.92

Energy Factor (EF): N/A

Dimensions: 21.8 (diameter) x 65.5

Water Temp Range: N/A

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Why it Stands Out to Us

This electric heater stands out to us because of its astounding performance. You can use it in small residential areas. It provides enough hot water for taking multiple showers at a time and has spectacular specifications. It is successful in gaining the customer’s trust and loyalty. It is environment-friendly and does not produce any CFC or HCFC gas that can harm the ozone layer, people, nature, and animals. This is because it has EnviroFoam insulation. With this, you can solve many of your problems regarding water heating.

Bottom Line

In a nutshell, this heater is perfect for a family that has three to four members. You can get hot water within a few minutes. There’s no need to waste time and energy. This is one of the most durable heaters. It minimizes the requirement of power and energy and is suitable for different purposes.

Plus, it is strong enough to withstand high pressures. It contains a lot of safety measures, a protective coating, and helpful functions. Through this, you can set your requirements. The company provides the maximum possible warranty to purchasers. You should buy this product without thinking too much.


Produces less pollution, which can cause harm to the environment

Uses very little energy and power due to the energy-saving mechanism

All the wiring is present in a conduit that helps in controlling the wiring with no difficulty

Dip tube made up of polysulfone helps transfer cold water at the bottom of the plastic tank

Filament wound of fiberglass provides more flexibility and bears more water pressure than the standard heaters


Costlier than standard units

Tank starts to leak after a few months

Plastic tank releases some chemicals in the water and needs frequent replacement

What Kind of Warranty Does Rheem Offer?

The main thing customers consider before buying any product is the warranty given by the company. They don’t like to burden on their pockets after purchasing an expensive product. The company offers maximum feasibility through its warranty, which automatically catches the attention of people. Rheem aims to provide its customers with maximum comfort and ease even after purchasing their products.

Limited Warranty

Rheem offers its customers a limited time warranty on some of its heaters. This warranty is for a given period of time. It is not responsible for faults out of control of Rheem and the flaws in material or workmanship that are not at all linked with the company. 

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6-Year Warranty

Rheem provides its customers with a warranty for six years that starts from the day you have bought the heater. This warranty remains valid only as long the original purchaser remains in the same house where the heater was installed. This six-year warranty is for parts and tanks, and also includes a one-year warranty for labor.

Replacement Policy

Rheem cares about its customers a lot. It promises to replace the whole heater if the tank leaks within the warranty period. It will replace any defective part within nine years due to faulty materials or poor workmanship. This warranty has a three-year free service period. 

Who is Rheem?

Rheem is a private American company that has its headquarters in Atlanta, Georgia. The names of the owners of this company are Richard Rheem, Donald Rheem, and Edwin Ruud. The company works on plumbing, cooling, and heating applications. The products are accessible in South America, North America, the Middle East, and Australia. 

In 1941, the company won the title of the largest manufacturer of water heaters in the United States. The main products of this company include air conditioners, household furnaces, and water heaters.

rheem logo


To put it simply, Marathon heaters are worth buying. They are quite different from standard heaters. You can buy them according to your budget and needs. They have strong insulation, which prevents them from a lot of defects and problems. We are sure the performance of these heaters will never disappoint you. 

People Also Ask

You need to clear all your confusion and misunderstandings before buying any Marathon water heater. There might still be a few questions in your mind. You should know the answers to every single question. To clear out your misunderstandings, we are answering a few of the frequently asked questions.

What is a Marathon Water Heater?

Marathon heaters are also known as Rheem water heaters. They are the most durable and strong water heaters available in the market. The inner tank is made up of plastic. This plastic tank prevents the heater from corroding and rusting. It also consists of a 2.5-inch insulation of polyurethane for minimizing heat loss and saving energy.

Are Marathon Water Heaters Worth the Money?

When comparing Marathon water heaters with traditional heaters, they are a bit expensive but are still are worth buying. They have outstanding features and quality and are resistant to corrosion. They have a warranty for a lifetime. Marathon heaters do not require any anode rod. They are very easy to install and maintain. They consume less energy and create less pollution. You can easily remove the sediment and other contaminants from these heaters. Thus, they are definitely worth the money.

My name is Bob Wells and I am a retired HVAC tech from Washington state. I am currently retired and no longer do much with HVAC, however, I feel like I have a lot of knowledge in the subject and I wanted to create a website where I could talk about what I've learned and help upcoming HVAC techs. Find more info about me and HVAC Training 101.