Marathon Water Heaters Review and Buying Tips

Marathon water heaters are unique but simple electric heating appliances with three great features; lifetime warranty, efficient operation, and easy installation.

According to Rheem manufacturer, Marathon is "the most durable electric water heater ever made." Check out the features and benefits that make it one of the preferable products for heating potable water in residential homes.

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Marathon water heaters: Features and advantages

Marathon water heaterMarathon water heater
(photo: amazon)

One of the main advantages, or if I can say the best feature we can see on the Rheem Marathon electric water heaters, is Marathon's lifetime warranty on the water storage tanks.

Lifetime warranty means no tank leaking for as long as you own this unit - no need to buy a heater every 6-10 years due to the corrosion problems. With such a unique design, more savings for you and less garbage into the landfills.

The water storage tank is what makes the Marathon water heater different from others. It is made of the seamless blow-molded polybutene patented as the PermaGuard, and such a tank design eliminates the need for the anode rod, a component part used for corrosion protection. With the absence of the anode rod, smelly water problems or rotten egg smells are eliminated, and less maintenance is involved. Also, such a material ensures lightweight construction, which means inexpensive, easy, and safe installation.

Most of the electric water heaters today, either coming from AO Smith, Bradford White, Kenmore, GE, Rheem, and others, are made of steel and protected by the porcelain enamel and anode rod... still fully unprotected from the corrosive water action.

This is why Marathon electric water heaters are a good buy.

Thick insulation for the high-efficient operation

Marathon heater tanks are insulated with 2.5" thick Envirofoam insulation with a high insulation value of R 20. The 4' pipe insulation is included in the package, so together with the good tank insulation provides higher energy efficiency values and reduced energy loss. Due to its superb insulated tank design, the Marathon manufacturer claims that there is only 5 F of heat loss in 24h through the water tank wall.

The Marathon models are designed with the high energy factor ranging from 0.90 to 0.94 (found only on 30, 40, and 50-gallon models).

Resistant to stress and impact

Outer tough molded tank on Marathon water heaters is made of polyethylene with multiple layers of filament wound fiberglass to increase the durability of the unit so it can withstand higher hot water pressure compared to the standard heaters making it resistant to the dents and scratches.

Professional grade dip tube

A dip tube is commercial-grade with a unique design to provide turbulence in the incoming cold water and at the bottom of the tank to reduce the sediment build-up. The bowl-shaped bottom of the tank allows easier draining and removal of the deposits.

High-performing heating elements

Standard Marathon water heaters are equipped with two stainless steel heating elements; low watt-density coated elements for greater performance, durability, and efficiency. The thermally fused upper element protects against "dry-firing," and the stainless steel Incoloy lower element protects against the lime build-up.

Maximum heating power is 4500 kW on the heating elements, which uses 240 V, while the minimum is 2000 kW found on elements using 120 V.


Rheem Marathon water heaters are mainly built for the whole house and point-of-use residential applications, while some can be used in light commercial applications.

There are several types of Marathon electric models to buy, varying in capacity and size, from the smallest MR15120 as the 15-gallon point of use unit to the largest MR105245. The latest model is a 105-gallon thermal storage tank, designed for alternative water heating applications, such as solar, geothermal, or indirect heating.

It is recommended for large homes with up to 7 members, while popular sizes of 40, 50, and 85 gallons can be used for smaller families.

The most popular "standard" model from Marathon is the 50-gallon model MR50245, tall in size with the height of approximately 62", also available as the short type with the height of approximately 43", which is 5" wider, 5 pounds lighter, has the same recovery but smaller first-hour rating.

Marathon point-of-use models

Marathon point-of-use water heaters (POU) are designed for space-saving and installation in limited spaces. POU heaters utilize the same quality features as the larger ones, but due to their small size and capacity, they are used for point of service applications and are usually installed under the sink, in lavatories, apartments, condos, camps, and restrooms in offices.

The group of point-of-use models comes in two sizes - 15 and 20-gallon. The warranty in residential applications is also lifetime and 6 years on other parts, and if used for light-duty commercial applications, the warranty on tanks changes to 10 years and for other parts only one.

Marathon heavy duty

Marathon heavy-duty electric water heaters are designed for installation in harsh environments and high-temperature applications as they can heat water up to 175 F.

There are two heavy-duty models with the capacities of 85 and 105-gallon, both tall in size. They are also providing a superior design with the upgraded titanium sheath elements used for extreme water conditions.

If you plan to use an alternative energy source, like solar water heating or geothermal, or in combination with the hydronic system, then Marathon "Multi-Port" thermal storage tank is an ideal solution for you. You can choose between three models, standard sizes of 50 gallons, 85, and large 105 tank size.

Heavy-duty Marathon water heaters are equipped with thick insulation to reduce heat loss even more. The multi-port design utilizes the large water connections, conveniently located in front of the unit, and for backup heating, electric heating elements.


Either you are buying a Marathon electric water heater with the standard height, heavy-duty, or point of use, you will not go wrong with selecting this brand. Yes, Rheem Marathon is an expensive water heater, but it provides many excellent features not found on standard type; no tank corrosion, lifetime warranty, lack of anode rod, less maintenance involved, easy draining, and sediment removal, more savings, and less pollution.

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