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Marathon 105 Gallon Water Heater

Availability: In stock

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Quick Overview

MR105245 Electric Water Heater


The Rheem Marathon water heater, MR105245, has a capacity of 105 gallons. Rheem Marathon’s sizing guide for electric water heaters recommends the MR10545 for large households with 7 or more people. The MR105245 Marathon water heater is the best electric water heater in the size category for 100 gallon water heaters. The MR105245 is commonly used for conventional water heating, thermal water storage, as well as demand response programs. Rheem Marathon water heaters make an excellent product choice due to their highly efficient design, light weight, and durability.

Marathon water heaters do not rust or corrode. They are made of polybutene making them impervious to harsh water conditions. Rust and corrosion is the cause of many water heater leaks in conventional electric water heaters made of steel. Rheem Marathon water heaters are built with quality. Marathon water heaters are backed by a residential limited lifetime warranty. Other electric water heaters may only carry a 6-12 year warranty.

Marathon water heaters are non-metallic water heaters made of cross-fiber polybutene. This advanced design results in a higher quality and stronger electric water heater that lasts much longer than steel tank electric water heaters. The Marathon water heater comes equipped with two electric heating elements:

  • Upper electric water heater element. The upper factory furnished Rheem Marathon water heater element is made of copper, fused to protect against dry firing, and has an electric rating of 4500 watts.
  • Lower electric water heater element. The lower factory installed Rheem Marathon water heater element is made of titanium, non-fused, with an electric rating of 4500 watts. The titanium plated element provides additional protection against lime and sediment build up.

The 105 gallon Marathon water heater is a great replacement for many 100 gallon water heaters. Please be aware that GP Conservation also stocks a slightly smaller 85 gallon Rheem Marathon water heater which could also be considered when replacing 100 gallon water heaters.


  • Seamless, blow-molded, polybutene tank impervious to rust and corrosion.
  • Multiple layers of filament wound fiberglass to give tank extra strength.
  • A recessed drain valve so it's out of the way of brooms and scrubbers.
  • Tough molded polyethylene outer shell to resist against dents and scratches.
  • High temperature polysulfone dip tube.
  • Factory installed conduit between element control boxes.
  • All plastic tank eliminating the need for an anode rod.
  • Manufactured in America.

Energy Savings

Rheem Marathon water heaters (MR105245) are unrivaled for their energy savings. Rheem Marathon water heaters are an energy efficient water heater choice for your home. The Polyurethane Envirofoam insulation surrounding the water heater tank is superior to insulation in other electric water heaters. The Envirofoam insulation reduces heat losses by trapping the heat inside the tank and keeping the water hot for longer periods of time. As a result, the water heater elements do not need to turn on and off very often to re-heat the water. Rheem Marathon water heaters use electric immersion water heater elements which transfer 100% of their energy into heating the water.

Standard electric water heaters typically suffer from high standby losses: Up to 20% of the energy used in standard electric water heaters is to compensate for heat loss. Stand-by losses are much lower in Marathon electric water heaters amounting to 5% or less per 24-hour period. Home owners can often save energy by replacing a 100 gallon water heater with an energy efficient Rheem Marathon water heater.


Capacity: 105 Gallons
Element Size: 4500 Watts (240 Volts)
Tank Height: 66 3/4 Inches
Height to Top of Connections: 70 3/4 Inches
Tank Diameter: 30 1/4 Inches
Weight: 152 lbs
Standards: Meets or exceeds ANSI standard and is UL listed. 
Energy Factor:

All units come complete with factory installed temperature and pressure relief valve, replaceable brass drain valve, and vacuum relief valve. The connections for cold inlet and hot outlet are 3/4 inch NTP, and should be roughed in at 5 3/4 inches on center.


Rheem Marathon water heaters come with a residential limited lifetime tank warranty as long as you own your home. If the home is sold, the warranty transfers to 15 years from the date of installation and the next owner receives coverage for the time remaining. All elements and parts are warranted for 6 years from manufacture date against factory defects.

Additional Information

SKU MR105245
Manufacturer Rheem
Energy Source Electric
Tank Size (gal) 105
Certifications None
First Hour Rating (gal) 100+