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Marathon 40 Gallon Water Heater


Quick Overview

MR40245 Electric Water Heater
SKU: MR40245


The MR40245 Rheem Marathon water heater features a high efficiency design and a lightweight tank that does not corrode. Each Marathon water heater comes with a limited lifetime warranty against water heater leaks.

Rheem Marathon water heaters are made of cross-fiber polybutene, so unlike a metal tank, hard water cannot damage the water heater tank. As a result Marathon water heaters last much longer than standard steel electric water heaters.

Rheem Marathon water heater tanks, built free of metal, eliminate the need for sacrificial anode rods. Marathon water heaters are often used to replace water heaters with sacrificial anodes that can cause a sulfuric odor. 

The 40 gallon water heater is appropriate for installations in homes with 2-3 family members. 


  • 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

All Rheem Marathon water heaters use immersion electric water heater elements which apply 100% of the energy they use towards heating water stored in the tank. . Rheem Marathon water heaters experience very little heat losses due to high-tech Envirofoam insulation that surrounds the water heater tank. The Envirofoam insulation traps the heat inside the tank and keeps the water hotter for longer periods of time without the water heater’s elements cycling on and off to re-heat the water.

Standard electric water heaters suffer from high standby losses; up to 20% of the energy used in old standard electric water heaters is used to make up for heat losses. Rheem Marathon water heaters have standby losses of 5% or less per 24 hours. Replacing a standard electric water heater with a Rheem Marathon water heater can result in significant energy savings.


Capacity: 40 gallons
Element Size: 4500 Watts (240 Volts)
Tank Height: 61 1/2
Height to Top of Connections: 65 1/2 Inches
Tank Diameter: 21 3/4 Inches
Weight: 90 lbs
Standards: Meets or exceeds ANSI standard and is UL listed. 
Energy Factor:

All Marathon water heaters 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.


Rheem Marathon water heaters (MR and MTS models) used in single family dwellings come with a lifetime tank warranty as long as you own your home. If the home is sold, the warranty transfers to a 10 year warranty from the date of the original installation. The next owner receives warranty coverage for the time remaining. All elements and parts are warranted for 6 years from manufacturing date against factory defects.

Units must be registered within 90 days of installation to qualify for Rheem's Limited Lifetime Warranty. 

Additional Information

Manufacturer Rheem
Energy Source Electric
Tank Size (gal) 40
Certifications None
First Hour Rating 50 - 59

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