Marathon Water Heaters

The Marathon electric water heater offers these advantages:

  • Technologically advanced design is clearly differentiated from short lived steel water heaters.
  • It’s the most durable water heater made, with a warranty to match.
  • Tank comes complete with a factory installed vacuum relief valve and temperature pressure relief valve.
  • Replaceable brass drain valve.
  • Seamless blow molded polyethylene tank with no anode rod required for a corrosion free life.
  • High temperature, commercial-grade diptubes for greater durability.
  • The filament wound fiberglass outer tank is designed to be more flexible and withstand more pressure than conventional tanks.
  • Our unique high temperature dip tube is offset from the concave bottom, creating a “whirlpool effect” which helps prevent sediment build-up.


How much more is the Marathon than a conventional water heater?
The residential Marathon units will cost approximately 2 to 3 times more than a basic steel water heater. That is not a real comparison though, as you are comparing a lifetime warranty product against a 5 or 6 year warranty product. Installation for the Marathon is no more and sometimes less than for steel units.

Commercial units such as the 75, 85 and 105 gallon models are attractively priced. Our manufacturing process is technologically advanced and very efficient so our incremental cost between our smaller tanks and our larger ones is much smaller than that of steel tanks.

Is it worth more than a conventional water heater?
Yes. The Marathon after a few years won’t have to be replaced. The cost of the water heater is usually only half your cost however. Installation is the other cost and you won’t have to pay for that and another water heater time after time. The other thing people often overlook is the damage to their floor and belongings when their cheaper water heater fails.

Why should I bother, my last water heater lasted 22 years?
That’s impressive but not uncommon for older water heaters. Older water heaters had much thicker steel and more porcelain than today’s units. Because manufacturers have cut so many costs from the manufacturing process, most steel water heaters made today will not last much longer than their warranty.

What if I’m not a CPI customer, can I still purchase a Marathon?

Yes. If you live in the area you may purchase a Marathon from our Philomath office location. If you are outside of the area and would like one shipped to your area you may do so by purchasing it from their online retailer at .

What size water heater should I buy?
The first limitation is the heaters physical size and the space available for installation. If space is not an issue you can use this guide to help determine your peak hour demand which is the key to sizing your water heater.


All units come complete with a factory installed temperature and pressure relief valve, replaceable brass drain valve, and vacuum relief valve. (*Light Duty Commercial)

Capacity (gallons)
 Diameter x Height
Tank Weight
MR30245 30 4500 W 21 5/8″ x 49 1/2″ 75 lbs
MR40245 40 4500 W 21 5/8″ x 65 1/2″ 90 lbs
MR50245 50 4500 W 23 1/2″ x 66 3/4″ 100 lbs
MSR50245 50 Short 4500 W 28 1/4″ x 47 1/4″ 95 lbs
MHD75245* 75 4500 W 28 1/4″ x 62 5/8″ 122 lbs
MHD85245* 85 4500 W 28 1/4″ x 70 1/4″ 134 lbs
MHD105245* 105 4500 W 30 1/4″ x 70 3/4″ 152 lbs


  • Other element configurations are available for most models
  • Height is measured to the top of the T&P valve
  • Shipping weight is approximately 6 to 10 pounds greater than tank weight for all units

Residential Warranty

Marathon offers this no-leak promise because of its superior, non-metallic PermaGuard tank construction – a seamless blow molded polybutylene tank with a filament wound fiberglass outer tank for maximum strength. Superior performance, high-efficiency, and low operating cost…for a lifetime*!

(*10 year warranty is upgraded for free after a simple online registration. Please see your owner’s manual for more information.)

Agricultural and Business Warranty

When you buy a Marathon water heater for these demanding applications, you are buying long term efficiency and peace-of-mind. Whether you are dealing with the high moisture and demand of agricultural applications, temperature extremes of commercial sites, or the multiple installations of a lease program, the Marathon is the long distance performer. With a proven track record in these environments, Marathon water heaters installed in these applications are warranted not to leak for a period of 5 years*

Parts Warranty

Component parts of the Marathon water heater such as the thermostats and elements are warranted for a period of six years from date of manufacture for all residential applications after a simple online registration, and of one year from date of installation for agricultural applications.

Installation Tips

  • Your Marathon tank is one of the lightest available. There is no need for special equipment or the Olympic Weight Lifting Team to get your Marathon installed.
  • Unlike regular tanks, the Marathon can be shipped or moved on its side. Our super strong shell is unaffected by shipping on its side even over hundreds of miles!
  • Do not solder directly against the tank! Solder your first connection and then attach it to the tank unions.
  • Be sure to properly vent the water heater by opening a hot water faucet until only water comes out before energizing the elements.
  • Flushing water mains, broken water mains, and many other water system operations can create extreme vacuums within your plumbing system. Your Marathon comes complete with a vacuum relief valve which must remain installed to protect your tank and system.

Maintenance tips

  • In areas of hard water, better performance will be realized by using lower wattage elements. We encourage the use of 3800 watt or lower wattage elements in these applications.
  • If you have sediment in your water, Marathon’s unique “bowl shape” bottom will allow you to efficiently and easily drain the tank and sediment. Typically drawing off five gallons of water a couple of times of year will flush out the sediment.
  • If you encounter severe sediment build-up, the Marathon element ports are oversized to allow a wet/dry vacuum hose to be introduced to clean out sediment. Be sure to turn off power and follow all safety precautions.
  • Paint, ink, and indelible markers may be easily removed from the polyethylene jacket of the Marathon by using vandalism/stain removers.

Marathon Current Pricing

Model Number Gallon Price
MR30245 30 $879.00
MR40245 40 $889.00
MR50245 50 $929.00
MRS50245 50 $1,039.00
MHD75245* 75 $1,229.00
MHD85245* 85 $1,329.00
MHD105245* 105 $1,479.00

* Light Duty Commercial