Rheem Marathon Lifetime 50-Gallon Electric Water Heater

The Rheem Marathon Lifetime 50-Gallon Electric Water Heater (MR50245) is the only mainstream residential tank water heater with a non-metallic tank — and the only one that ships with a genuine lifetime warranty against leakage. Where every other tank in this catalog uses glass-lined steel that will eventually corrode and fail (somewhere between year 8 and year 15), the Marathon's seamless polybutylene tank wrapped in fiberglass-filament insulation cannot corrode. There is no anode rod to replace, no sacrificial metal, no tank-bottom rust failure. Buyers who plan to stay in their home for 15+ years repeatedly choose the Marathon for one reason: it's the last water heater they'll ever buy.

Headline specifications

• Capacity: 50 gallons
• Fuel: Electric (dual 4,500W elements)
• Tank material: Polybutylene (non-metallic, seamless, corrosion-proof)
• Insulation: 2.5" fiberglass-filament wrapping the tank
• First Hour Delivery: 62 GPH
• Recovery: 21 GPH at 90°F rise
• Energy Factor (UEF): 0.93
• Warranty: Lifetime non-prorated against tank leakage — limited 6-year on parts
• Anode rod: None required (no metal tank to protect)
• Dimensions: 60" H × 23.75" diameter (wider than steel-tank competitors)

The non-metallic tank advantage

To understand why Marathon owners are evangelical about this unit, it helps to understand how steel-tank water heaters die. The interior of a glass-lined steel tank is exposed to constant chemical attack from dissolved oxygen, chlorides, and varying water chemistry. The glass lining slows that attack but eventually develops microscopic cracks where the steel underneath is exposed. The sacrificial anode rod attracts corrosion to itself (instead of the tank wall), but anodes deplete over 3–5 years and most owners never replace them. Once the anode is gone, corrosion accelerates and the tank starts failing — usually somewhere between year 8 and year 15.

The Marathon has no glass lining because it has no steel tank. The water-contact surface is polybutylene plastic — completely inert to dissolved oxygen and water-chemistry corrosion. There's nothing to corrode, no anode to replace, and no tank-bottom failure mode. The lifetime warranty isn't marketing; it's a statement that Rheem (and previously Rheem Manufacturing under multiple subsidiary brands) has 30+ years of field data on these tanks not failing.

The tradeoff is the form factor: polybutylene tanks are necessarily wider (23.75" vs 22" on steel) and slightly less heat-conductive, requiring slightly thicker insulation. The Marathon is 1.75" wider and a few inches taller than steel-tank competitors. Verify install space before ordering.

Who this model is for

The clearest buyer profile:

• Long-horizon homeowners — anyone planning to stay 15+ years in the home. The Marathon's $1,300–$1,500 upfront price is roughly 2.5× a standard electric tank, but you'll never replace it. Across a 20-year hold, the Marathon costs less than two cycles of standard electric.
• Hard-water homes — corrosion-driven failure is dramatically accelerated by hard water and well water. The Marathon's lifetime warranty isn't voided by water chemistry that would destroy a steel tank in 5–6 years.
• Off-grid and rural installs — where service availability is limited and the cost of an emergency replacement is dramatically higher than in suburban areas. The Marathon eliminates the failure event entirely.
• Risk-averse buyers — the lifetime warranty + zero corrosion mode + no anode maintenance simplifies water-heater ownership to "install and forget."

Where it beats the alternatives

Vs standard 50G electric tank ($499–$599): the Marathon costs $800–$1,000 more upfront. The standard tank fails in year 8–12 and needs full replacement (~$700–$1,200 installed). On a 16-year hold, the Marathon avoids two replacement cycles — economics decisively favor Marathon for long-horizon owners.

Vs Westinghouse Stainless Lifetime 50G Electric ($1,499–$1,699): stainless-steel-tank alternative to the Marathon's polybutylene approach. Similar lifetime warranty, slightly more upfront cost, narrower footprint. Stainless steel is theoretically less inert than polybutylene against some water chemistries — Marathon edges Westinghouse on extreme water-chemistry resilience; Westinghouse edges Marathon on install footprint and conventional aesthetic.

Vs Rheem ProTerra Hybrid Heat Pump 50G ($1,799–$1,999): the ProTerra dominates on operating cost (3.55 UEF vs 0.93). The Marathon dominates on install simplicity (no condensate drain, no ambient air requirement, no cool air output) and tank longevity. For homes without heat-pump install space, Marathon is the right pick. For homes with the space and electrification preference, ProTerra wins.

Vs gas tank ($800–$1,200): gas tanks have lower operating cost in most US regions and faster recovery. The Marathon's value proposition is specific: corrosion-proof tank + lifetime warranty. If you have gas service and no preference for electric, gas remains competitive on lifecycle economics. If you're already on electric and don't have heat-pump install space, Marathon dominates.

Where it falls short

0.93 UEF is standard electric resistance — not bad, but heat pump alternatives at 3.4+ UEF deliver 70% lower running cost. The Marathon's lifecycle math is built on tank longevity, not operating efficiency. If your priority is low utility bills and you have install space for a heat pump, the ProTerra is the better economic choice.

21 GPH recovery rate is class-typical for 4,500W electric — slower than gas. For households with high simultaneous demand (multiple showers, large bathtubs, frequent guests), step up to the 75-gallon or 105-gallon Marathon. Or accept that recovery time after peak demand will be 45–60 minutes.

Wider footprint (23.75") may not fit installs designed for 22" steel tanks. Verify clearance before ordering — particularly in older closet installs and basement utility nooks.

Limited 6-year parts warranty — the lifetime warranty covers the tank itself against leakage, but the heating elements, thermostat, T&P valve, and other parts are covered only for 6 years. These are typically $25–$150 service parts; not a catastrophic failure mode but worth knowing.

Upfront cost is the biggest barrier. $1,299–$1,499 versus $499–$599 for a standard tank. Buyers selling within 5 years won't recover the premium.

Install considerations

Standard electric tank install — no gas, no venting, no condensate drain. Requires a dedicated 30-amp 240V circuit (same as any electric tank).

Verify clearance for the 23.75" diameter and 60" height. The Marathon is wider than typical 50-gallon steel tanks; tight closet installs may need framing modifications.

Installation is simpler than standard tanks because there's no anode rod to position, no glass lining concerns during transport, and the tank itself is dramatically lighter (about 80 lbs vs 160 lbs for steel) — easier for one person to move up basement stairs.

Install cost: $300–$700 in most US markets. The simpler install profile vs steel-tank water heaters slightly reduces labor on average.

Maintenance

The Marathon eliminates most water-heater maintenance:

• No anode rod replacement — there isn't one
• Annual flush still recommended — sediment can still accumulate; the procedure is the same as any tank
• Element replacement when they fail — typically year 8–12 for one element; $30–$80 part, 30-minute DIY replacement
• T&P valve test annually

Beyond annual flushing and element replacement when they eventually fail, Marathon owners report essentially zero maintenance over 15+ year holds.

Bottom line

The Rheem Marathon Lifetime 50-Gallon Electric Water Heater is the right pick for homeowners who plan to stay in the home long-term and want to eliminate the water-heater-replacement event from their future. The non-metallic tank + lifetime warranty against leakage delivers a category of certainty no other residential water heater matches. For buyers selling within 5 years or with install space for a more efficient heat pump, the math favors a different unit. For everyone else — particularly hard-water and well-water homeowners — the Marathon is the install-and-forget answer. Available primarily through Rheem distributors and at Home Depot Pro. Click through to Amazon or your Rheem dealer for live pricing.