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Rule of thumb
The 135 rule: repair or replace a water heater
The short answer
The “135 rule” is an informal name people use for the water-heater repair-or-replace decision. It is not a codified industry standard, but what it points to is real: replace rather than repair when the fix would cost more than about half a new unit, or when the heater is past roughly a decade old. Below are the two rules plumbers and manufacturers actually cite, so you can make the call with real numbers.
A note on the name
You may have searched for “the 135 rule” and found a lot of hand-waving. We looked, and it is not a named rule in manufacturer or trade literature the way, say, building codes are. It circulates as shorthand. Rather than invent a definition, here is the guidance reputable sources do publish, which is what the shorthand is reaching for.
The 50 percent rule
The most widely cited version: if a repair would cost more than half the price of a new water heater installed, replace it instead. Manufacturers including Rheem and A.O. Smith publish versions of this guidance. The logic is simple. Sinking $800 into a heater that is near the end of its life, when a new one is $1,500, rarely pays off.
Sources: Rheem, when to repair vs. replace, A.O. Smith, repair or replace.
The age-times-$100 formula
A second rule of thumb folds in the unit’s age. Add the repair cost to the age in years multiplied by $100. If the total is more than the cost of a new unit, replace. A $400 repair on an 8-year-old heater works out to $400 plus $800, or $1,200, so if a new unit costs less than that, replacement wins. It is a fast gut check, not a precise calculation.
Age thresholds on their own
Many plumbers also use age as a standalone signal. Under about 8 years with a modest repair, lean toward fixing it. Over 10 years, lean toward replacement regardless, because failures tend to cluster near the end of a tank’s life. A conventional tank generally lasts 8 to 12 years.
Put it together
Get the repair quote, check the age, and compare against the cost of a new unit installed from our water heater replacement cost guide. And remember the one clear-cut case: a leak from the tank body itself cannot be repaired, so a tank leak means replacement no matter what the formulas say.
Common questions
Repair-or-replace questions
What is the 135 rule for plumbing?
The “135 rule” is an informal name some homeowners and forums use for the repair-or-replace decision on a water heater, not a codified industry standard. What people mean by it lines up with two rules plumbers and manufacturers actually cite: replace if a repair would cost more than about half the price of a new unit, and lean toward replacement once the heater is past roughly a decade old.
What is the 50 percent rule for a water heater?
If the cost to repair your water heater is more than 50 percent of the cost of a new one installed, most guidance says replace it rather than repair. Manufacturers including Rheem and A.O. Smith publish versions of this rule. For example, if a new unit is $1,500 installed and the repair quote is $750 or more, replacement is usually the better value.
How old should a water heater be before you replace it?
A conventional tank water heater generally lasts 8 to 12 years. Many plumbers lean toward repair on a unit under about 8 years old if the fix is modest, and toward replacement once it is past 10, especially if it is also leaking or has failed before. Age is a factor to weigh alongside repair cost, not a hard cutoff.
Is there a formula that combines age and repair cost?
Yes. One rule of thumb adds the repair cost to the unit’s age in years times $100, and says replace if that total exceeds the cost of a new unit. For a $400 repair on an 8-year-old heater, that is $400 plus $800, or $1,200; if a new unit costs less than that, replace. It is a quick sanity check, not a precise rule.
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How to get an honest price
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