Tank water heaters last about 8 to 12 years, sometimes longer when the anode rod was actually replaced and the water is kind. The average one in a listing was installed by the previous owner and forgotten. Tankless units last longer and fail differently: scale, a failed heat exchanger, or a vent that was never correct. Either way, the listing will not tell you the year. The serial number will.

A failed tank is one of the most common insured water losses in houses, and it is also one of the most preventable capital items to just replace before it dumps forty gallons into a finished floor.

What it is

A storage tank, gas or electric, or a tankless gas unit on the wall. Age is in the serial number. Manufacturers publish the decoding. The anode rod is the sacrificial metal that delays tank rust. Almost nobody replaces it, which is why the "12-year warranty" tank dies at year 9. Temperature and pressure relief valves that dump into the room, missing drip pans, and missing expansion tanks are the code and insurance issues sitting next to age.

Gas units need a flue that drafts. A gas water heater and a furnace sharing a sloppy vent is a classic combination when someone replaces one and not the other. See old HVAC if both are original.

How to spot it in the listing

Utility closet and garage photos. A rusty bottom, a pan full of water, scorch marks, or a unit sitting directly on a wood garage floor without a pan are visible. "New water heater" should say the year. If the interior was renovated and the mechanicals were not photographed, assume they were not renovated. That is a flip tell as much as a plumbing tell.

How to spot it at the showing

Photograph the label. Note gas or electric, capacity, and any manufacture date. Look at the floor around it. White crust or a rust ring is past leakage. Look at the TPR discharge. It should run to a safe place, typically within inches of the floor or to a drain, not capped, not uphill. For tankless, ask about maintenance descaling. A unit in a hard-water town that has never been flushed is a scaled unit. Run the hot water. A long wait and a rumble are an aging tank, not proof of failure. Lukewarm water at every fixture can be a failed dip tube or an undersized tankless.

The real risk

The tank rusts through and releases stored water, usually at the bottom, often while you are not home. The damage is the floor, the ceiling below, and the mold if it sits. The heater itself is the cheap part. Tankless units rarely dump a tank of water. They fail by not heating, or by leaking at fittings. A backdrafting gas flue is the safety risk, and it belongs to a combustion test, not a glance.

Insurance and lending

Carriers pay for sudden rupture more often than they pay for slow seepage, and they are increasingly asking the age of the water heater. Some will require replacement above a stated age, or they exclude water damage from an old tank. Ask before you waive. A 15-year-old tank in a finished basement over a hardwood first floor is an underwriting question, not a trivia question. Lenders rarely care if the house has hot water. Appraisers notice an active leak. FHA can require a leaking heater to be repaired. A quiet old tank closes, and then it is yours.

Typical cost ranges

Typical ranges, not quotes.

Standard tank replacement, gas or electric, 40 to 50 gallons, accessible: commonly $1,200 to $2,500 installed, more if the flue, pan, or expansion tank has to be brought up with it.
Same job in a tight closet, a tall flue change, or a relocation: often $2,500 to $4,500.
Tankless gas replacement or new install: commonly $3,000 to $6,000, higher when the gas line or vent has to be enlarged. The upsizing is the surprise, not the box on the wall.
Expansion tank, pan, and TPR corrections at the same time: a few hundred dollars. Do them with the replacement, not as a second trip.

A seller who "just replaced it" should have the permit and the receipt. An unpermitted gas connection is not a gift.

Pass, negotiate, or investigate

Investigate by reading the serial number on any house you are serious about. It takes five minutes. Negotiate when the tank is past about 12 years, already leaking, or the insurer wants it replaced as a condition of the policy. The typical range is small enough that a credit is cleaner than a seller rushing a unit in before closing. Pass is almost never about the water heater alone. Pass when it is one of several deferred machines (furnace, roof, panel) and the price assumes a renovated house. Put the serial number on the inspection checklist. If the inspector does not photograph the label, ask them to go back.

Water Heater Age: The Serial Number, the Pan, and the Leak Waiting