Water heaters: read the serial plate, then look at the rod
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Three companies build the tank water heaters sold in America under a dozen different names, and a single sacrificial rod decides how long any of them lasts. This page decodes the serial plate of all three makers and lists what the rod costs against what a new heater costs.
Flexible magnesium anode rod, 42 inch, 3/4 inch NPT — with the socket included
The default replacement for a full-height tank, and the one to start with: flexible, so it goes in where a rigid rod will not clear the ceiling, and…
See it on Amazon →Magnesium anode rod, 32 inch
The shorter version, for shorter tanks and lowboy heaters. Measure before you order: a rod that is too long will not seat, and one that is too short…
See it on Amazon →Aluminium-zinc rod, 44 inch — for the rotten egg smell
If the hot water smells of sulphur, the usual cause is bacteria reacting with a standard magnesium or aluminium rod. Switching to an aluminium-zinc…
See it on Amazon →Who actually built yours
Three companies build the tanks. Everything else on the shelf is a name on someone else's steel, and none of this is printed on the box.
Rheem — Rheem, Ruud, Richmond, and the retail lines
One family of brands, with Ruud inside it since 1959, and a Japanese parent since 1988. The store lines and the contractor lines come out of the same company under different names.
A.O. Smith — State, American, Reliance, U.S. Craftmaster, John Wood
Twenty-seven brands on the official list. A 2019 federal recall covered the same defective heater under seven of those names at once, which is the clearest proof the badge is not the machine.
Bradford White — not sold in any big box store
Employee-owned, founded 1881, three American plants. Sold only through plumbing wholesalers to licensed plumbers, on purpose. You cannot buy one online, and that is the company's own policy.
Whirlpool — a licensed name
Whirlpool Corporation's own brand-licensing page lists water heaters as a licensed category. The company that built your washer did not build that tank.
The rod that decides the tank
The anode corrodes instead of your tank. When it is gone, the tank starts to rust — that is the manufacturer's own wording, not ours. Match the length to your tank and the thread to your fitting before ordering: 3/4 inch NPT is the common one, and a flexible rod is what you need when there is no ceiling clearance above the heater.
Flexible magnesium anode rod, 42 inch, 3/4 inch NPT — with the socket included
The default replacement for a full-height tank, and the one to start with: flexible, so it goes in where a rigid rod will not clear the ceiling, and the listing includes the 1-1/16 inch socket the job needs. Magnesium is the usual choice for fresh water.
Magnesium anode rod, 32 inch
The shorter version, for shorter tanks and lowboy heaters. Measure before you order: a rod that is too long will not seat, and one that is too short protects less of the tank.
Aluminium-zinc rod, 44 inch — for the rotten egg smell
If the hot water smells of sulphur, the usual cause is bacteria reacting with a standard magnesium or aluminium rod. Switching to an aluminium-zinc rod is the cheap first move before anyone talks to you about a new heater.
Powered anode rod (impressed current)
Instead of a metal that dissolves, a small continuous current from a plug-in adapter. It does not deplete, so it is not replaced on a schedule, and it is the other answer to the smell. Costs several times a sacrificial rod up front.
1-1/16 and 1-1/2 inch socket set for the job
The hex head on top of the tank is usually 1-1/16 inch, and it has often been there for years. If your rod does not come with a socket, this is the part people discover they are missing halfway through.
Before you replace the whole thing
A rod plus an hour of labour against a new heater installed. The arithmetic is usually not close.
Hiring it out: roughly $200 to $500
A plumber to inspect and replace the rod, parts and about an hour of labour. Worth it if the tank is high, the plumbing is tight, or the old rod is seized.
A new heater installed: roughly $1,200 to $1,800
And a 50-gallon gas unit can reach three thousand two hundred depending on type and region. That is the number the rod is standing between you and.
Read the serial plate: what the first digits mean
| Maker | How the date is encoded |
|---|---|
| Rheem · Ruud · Richmond | Month, then year, then a plant-line code: a serial starting 1209 is month 12 of 2009 |
| A.O. Smith · State · American · Reliance | Year first, week second: a serial starting 2037 is week 37 of 2020 |
| Bradford White | First two characters, on a rotating 20-year letter cycle (the maker publishes the key) |
The episodes behind this page
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