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Miller Water Heater Age by Serial Number — Free Lookup

Rheem

Enter the serial number from the rating plate (the silver data sticker on the upper side of the tank; on tankless units it is inside the cover on the right side). Works for Rheem, Ruud and Richmond — many Rheem plates also print the manufacture date directly as "MFG. DATE".

How Old Is Your Miller Water Heater?

Miller water heaters are built by Rheem Manufacturing, so they use Rheem's date code: month, then year, in the first four digits after any letter prefix. Enter your serial in the free decoder above for an instant answer, or follow the guide below to read it yourself.

Where to Find the Serial Number

Check the rating plate on the side of the tank — a silver or white sticker, usually in the upper half, that lists the model number and serial number together. The date lives in the serial, not the model number. On older tanks the sticker can fade; a phone photo with the contrast bumped usually makes the digits readable.

How the Miller Serial Format Works

Rheem encodes the date as MMYY — month first, then year — in the first four digits after any letter prefix:

Worked example — RN1009A22108:

  • RN = plant code (ignore)
  • 10 = October (month)
  • 09 = 2009 (year)
  • A and the remaining digits = production sequence
  • Result: manufactured in October 2009

Letter prefixes are plant codes. Serials often start with R, RH, RN, RHNG, or a single letter — none of these are part of the date. Skip them and read the first four digits you find. Some old units used week-based formats; if the digits don't decode as a valid month, the decoder says so rather than guessing.

Why Your Miller Water Heater's Age Matters

  • Lifespan. Tank water heaters average 8–12 years of service. Past that, internal corrosion makes tank failure — and a flooded floor — far more likely.
  • Warranty. Miller tanks carried standard warranty terms counted from the manufacture date, not the install date. The serial tells you whether a repair might still be covered.
  • Replacement planning. A unit past 10 years is on borrowed time. Knowing the date lets you shop for a replacement calmly instead of during an emergency.

Sources

Brand ownership and serial format verified against the InterNACHI water heater dating chart and InspectApedia's Rheem age decoder.

Frequently asked questions

Who makes Miller water heaters?
Miller-branded water heaters are built by Rheem Manufacturing. The InterNACHI water heater dating chart groups Miller with the Rheem production lines, so Miller serials carry the same month-year date code as Ruud, Richmond, and GE units. (Miller is better known for furnaces — the water heaters are a separate line.)
How do I tell the age of a Miller water heater from the serial number?
After any leading letter prefix, the first two digits are the month and the next two are the year. For example, serial RN1009A22108 means October 2009 — month 10, year 09. Letters before the digits are plant codes; the date always follows them.
Where is the serial number on a Miller water heater?
On the rating plate — a silver or white sticker on the side of the tank, usually in the upper half, that lists the model and serial numbers together. If it has faded, photograph it and boost the contrast; the first four digits after any prefix are all you need.
How long does a Miller water heater last?
Tank-style units average 8–12 years. Flushing sediment regularly and replacing the anode rod on schedule can push a unit toward the longer end, while hard water shortens it.
My Miller serial starts with letters. How do I read it?
Leading letters are plant codes such as R, RH, RN, or RHNG — not part of the date. Skip them and read the first four digits you find as month and year: RN1009A22108 decodes to October 2009.