How old is my Rheem furnace or AC?

By Dana Whitlock. Updated October 2026. Widely documented.

Rheem scatters letters through its HVAC serials, and only the last one counts. The two digits right after it are the week of manufacture and the two after those are the year. In 7143W1519143722, the last letter is W, followed by 15 and 19, so week 15 of 2019, which is April.

Many Rheem rating plates make this unnecessary. Check the upper right corner of the plate for 'MFD.' followed by a month and year, such as MFD. 03/94. That printed date comes from the factory and beats any decoding. The letter-then-week-then-year rule is Widely documented. Rheem's own recall notices describe it, and inspector photos show it matching the printed MFD date.

Where to find the label on a Rheem furnace

Rheem gas and electric furnaces and air handlers have the rating plate inside the front door. Set the thermostat to off and turn off the unit's service switch before taking the door off, and read the plate by flashlight without reaching into the cabinet. The CPSC's 1999 notice on Rheem electric furnaces described the identification plate on the front of the unit. Outdoor condensers and heat pumps carry the plate on a side panel. Anything held on with screws stays closed. A licensed HVAC technician can read those labels for you.

How to read the code

Rheem HVAC serials vary in length and can have letters scattered through them, which is why the instruction is to find the last letter rather than count positions. Take BL259M221500247: the last letter is M, the next digits are 22 then 15, so week 22 of 2015, late May. Or W421724596: the only letter is W, then 42 and 17, so week 42 of 2017, mid-October. Weeks run 01 to 53. If the two digits after the last letter are 00 or above 53, you have the wrong letter or the wrong number. Years 40 and above read as 1900s; anything lower is 2000s.

Real serials in this code

When the format changed

Rheem has used this date code on its heating and cooling products since at least the 1980s. A 1999 CPSC recall of Rheem electric furnaces and air handlers spelled it out: the date code is the four digits after the letter M, week first, then year, and units with codes 3592 to 4595 were sold from August 1992 through December 1995. A 2009 Rheem oil furnace recall used the same idea for units sold from 2006 to 2008. Two cautions. Rheem water heaters use completely different serial rules, so do not mix them up. And very old units from before the 1980s sometimes put the week and year at the very end of the serial instead. For those, rely on the printed date or Rheem's warranty lookup.

Who makes Rheem

Rheem Manufacturing makes Rheem and Ruud heating and cooling equipment; Rheem lists Ruud, WeatherKing and others in its family of North American brands. Ruud furnaces and air conditioners use the identical last-letter date code, so this page's method applies to them as well. Rheem systems are sold through independent HVAC contractors and distributors across the US.

How sure is this?

Widely documented. Rheem doesn't publish this code; it comes from recall notices, service literature and inspector references. We tested the rheem ruud hvac rules against 5 serials, 2 of them with a date known from a recall notice, a printed label date or the maker. None decoded to a wrong year; codes whose year mark repeats show every possible reading. Always confirm with Rheem's serial lookup before you spend money on the answer.

Quick notes

• Read the printed MFD date first. It is usually in the upper right corner of the plate.
• Use the last letter in the serial. Some serials carry several, and the earlier ones are plant or product codes.
• Do not apply a Rheem water heater chart to a furnace or air conditioner; the codes differ.
• Write down the full model and serial. Rheem's warranty registration site asks for both.