How old is my General Electric (legacy central HVAC, pre-1982) furnace?

Serial number age decoder for General Electric (legacy central HVAC, pre-1982) furnaces: 3 format eras, the decode rule in plain English, transcribed tables, and the official lookup.

• General Electric (legacy central HVAC, pre-1982) furnace serial numbers in the 1960 to 1989 format encode the year as digit 7 = last digit of year; decade presumed (8 = 1968/1978/1988) and the week as digits 8-9 -> week 09 (source: building-center.org).
• Example: serial 359952809 decodes to week 9 of 1968 or 1978 or 1988.
• The 1960 to 1989 format is ambiguous: Single year digit; 9-digit numeric collides with other brands.
• General Electric (legacy central HVAC, pre-1982) furnace serial numbers in the 1965 to 1985 format encode the year as letter 2 (table below) and the month as letter 1 (A=Jan..M=Dec, I skipped) (source: building-center.org).
• Example: serial HM409295 decodes to August 1976.

Format eras

• 1965 to 1985 VERIFIED
  AA######letter 2: A=1965 B=1966 C=1967 D=1968 E=1969 F=1970 G=1971 H=1972 J=1973 K=1974 L=1975 M=1
• 1965 to 1985 VERIFIED
  ######AAlast letter, same table as the leading-letter style
• 1960 to 1989 VERIFIED
  #########digit 7 = last digit of year; decade presumed (8 = 1968/1978/1988)

How to read the serial

1965 to 1985 formatVERIFIED

Shape AA###### · example HM409295 · confidence high

Year

letter 2: A=1965 B=1966 C=1967 D=1968 E=1969 F=1970 G=1971 H=1972 J=1973 K=1974 L=1975 M=1976 N=1977 P=1978 R=1979 S=1980 T=1981 V=1982 W=1983 X=1984 Y=1985 (I, O, Q, U skipped)

Week or month

month = letter 1 (A=Jan..M=Dec, I skipped)

Example: serial HM409295 decodes to August 1976.

1965 to 1985 formatVERIFIED

Shape ######AA · example 409295HM · confidence high

Year

last letter, same table as the leading-letter style

Week or month

month = second-to-last letter

1960 to 1989 formatVERIFIED

Shape ######### · example 359952809 · confidence medium

Year

digit 7 = last digit of year; decade presumed (8 = 1968/1978/1988)

Week or month

week = digits 8-9 -> week 09

Example: serial 359952809 decodes to week 9 of 1968 or 1978 or 1988.

Where the data plate is on a furnace

Inside the furnace: remove the upper (burner) access door and look on the inside of the door, on the blower compartment wall, or on a sticker facing you at the burner deck.

General guidance, not brand-specific: the owner's manual or the installer can point to the exact spot. See the data plate guide.

For scale only: the InterNACHI Standard Estimated Life Expectancy Chart for Homes lists Furnace at 15 to 25 years of expected service (nachi.org). That chart is a guideline, not a prediction for your unit.

What we could not confirm

• The 1965 to 1985 format is documented but not decodable here: letter-year rule without a transcribed table.
• No official online lookup URL was verified for General Electric (legacy central HVAC, pre-1982).
• Pre-1982 GE central AC/furnaces: 9-digit numeric with Y WW in the last 3 digits, or two-letter month/year codes at the start or end (HM409295 / 409295HM = Aug 1976). Any unit still bearing GE is far past service life.

Sources

• https://www.building-center.org/general-electric-hvac-age/
• img: GE-hvac-1.jpg
• img: ge-hvac2.jpg (transcribed)
• img: ge-hvac3.jpg

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