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Heating/AC and figuring ages

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I am "relatively" new to the business, and was wondering if anyone had some input on "dating" furnaces and AC? I notice that alot of the newest models have a manufacured date on them, but the older ones make you read into the model/serial; #'s. Is there any easy way to read into these numbers for each different manufacturer? I have the Carrier Blue book, but it only goes to '93. I figure too that you could call the manufacturer while on the site and ask if they could tell you, but I would like to save time! Water heaters seem to pose the same problem.

Any input would be helpful!!


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This came up on the old TIJ a while back and a bunch of us put our 2 cents into the pot and came up with some decent stuff. I was supposed to follow through and someone's daughter was going to create a little chart or something like that. I completely forgot about it. [:-banghead]

I'll see if I can't find the data and post it here and then maybe I'll remember to get back on compiling that list.



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I have a Preston's Guide (1965 - 2000), and it has just about everything I've run across. The numbers are organized a little wierd sometimes, so you really have to go to the manufacturer and troll the whole section to be sure. It's not cheap though, about $70 when I bought mine a year and a half ago.

Brian G.

Love the Ones With the Date on 'Em

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I have the Carrier Blue Book and The Preston Guides - Both go back to the mid 60's. If yours doesn't have them someone must have stole the pages or??? If the A/C was made before the mid 60's, it would be reported by me as:

"Working beyond its normal life-span. ANY remaining service life is a gift. Replace or keep warranty in place if you can get one".

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Compliments to this site!!! Never thought I would get responses this quick! Never heard of the Preston Guide? I'll check the internet to see if I can find it. If I cant I'd appreciate hearing where to find it. If anyone else has any magical answer to my original question, I'd love to hear from you.

Thanks again guys!


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I found some of that info.

The great majority of gas furnaces that I see are made by Carrier and sold under a variety of brand names - Carrier, Rheem, Bryant and others. These are identified by the first four digits of the serial number by week and year beginning around 1980. Before that, they used the first two digits as the week of the year and a letter to represent the year, beginning with R for 1964 skipping the letter z and ending in 1979 with the letter H.

Trane furnaces have a long serial number with the week and year appearing late in the number immediately after the letter F.

Amana uses the code Blackhorse. S=1969, E=70, B=71, L=72. It goes in 10 year cycles, so:

B=71, 81, 91, 01 H=76, 86, 96, 06

L=72, 82, 92, 02 O=77, 87, 97, 07

A=73, 83, 93, 03 R=78, 88, 98, 08

C=74, 84, 94, 04 S=79, 89, 99, 09

K = 75, 85, 95, 05 E=80, 90, 00, 10

Lennox - Before '74 lst two digits equal the year, next digit the month. ex: 724XXXX = April 1972. After '74 first two digits equals the plant, 3rd and 4th the year, 5th (A letter) equals the month. A=Jan but I is not used.

On old oil furnaces that look like they are from the WWII era I open up the air handler and look at the blower drum. A lot of them have the date stamped right there on the drum housing in purple ink. 1946, 1947, etc..

Thermo-Pride does not code their units by serial number but they do keep a record of every unit sold. You can contact them directly, give them the model and serial number and they can tell you when it was shipped from the factory.


Note: they skip the letters I, O, Q, U, Z.

Year of make indicated by 3rd letter in the serial number.

1971 - A 1992 - A

1972 - B 1993 - B

1973 - C 1994 - C

1974 - D 1995 - D

1975 - E 1996 - E

1976 - F 1997 - F

1977 - G 1998 - G

1978 - H 1999 - H

1979 - J 2000 - J

1980 - K 2001 - K

1981 - L 2002 - L

1982 - M

1983 - N

1984 - P

1985 - R

1986 - S

1987 - T

1988 - V

1989 - W

1990 - X

1991 - Y



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You lost me on the explanation about Carrier. Beginning with R in 1964, skipping letter Z and ending in 1979 with H? Which way are you working in the alphabet ascending or descending...either way I run out of letters before years?

So everything is in the SERIAL #, and not the MODEL #? Carrier Blue Book only gives the Model #. I think Serial # sounds right though.

Any input on the Water Heaters?



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R=64, S=65, T=66, U=67, V=68, W=69, X=70, Y=71, A=72, B=73, C=74, D=75, E=76, F=77, G=78, H=79

Yes, serial number.

Here's some water heater data. There are only a few manufacturer's of water heaters in the U.S.. They manufacture more than 100 various brands.


American - 1st two digits equal the year, next to the week.

AO Smith - 1st letter equals the month and the next two digists the year.

Bradford-White/Lochinvar - 1st letter in the serial number is the year of manufacturer with A being 1964 or 1984 (They use a 20 year cycle) They skip the letters I, O, Q, R, U, V to make the full cycle. The second letter is the month A=January through M = December (I is left out)

Rheem - 1st two digits equal the month, next to the year.

State/Reliance/Sears - Letter that equals the month followed by the year.

OT - OF!!!


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A lot of the time you might see a serial number such as 3479xxxxx or 2494xxxx.

The first one would read the 34th week of 1979, the second one would read the 24th week of 1994. BE CAREFUL with this method, use a good eye to approximate the date before using this method.

You can use this in conjunction with the other methods mentioned here.

By the way, what is your real name?

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Originally posted by hausdok

. . . The great majority of gas furnaces that I see are made by Carrier and sold under a variety of brand names - Carrier, Rheem, Bryant and others. . . .

Rheem & Ruud are not made by Carrier.

Also, the week & year after F sounds like Rheem/Ruud, not Trane.

- Jim Katen, Oregon

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