There are two serial number formats:

1) 2002  to present - If the serial number is a 9-digit combination of letters and numbers that starts with a number, then the first number is the year. Beginning in 2010, the first two digits are the year. Examples of each type are shown below. Many units have the date of manufacture stated below the serial number. 

2) 1983 to 2001 - If the serial number starts with a letter, then that is the encoded year. W = 83, X = 84, Y = 85, S = 86, B = 87, C = 88, D = 89, E = 90, F = 91, G = 92, H = 93, J = 94, K = 95, L = 96, M = 97, N = 98, P = 99, R = 00, Z = 01. So the serial number shown below indicates that the furnace was manufactured  in 1992. Notice that the year that the letter indicates is corroborated by the 1990 year of the ANSI rating above it, which should be the same year or just a few years earlier.

    Many, but not all, furnace data plates will also state the month and year of manufacture somewhere on the data plate, like the examples below.

    To determine the age of a American Standard air conditioner or heat pump, go to our blog post How can I determine the age of an American Standard air conditioner or heat pump from the serial number?

    To determine other key specs of your HVAC system, see one of these other blog posts: 

• How can I find out the SEER of my air conditioner?

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• How can I find out the size of my air conditioner? 

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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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  To learn more about heating and air conditioning systems, see these other blog posts: 

• Is the energy efficiency of the furnace part of the SEER rating of a central air conditioning system?

• My air conditioner won't turn on. What's wrong? 

• What color should the flame be in a natural gas furnace?

 • Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• What is the minimum slope of a flue connector for a gas furnace or water heater? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• Is a furnace allowed in a bedroom, bathroom, or an adjoining closet?

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Can the return air be in the same room as the gas furnace?

• Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.