The first two numbers in the serial number, which may appear after one or two letters, are the year of manufacture of an A.O. Smith water heater. So the data plates shown below indicate that the water heaters were manufactured in 1989 and 2004.

    And here’s an oldie from 1978. A slightly different format, but the year of manufacture is still the first two numbers after one or two letters:

    For an A.O. Smith tankless water heater, go to How can I tell the age of an A.O. Smith tankless on-demand water heater from the serial number?To determine the age of another manufacturer/brand of water heater, go to How do I determine the age of my water heater? Also, see our blog posts How can I determine the age of a water heater if the serial number is missing or decoding it is impossible? and What are the most common installation mistakes with water heater replacement? and Are water heaters required to be raised off the floor? and What's that powdery crust on the pipe connections at the water heater? 

   To find the age of other home components, go to How can I find out the age of a roof? and How do I determine the age of an electrical panel? and How do I determine the age of my air conditioner? For life expectancies, visit What is the average life expectancy of the components of a house?

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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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Here’s links to a collection of more blog posts about WATER HEATERS: 

• Is a water softener bad for my water heater?

• Where are gas water heaters not allowed to be installed? 

• Is the minimum size water heater inlet pipe 1/2" or 3/4" according to the building code?

• Can you use a light switch for a water heater disconnect? 

• How can I tell if a water heater is HUD-approved for mobile/manufactured homes?

• Why is the water heater older than the house? 

• Does a water heater need a shut-off valve? 

• Why should a tankless water heater have an isolator/service valve kit installed?

• When was a gas water heater first required to be elevated 18 inches above a garage floor?  

• Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home? 

• What is the purpose of a thermostatic mixing valve above a water heater? 

• Does a tankless gas water heater still work with no electricity during a power outage?  

•  Why do water heaters have a sacrificial anode? 

• What is the difference between a manufactured/mobile home water heater and a regular water heater? 

• Where do I find the water heater in a mobile home?

• Does a tankless water heater in an attic require a drain pan? 

• Does an electric water heater require a disconnect? 

• Is a catch pan and drain piping required for a replacement water heater?

• What is the difference between a single element and dual element electric water heater? 

• What is an FVIR water heater?

• What is a heat pump water heater?

• What is a dielectric union?

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