The third and fourth numbers in the serial number, usually after several letters, is the year of manufacture of a Rheem water heater. So the manufacturer’s data plate below indicates that it was made in 2001.

    Newer Rheem water heaters, like the one with the label below, make it easy for you: the manufacture date is stated to the right of the serial number.

   By the way, look for the data plate of older Rheem water heaters on the top of the water heater instead of the side. The same serial number system is used as today, but there may be a gap between the first and second numbers. The example below was manufactured in August, 1969.

Also, the Rheem tankless water heaters use the same system of second two numbers in the serial number are the year of manufacture. The one below is 2014.

    Rheem has manufactured water heaters under multiple other brand names over the years. Many have been discontinued for years, but a few older water heaters with these nameplates may still be around. If you look carefully at the bottom of the data plate, you will see the name of the actual manufacturer in fine print. This is important to look for, because some retailers have switched manufacturers over the years. Here’s some of them, and they all use the same Rheem serial number code shown above:
• ABS water heaters
• Aqua Therm water heaters
• Citation water heaters
• Energy Master water heaters
• Vanguard water heaters
• Vista Therm water heaters
• Cimarron water heaters
• Coast To Coast water heaters
• Intertherm water heaters
• Lowes water heaters
• Mainstream water heaters
• Miller water heaters
• Montgomery Ward water heaters
• Professional water heaters
• Servi-Star water heaters
• True Value water heaters 

        To determine the age of another manufacturer/brand of water heater, go to How do I determine the age of my 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:

• Are water heaters required to be raised off the floor? 

• 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?

• Can you wire a 240-volt water heater with 120 volts? 

• Is it alright to have a shut-off valve on both the hot and cold water pipes at a water heater?  

• What is the minimum clearance to doors and windows for an outdoor tankless gas water heater? 

• What is required clearance for access and working space in front of an electric water heater? 

• 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? 

• Does a tankless water heater require a pressure relief valve?

• When is a water heater drain pan required?

• Why is there water in my water heater drain pan?

• What does it mean when a water heater Temperature/Pressure Relief (TPR) discharge pipe is "trapped"? 

• Can I leave a gas water heater in place when remodeling a garage into a family room or bedroom? 

• 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?

• What's that powdery crust on the pipe connections at the water heater? 

• What are the most common installation mistakes with water heater replacement?

• Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises? 

• What can I do to make my water heater last longer?

• How can I determine the age of a water heater if the serial number is missing or decoding it is impossible? 

• How does a hydronic heating system work?

• What is the difference between a regular water heater and a direct vent water heater? 

• What is the difference between a regular water heater and a power vent water heater?

• What is backdrafting at a gas water heater? 

• How do I determine if a water heater is gas or electric?

• What does it mean when a gas appliance (water heater, furnace, or range) has been "red tagged"?  

• What's the valve with the flip-up handle on the water heater for?

• Why is an older water heater an insurance problem?

   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.