Unfortunately most manufacturers of water heaters do not clearly state the manufacture year on the data plate or label but luckily the year of manufacture is typically coded in the serial number. Numbers 3 and 4 are the year.This article is a quick reference guide for the most common manufacturers of water heaters.The first * represents the factory code, the letter that follows represents the month (see below). In July of 2004 AO Smith stopped using the factory designation and the serial number appeared like this: F04*******.In this example, the water heater was built on the 36th week of 2018.In this example, the water heater was built on the 18th week of 2013.The second and third digits are the year.In this example, the water heater was built on the 10th week of 2012.AO Smith has been a leader of water heater technology, including the development of the glass lined tank, which is now an industry standard.Īlthough water heaters are sold under their own name, AO Smith also manufactures models under the following brands: GSW John Wood Whirlpool US Craftmaster American State Reliance Kenmore Takagi and Lochinvar.ĪO Smith uses four primary styles of serial numbers: The AO Smith company has been around since 1874, but it didn't begin producing residential water heaters until 1939. If you own a Ruud water heater you can follow the Rheem serial styles above. Rheem also produces and sells water heaters under the Ruud name.

In this example, the water heater was built the 18th week of 2014.

In this example, the water heater was built in May of 2005.

In this example, the water heater was built in August of 2004.

In this example, the water heater was built in November of 2014.

In this example, the water heater was built the 14th week of 2015.

In this example, the water heater was built in August of 1984.

The serial number will begin with: R RN RNG RHNG etc.

However, if you prefer to figure it out on your own, they use 5 different formats: Simply enter your water heater's serial number and the age of your water heater will be displayed. Rheem is a major player in the water heater industry, they also offer an easy method on their website to find the build date.

State water heater age