But, all water heaters have a Rating Plate that lists important data such as the model and serial numbers, manufacturing companys name, length of warranty, wattage of elements installed (on electric models), gallon capacity, input BTU rating (gas models), and more.

It includes the manufacture date, as well as information on the size and capacity.

Some manufacturers, including Rheem, made it easy by incorporating the month and year built into the first 4 digits of the serial number.

For instance, the picture below shows that this Rheem water heater was manufactured in December of 1991 (1291).

Other manufacturers use different formats, but in a similar fashion.

The other info you see relates more to service technicians, and shouldnt be needed by the average homeowner.

This 50 gallon electric tank was built in August of 1984, and came equipped with 4000 watt elements.

Its a little harder to find the info on the AO Smith plate, but its all there.

The year of manufacture is noted by the first letter of the serial number, the month is the second letter.

This is a 40 gallon electric water heater, model number MI40L6DS13, manufactured in June of 2002.

It is designed to operate with a maximum of 150 PSI water pressure, but was tested to 300 PSI at the factory for your safety.

Lochinvar Serial Number Decoder