Water heater serial numbers encode the manufacturing date differently by brand. AO Smith uses the first four digits (YYWW), Bradford White uses a 20-year repeating letter code, and Rheem uses a month-year (MMYY) format. Always decode the serial before replacing.
Why Water Heater Age Matters
Water heaters typically last 8-12 years. Knowing the exact age helps determine whether to repair or replace, especially when evaluating tank corrosion or anode rod status. A unit over 10 years old is a strong replacement candidate.
AO Smith Serial Decoding
AO Smith and its sub-brands (State, Reliance) generally use a 10-digit serial where the first four digits are the year and week. For example, 1914... means the 14th week of 2019.
Bradford White Letter Codes
Bradford White uses a unique letter format for year and month. The first letter is the year (e.g., A=2004 or 1984), and the second is the month. This 20-year cycle requires you to also inspect the visual style of the unit.
Rheem Format
Rheem often uses a format where the first four digits indicate the month and year of manufacture (MMYY) or a letter followed by MMYY. Always verify the manufacturer stamp.