Often if agents look at the serial plate of main systems, and don't see the age clearly labeled on them, they will leave it to home inspectors to determine. That's not necessary, as you'll see below with a quick reference guide to some of the most common water heaters and a link to more water heater information. For brevity & what's most important, I'm only focusing on the year of manufacture. See the hyperlinks for additional details on the week/month/other information.
Disclosure on Limited Accuracy
Sources are hyperlinked on each row. For a more comprehensive list, go to Building-Center.org's list here. I found their lists to be more accurate/user-friendly than others, though you'll have to do more digging than the guide below since they don't publish a quick reference chart like this one.
Year by Serial # Below (most often 1st 2 numerical digits, w/ some 3rd-4th numerical digits & some lettering systems
American water heater company (1st 2 digits)
AO Smith (1st 2 numerical digits)
Bradford White (see chart)
Craftsmaster (1st 2 digits)
Envirotemp (1st 2 digits)
GE (3rd-4th numerical digits)
Kenmore (1st 2 numerical digits)
Maytag (1st 2 numerical digits)
Raywall (1st 2 digits)
Rheem (3rd-4th numerical digits in tanked styles; 1st 2 numerical w/ tankless)
Rinnai (see chart)
Ruud (3rd-4th numerical digits in tanked styles; 1st 2 numerical w/ tankless)
State (1st 2 numerical digits)
Whirlpool (1st 2 digits)
More
What Size Water Heater do I Need?
Water Heater Lifespan per HUD
Water Heater Cost (Typically $900-$5400 Installed, but $1.4k average)
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