The first two numbers of the serial number are the year of manufacture, and the second two numbers are the week, so the serial number shown below means the water heater was manufactured on the 9th week of  2017. 

    Some serial numbers will have a single letter after the first four numerals and others, like the one above, are all numbers. Takagi water heaters produced before 2010 did not have the year of manufacture encoded in the serial number, and the one shown below is an example. So we suggest calling their customer service line at (949) 770-7171 for help if you suspect the unit is older, or the first two numbers don’t seem right compared to the condition of the unit. They will provide year of manufacture for any serial number. Checking the ANSI approval year on the data plate will give you a good idea of an approximate age. This had a 2004 ANSI.

    To determine the age of another manufacturer/brand of water heater, go to How do I determine the age of my water heater? Also, see our blog posts How can I determine the age of a water heater if the serial number is missing or decoding it is impossible? and What are the most common installation mistakes with water heater replacement? and Are water heaters required to be raised off the floor? and What's that powdery crust on the pipe connections at the 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? 

• Where are gas water heaters not allowed to be installed?  

• 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?

• 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?

• What is a heat pump water heater?

• What is a dielectric union?

• 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'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.