Look at the sticker on the side. This will help you determine the size of the water heater you are interested in. You will see a serial number unique to that unit and some other valuable information, including its capacity in gallons. Furthermore, you need to decide whether you need a short or tall water heater.
Wherever you live in Southeastern PA, All Drains Plumbing will help you install and ultimately maintain your water heater. Joe Canty serves Bensalem, Bucks, and Montgomery County as well as parts of Philadelphia. Visit alldrainsbensalem.com and call for service you can depend on.