Acceptable CCF usage for gas water heater?

At a 1/2 P.S.I. you have more air in your lungs than the heater has gas. Make a box out of cardboard 1'x1'x1' (a cubic foot) then cut it in a little more than half. The smaller volume half is what your heater has consummed (all day??? or per hour when firing???) You may only take one shower per day and you may be the only person in your dwelling, but you have a lot of temperture drop from the tank to the fixtures 130F down to 120F. Newer heaters in a well insulated home usually run 2-3 degrees variance. This cooling of the heater causes it to run more often to maintain your 130F setting. Try wrapping the heater in a thermal blanket if you're
concerned about gas usage and/or are looking for higher efficiency.

It's worth keeping. The new tanks are 300-500 dollars just for the unit and while you may be able to do it yourself the unit you have right now appears to be working very nicely. Just get a heater thermal blanket (maybe 50 bucks) and some pipe insulation for your sizes of pipe for the HOT side from the tank to as near your fixtures as you can get. The best rule of thumb with water heaters is if they don't leak and don't cause you the national debt in energy costs is DON'T TOUCH IT. Water heaters can leak right out of the box or they can last 30, 40, 50 years with no problem. My first one lasted 29 years and the only reason I took it out was my family was growing and I needed more draw down at the same pressure and temperature. The one I have now is 10 years old going on 100.

Nope not for you and I. Just the manufacturer