I have an AO Smith 40 gallon natural gas water heater that is almost 8 years old. Our city water is slightly hard. I have only flushed the tank twice in 8 years mainly because I am afraid of breaking the cheap plastic valve off (it leaked after the first flush). I have never replaced the anode.
I have noticed that after the first shower in the AM (during recovery) when I get in to take a shower, it sounds like there are air bubbles for a few seconds. I keep the temperature pretty hot and I suspect that the water heater might be creating a few bubbles during recovery.
I am considering buying a new water heater based on its age, lack of maintenance, and slight fluctuation in water temps. Is this appropriate or premature?

Any recommendations for water heaters out there? I was probably just going to go to Lowe's, home depot, or sears. It seems like heaters are almost a dime a dozen. I don't want anything that requires electricity to operate so when the power goes out we still have hot water. What kind of efficiency is affordable these days?

Thanks-

Gas heaters give you more bank for the buck so stay with gas. You have heard you get what you pay for, right? Actually that was a quote from a water heater salesman. Do not go with the lowest price on a water heater and if they rate them good, better, best try to go better or best. Rheem, Smith, Rudd and many others are all good brands but I can't tell you one brand that is the very best.

I like the AO Smith line. I don't like the drain valves. It seems as the manufacturer doesn't want you to get hurt and the drain valve suffers. I replace the drains with this:

T-537 on

Ball Valves - Legend Products (http://www.superiorspecialty.com/Main/Plumbing/Legend/BallValves.htm)

And add a CAP on the end.

It has very good flow and the cap, prevents leaks caused by accidentally turning the handle.

It's always nice to plan for a replacement. That way you can do it when it's convient.

ConsumerReports.org - Water-heater tips: Gas hot water heater, electric hot water heater (http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/water-heaters/waterheater-tips-205-gas-hot-water-heater-electric-hot-water-heater/overview/)

Seems simple answer is longer the warranty the better insulated and thicker materials used in construction.

Thanks for the advice guys-

A tale about water heaters from my neighbor, a long time plumber.

Several years ago (10 or more) he and a couple others in the firm were invited down to NC by one of the manufactures of water heaters to visit the plant. After touring the assembly line they were fed hot dogs and cokes and a little talk was given by their host.

He relates two interesting facts. First the assembly line was completely automated. The heater was untouched by human hands except for sliding on the outer jacket at the end of the line.
Second, during the talk someone asked, “Which model were you making, (the 5 yr, 7 yr or 10 year). The answer was “Yes”. They are all the same heater; the only difference is the label that is put on them and the warranty you get. They know that x number out of each 1000 will develop a leak at a weld in a 10 year period, but they don't know why. Leaks are always at welds.

So when you pay twice as much for the 10-year model as the 5-year model you are only buying the warranty. The odds of having a tank leak are the same.

Note that the warranty only covers a leaking tank.

A water heater should last at least 12 years. If you are afraid of a leak then you may want to replace it. I personally would get a water alarm from home depot for 10 bucks and wait. When you do replace, stick with rheem manufactoring. They make rheem, ruud, general electric, and others. Home depot is currently showing the g e. Lowe's has whirlpool. I avoid them.
As for the warranty, different models have different additions that make the warranty better, some are insulation factors, some are cost factors on daily use.

Whichever brand you buy have them describe the explosion proof combustion air situation. How it is made, how it works, what you have to do to keep it lit, and it there is a warranty on this part of the heater. Here is why, as the filters start to stop up with lint and dust the water heater starts to burn less efficiently causing moisture to accumulate in the burner chamber and on some of the heaters this causes the filter to rust over and that makes less fresh air which compounds the problem.
It is my feeling that Rheem is the best buy to remedy this situation.