Check warranty, energy factor of water heaters

By James Dulley, Special to the Times
Published November 24, 2007

Q: I need to replace my old electric water heater with one that will last longer and use less electricity. Other than the warranty, is there really much difference among the various models?

A: Electric water heaters are relatively simple devices, so other than the all-plastic models, there are not many differences among the various manufacturers. The length of the warranty is actually an excellent method to compare the relative quality among them. Ten- to 12-year warranties are good and some models offer lifetime warranties.

When comparing water heaters (electric or gas), the efficiency is rated by its EF (energy factor). For new electric water heaters, EFs range from about 0.85 to 0.95. For a typical family of four, upgrading from an old 0.80 model to a 0.95 one can save about $100 of electricity annually. All water heaters' specifications list the EF and it also is shown on the new product label.

All electric water heaters have two electric heating elements. These electric elements are nearly 100 percent efficient at converting electricity into heat for the water. The differences in efficiency and annual electricity usage among the various models are determined by how much heat is lost through the tank walls.

The heat loss through the tank walls is effected by the amount and type of insulation. The most efficient standard electric water heater tanks have 3 inches of foam insulation between the glass-lined steel tank and the outer steel shell.

There is an all-plastic electric water heater that is guaranteed to never leak because there is no steel tank to corrode. The inner tank, which actually holds the hot water, is made of fiberglass-reinforced plastic. It is shaped similarly to a large test tube with rounded ends for maximum efficiency.

The outer shell is made of high-density polyethylene (similar to a plastic garbage can), which is extremely durable and virtually indestructible. The relative shapes of the inner tank and outer shell provide room for extra foam insulation at the top, where the water is hottest. This makes it one of the most efficient electric water heaters available.

A key to lower water heating costs is to select the smallest tank size you need. A smaller tank has less surface area so it loses less heat. This may require some minor changes in your family's hot water usage patterns, but it will save electricity. Optional extra powerful heating elements are available to provide more hot water from a smaller tank.

Another efficiency option is a built-in timer. This can switch off the heating elements for periods when hot water is not needed, such as during weekdays when you are at work and the children are in school. 

James Dulley is a mechanical engineer and do-it-yourselfer. Send questions to James Dulley, The Sensible Home, St. Petersburg Times, 6906 Royalgreen Drive, Cincinnati, OH 45244. Visit his Web site at www.dulley.com to tour his energy-efficient home, post questions for other readers and find other information.

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Electric water heaters

The following companies offer electric water heaters. All phone numbers are toll-free.

A.O. Smith: 1-800-527-1953, www.hotwater.com.

American Water Heaters: 1-800-999-9515, www.americanwaterheater.com.

Maytag: 1-800-360-8807, www.maytagwaterheaters.com.

Rheem: 1-800-621-5622, www.rheem.com.

State: 1-800-365-8170, www.stateind.com.