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Homefix: Idle hot water stinks up the house

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Q: I'm hoping that you can help with a smelly hot-water issue we have had for years. Whenever we return from a few days away, the hot water in our house smells like sulfur/rotten eggs. We usually have someone come in and run the hot water every couple of days while we are away, but the most recent person didn't know to run the hot water, and when we returned after two weeks, our house stunk.

We replaced our hot-water tank 12 years ago, and this stinky problem has been going on for more than eight years. We didn't connect the problem with our water tank, since it was relatively new when we first noticed the problem. Have you heard of anything like this? Do you think replacing our hot-water heater/tank would do the trick?

A: Replacing the tank might help, but the odor is most likely caused by a chemical reaction between your water supply and the sacrificial anode rod inside the water heater's tank. The anode is designed to degrade inside the tank to protect the lining of the water heater from rust and corrosion. Most water heaters have either an aluminum or magnesium anode. As the water heats up, a chemical reaction occurs that forms hydrogen-sulfide gas, which creates the rotten-egg smell at the faucets. This generally happens when the hot water is not used for extended periods of time.

Changing the anode metal from aluminum to magnesium (or vice versa) might help, but both will react about the same to the water supply.

There are three alternatives that might do the trick:

1. Use an aluminum/zinc-alloy anode rod. The zinc appears to alter the chemical reaction that produces the odors. There have been some instances -- homes with water softeners -- where the aluminum/zinc anode did not help. If you have a water softener and an odor problem, you might want to choose an electrical anode rod.

2. Install an electrical anode rod, which adds a small electrical charge to the hot water preventing the chemical reaction from taking place.

3. Add hydrogen peroxide to the hot-water tank. This requires shutting off the water supply, partially draining the tank and removing one of the water pipes on the tank to add the peroxide. The peroxide is not a permanent repair and would have to be repeated periodically.

(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 286, Evansville, IN 47702, or e-mail him at d.Barnett@insightbb.com. Please include a SASE with your questions.)

(Distributed by Scripps Howard News Service, www.scrippsnews.com)