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Clean filter could actually signal trouble

(ran HC)

Question: Our air-conditioning filter isn't getting dirty. Could that mean we have a problem?

Answer: If you have excessive utility bills, uncomfortable rooms or other problems that seem to be affecting the performance of your heating or cooling system, get the ducts checked for leakage. The duct systems are often the cause of many problems in a home, and, unless you have a professional check it out, you might never know the problem is there.

Researchers at the North Carolina Alternative Energy Center tested a home in which the furnace filter never seemed to get dirty. What they found was a hole in the return duct in the home's heating and cooling system.

As a result, when the heater or air conditioner was operating, the bulk of the air coming into the system was coming from the outdoors. Very little air actually traveled through the filter, so it never got dirty.

They found a similar problem in another home in which the building contractors forgot to remove blocking material used to brace wooden framing material during construction. On one side of the material was the return filter grille and filter and on the other side was the air handler, which was straining to draw air from the home. Removing the blockage opened the air pathway, and the air flowed normally through the system and through the filter.

Ken Sheinkopf is director of development for the Florida Solar Energy Center. Write to him at the Florida Solar Energy Center, 1679 Clearlake Road, Cocoa, FL 32922.