QOur house is nine years old and we have never had the heating and air-conditioning ducts cleaned. Should we have the ducts cleaned? Is it expensive? -- C. Terenick

AMold, dust and other contaminants often build up in ducts. Some of these contaminants are swept into the living area in the air stream and can cause special problems for those with allergies and respiratory disorders. Excessive dust and odors are other possible effects of dirty ducts.

Many contractors offer free evaluations and estimates (check under Duct Cleaning in the phone book). Or if you want to inspect the ducts yourself, remove some of the registers and use a mirror and flashlight to check the interiors of the ducts. If you see a significant amount of debris, often including clumps of mold, it's probably time to call the duct-cleaning contractor, who will use various tools to loosen the debris, then pull it out with powerful vacuum cleaners. The Environmental Protection Agency estimates that duct cleaning typically costs $450 to $1,000, but the actual cost depends on the size and condition of the duct system.

The interval between cleanings can also vary widely, depending on many factors. More frequent cleanings might be needed if there are pets, smokers or people with allergies in a home. According to the National Air Duct Cleaners Association, a Washington-based trade group, intervals of four to eight years are not unusual. The use of high-efficiency filters on furnaces and air conditioners can help keep ducts cleaner.

The NADCA Web site (www.nadca.com) is an excellent source of in-depth information on duct cleaning. The site includes a list of frequently asked questions that includes information on approved methods of cleaning, how to select a contractor and possible health benefits.

I'm installing ceramic tiles in my bathroom and need to remove a radiator to tile under it. How do I do this, or should I work around the radiator? -- J. Davis

You need to shut off and drain the water from the heating system, then loosen the pipe connections on both sides of the radiator. Have some old towels handy to mop up water that might be left in the pipes or radiator.

The new tiles will raise the radiator slightly when you reinstall it, so you might have trouble making the connections again unless there is some flexibility in the pipes.

Removing a radiator sometimes isn't practical, especially in cold weather. It is usually possible to install tiles around the legs and pipes. A tool called a tile nipper, which resembles pliers with sharp cutting edges, can be used to "nibble" tiles into various shapes to fit around obstructions. Some tiles might need to be cut into sections with a snap cutter, then nibbled into shape and reassembled around a leg or pipe. Seal any small gaps with caulk to keep dirt out.

What is a good way to clean and protect kitchen and bathroom counters made of plastic laminate? -- C. Cunningham

Gel-Gloss (www.gel-gloss.com), sold at some home centers and supermarkets, is an excellent cleaner-polish for plastic laminates such as Formica. It contains carnauba wax, which leaves a protective film on the surfaces. This product can also be used on fiberglass and acrylic surfaces, stainless steel, ceramic tiles and chrome fixtures.

If your heating system or air conditioner performs erratically or leaves some areas of the house cold and others warm, here is an excellent tip based on information supplied by reader Frank R. Ackerman of Teaneck, N.J.:

Remove the thermostat from the wall. This usually means removing the cover and the mounting screws that hold a backing plate to the wall. Check the point where the thermostat wires come out of the wall. If there is a gap or hole around the wires, plug it with some spackling compound or a few dabs of caulk. The reason: Puffs of air coming through the hole from inside the wall can adversely affect the thermostat's performance. Ackerman said he solved a major heating problem in his home with this simple repair.

Readers' questions and comments are welcome and should be sent to Gene Austin, Box 861, Blue Bell, Pa. 19422. Send e-mail to austfixit2aol.com.

Questions cannot be answered personally.