I recently moved to a new home and I'm having a problem with a popping noise in the heat ducts. It occurs during the heat cycle, but we notice it more during the cooling-down period. Our builder and heating contractor say they can't do much about it, but I'm sure there must be a fix. Our previous homes didn't have this problem. I also noticed that 26-gauge metal was used for the duct system. Does this thickness meet house building code, or is there no minimum requirement? - N.F.A., Walled Lake, Mich.Answer - When the furnace comes on, forcing warm air through the ducts, the sheet metal used for the duct work expands and some popping occurs.

After the furnace is off, the fan continues to run for a while, cooling the sheet metal and causing it to contract. Again, some popping sounds might be noticeable.

Here are some causes and possible solutions.

- The sheet metal was installed too close to the floor joists. Generally, a 1-inch gap is left between the floor joists and the duct work. The ducts are hung from the joists with metal straps. Sometimes just walking in the area where the ducts are not properly hung can cause a popping, "tin can" noise.

- Panning or cold-air return sheet metal is often nailed to the bottom of the floor joists, utilizing the floor joist's cavity as part of the return air duct. The metal can buckle when you walk across the floor or when heated and cooled.

- The sheet metal was not "creased" during fabrication. The crease allows for expansion and contraction of the sheet metal.

- The ducts are fastened directly to the furnace. Normally, a canvas connector is used to make the connections. This is used to eliminate furnace noises, but can allow for some of the sheet metal's expansion problems.

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- Sheet metal of 26 gauge is allowed under the Uniform Mechanical Code for sheet metal up to 18 inches wide.

One of the easiest solutions to your problem would be to insulate the sheet metal and ducts. The insulation keeps the sheet metal at a more constant temperature and muffles the popping noises, should they occur.

Question - I read an article on how to fix squeaking floors. Our house is 5 years old and some floors are squeaking badly. I am interested in the third device, a drilling jig, or do I understand a better way is to use a screw to go through the carpet with a No. 8, 1/4-inch twist-fast screw? Where could we buy this kind of screw? - C.G., Owensville, Ind.

Answer - No. 8 1-1/4 inch, not quarter-inch, twist fast wood screws can be purchased at most hardware and lumber dealers. I prefer to fix the squeaks by screwing right through the carpet, but remember to be careful not to damage the piles of the carpet. Use a long Phillips-head screwdriver in your screw gun to keep the chuck away from the carpeting.

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