Safe cover-ups for unsightly radiators; fireplace economy

Q. Is it safe to make thin cotton cloth covers for unsightly radiators? Will cloth measurably decrease the heat given off? Carol DesLauriers Cieri, Milwaukee

The combustion temperature of cellulose is 450 degrees F., and cotton is about 95 percent cellulose. Assuming the unattractive radiators are steam- or hot-water-operated, light cotton cloth should be safe, but I'd avoid its direct contact with the hot metal. Were it my house, I would use a perforated cloth with holes large enough to transmit a maximum amount of heat but small enough to cover the unsightliness of the radiators.

Have you thought of painting the radiators? Check with a local paint store for a type of paint that would not affect, or be affected by, the resident heat. I'd prefer the paint to cotton.

Q. We want to buy some replacement windows and need to know the relative merits of vinyl and aluminum. Can you help us? Virginia Thorp, Rockville Centre, N.Y.

Steel-frame windows were the big seller some 25 or more years ago, but gradually aluminum windows took their place because the aluminum units were lighter in weight and required no paint. Except for specialty uses, steel windows have all but disappeared from the marketplace. Aluminum windows still hold sway in the residential field, though wood windows have kept their own identity and usage where preferred for their style.

Assaulting the domestic market, especially for residential window replacements, are the polyvinylchloride (PVC) windows that were developed in Western Europe, where they continue to be quite popular. A recent window-replacement study found that the market for vinyl-clad windows is growing and shows strength for the future. The reason? Vinyl windows are inexpensive, they are thermalized to reduce heat loss and gain, they won't pit or corrode, and they never need a coat of paint. Thermal breaks minimize heat transfer between the inner and outer window units.

Rigid vinyl replacement windows may cost less than aluminum units and can be fitted into standard jambs without costly structural changes.

The glass area is the largest portion of either aluminum or PVC windows; thus heat or cold transmission is the same in either unit, assuming the glass installation is identical.

Get comparative prices on aluminum and vinyl window replacements and discuss both the pros and cons with the dealers. The domestic track record on aluminum windows is well established, but that of vinyl is less so. Compare the dollar difference as well as the actual anticipated savings of energy costs between the two types of material. Then make your choice, and you should be satisfied with it. To the real estate editor:

I refer to the recent ''Ask a Builder'' question headlined ''Doing away with the grate can increase the efficiency of a fireplace.'' For years I have been heating our home with the fireplace, burning from three to five cords of wood on the ashes during the heating season. Usually I start the fire sometime in October, and it never goes out until April or May.

One point I have learned, which was not mentioned in the article, is not to pile the logs on top of one another, because they burn faster than necessary for even heat. I lay the logs on the ashes lightly together, so that they burn from the rear toward the front and provide a steady, comfortable heat 24 hours a day without frequent additions of more wood. John G. Rapp Dresden, N.Y.