DEAR SAM: We are contemplating having a new garage door installed. We have heard about a fiberglass door which never needs painting. Could you give me your views about it as compared to a wood door in the matters of durability, insulation (excluding cold), and price?

ANSWER: The fiberglass door would probably be more popular in southern climates, since the factor of insulation in the garage is not serious and the lightness of the door provides easier lifting. The construction of the door of translucent, semi-corrugated panels (1 1/4 inches) which are framed within aluminum boxes of 1 3/8 inches thick, do not require painting and provide a security factor inasmuch as one cannot determine whether a car is parked in the garage.

With reference to other details of comparison, the wood door is more sturdy and provides better insulation, although garages are usually not heated. The brittleness of the fiberglass may involve repairs, since stones or baseballs coming in contact will cause damage to one of the four panels. Finally, the price of the standard 8x7-foot, four-panel overhead door with all necessary hardware, installed in prepared opening is approximately $176 in wood and $217 in fiberglass. During winter shipment, wood doors already given a prime coat of paint, both sides and edges. In most cases, a rubber molding is attached to the base panel which provides an insulating threshold with the garage floor.

Sam Fishlyn welcomes your letters on home improvements and will include as many as possible in this column, which will have a general interest to the readers. Write to him at P.O. Box 62, Newton Centre, Mass. 02159. For a personal reply, be sure to include a self-addressed, stamped envelope.