DEAR MR. MELTZER: I am planning to put storm windows and screens on my house. I was wondering what the best time of year is to do this. Do the companies offer a special discount for off-season work? I think storm windows will really help my heating bills next winter.

ANSWER: Usually it does not make very much difference. Many storm window companies are not in business during the summer. They start in the fall, and only manufacture in the winter months.

However, there is one factor that may be significant in 1977. It seems as if Congress may pass a law permitting an income tax credit for installation of storm windows. By putting on storm windows this year, you will be able to reduce your income tax bill. This has not yet become a law.

DEAR MR. MELTZER: We recently bought a 10-year-old house. It's in grand condition, and we are loving it.

However, one of the rooms has a terrazzo floor - something we've never had before. We're not so sure about how to keep it clean. We don't want to put anything on it that will either discolor it or mar it in any way.

Do you have any hints for cleaning?

ANSWER: A terrazzo floor is not hard to maintain. Simply sweep with a soft broom. You should mop it from time to time with plain water or with light suds composed of a mild synthetic detergent. Don't use soap, as it will leave a scum on the flooring.

If you wax, use a self-polishing type rather than a polishing wax, which is more slippery. But what you should remember NOT to use is a lacquer or a varnish. They will discolor it.

DEAR MR. MELTZER: Last Christmas my husband gave me a beautiful electric coffee maker. The coffee was great at first, but has recently begun to taste terrible. How come?

ANSWER: It sounds to me as though you're not cleaning your coffee maker as meticulously as you could. If the coffee was great in the beginning, it should still be great.

When a coffee pot is not ket extremely clean, the oil that remains in the coffee maker can become rancid and make the coffee taste bitter. Wash all the parts carefully with suds and rinse thoroughly in hot water. Using a percolator brush, clean the spouts and tubes carefully about once a week.

DEAR MR. MELTZER: My mother and dad were great parents, but very old fashioned, so when I was married it seemed right to me that the house was in my husband's name. But now I wonder what would happen to the house if my husband died suddenly. He has no will.

ANSWER: If your husband dies without a will, it's possible that you may find yourself one of several heirs with a claim against your husband's estate (which includes the house). It would depend upon the interstate laws of the state wherein you reside.

It would simplify matters if your husband would prepare a deed transferring ownership of the house to both of you. The charge for preparing a new deed would be small. There would also be a nominal charge for affidavits and for recording the deed.

I think you should urge your husband to do this.

DEAR MR. MELTZER: Is it cheaper to rent an apartment or to own a house?!

ANSWER: In the short run it is cheaper to rent. In the long run it is cheaper to buy.

There are two reasons why monthly housing costs are higher than rents. It costs less to build an apartment unit.

Costs for operating and maintaining an apartment unit are less than costs frc operating and maintaining a house.

There is the factor, though, that a homeowner gets back a portion of his monthly output in the form of mortgage reduction. In the first years of homeownership, equity growth through mortgage reduction is small. It becomes large in later years.

A homeowner also has income tax advantages which a person who rents does not. In the long run, homeownership is more economical.

DEAR MR. MELTZER: When we bought our house three years ago, we selected the most expensive wallpaers - not because we planned it that way, but because we seem to have that kind of taste.

Well, now we're concerned because it's soiled. There are even spots in places. We were told when we selected it that it was definitely washable wallpaper. But how to wash it is something that we're worried about.

Can you give us some tips?

ANSWER: Even if you were told that your wallpaper is washable it is best to test it in an inconspicuous area first. Using a sponge, dip it in lukewarm water and squeeze until almost dry. Rub very lightly on the paper.If it doesn't blur, start from the bottom and work up.

Wash a small area at a time, but don't rub. Pat dry with a soft, dry cloth.

Grease spots should be removed as quickly as possible. Mix fuller's earth, French chalk and cleaning fluid to make a paste. Smooth directly over the spot and allow it to dry. Then brush it off. If it is a bad spot, it may need two or three applications.

Light smudges can be removed with art gum. Food stains should be brushed off, and then use a cleaning fluid lightly.

Bernard C. Meltzer is a realtor, engineer and appraiser. He does not answer letters personally but only through this column. His address is Suite 900, 112 S. 16th St., Philadelphia, Pa. 19102.