Q: Do the various types of heat-saver grates, which are now so widely used in many fireplaces, cool the air going up the chimney so much that there will be problems with deposits of combustible material accumulating on the inside of the chimney lining? I've heard that stovepipes can accumulate enough creosote to create a hazard, but is this also true of a chimney in a fire-place?

A: I doubt if any of the heat-saver grates you ask about could cause this kind of problem. They do take a little heat out of the fire, and out of the air going up the chimney, but the degree of cooling involved is not enough to create the kind of problem you are referring to. Build-ups can occur from other things - very green wood, not enough draft, and the like - but not from installing one of these onvection type grates.

Q: About 15 years ago I had a chain link fence installed around my backyard. Now it is rusted and needs painting. Should the rust be removed first, and if so, how can this be done? Also, is a metal primer necessary?

A: I definitely advise removing most of the rust. You can do this effectively with a wire brush - scraping is impractical. Various types of brushes are sold for use in electric drills. This is faster than wire-brushing by hand, but be sure to wear goggles to protect your eyes. After the rust is off, apply a good coat of metal primer (Such as one containing zinc chromate), and be sure to paint all sides of the wire mesh. The best way is by spraying, but the job can also be done efficiently with a deep pile roller. Either way, work from both sides to insure complete coverage. Then finish with two coats of outdoor trim paint in the color of your choice. This too can be applied by spray or with a roller - both are faster than brushing.

Q: I have a fieldstone fireplace in my house that has been in use for years. The stones above the firebox have blackened with soot. Short of sandblasting, how can the soot be removed from the stones?

A: Scrubbing with a strong detergent solution and a stiff brush will usually remove most of it. If you want to go further, you can try to wash it off with a muriatic acid solution. Mix one part acid with three parts water (the acid is sold in most paint and hardware stores), then scrub this on and let it stand until it stops bubbling (about 10 minutes). Then flush off with plenty of water. Wear rubber gloves to protect your hands, goggles to protect your eyes, and mix in a plastic or porcelain container, not metal.

Q: I applied a coat of wax to my polyurethane floor and it is now so slippery that it is unsafe. Is there some special wax I should have used to prevent this?

A: There is no special wax that can be used to insure against a slippery floor - most waxes are slippery to some degree. However, it should not be dangerously so. Chances are you either put too much wax on (it should be applied in very thin layers or coats), or you did not buff it enough after you put it down (it is best to buff floor wax with a machine - unless it is the kind that does not need buffing).

Questions about home repair problems should be addressed to Home Improvement Department, The New York Times, 229 W. 43d St., New York, N.Y. 10036. Questions of general interest will be answered, but unpublished letters will not be answered individually.