Ah, the roaring fire, holding back the cold and drawing family and friends around it. Here's how to start it, preserve the heat and save the chimney.

Fatwood, a highly resinous pine that contains a dense concentration of pitch, makes an excellent starter for your fall fire (don't use it to replace the firewood itself). Timber Resources offers packages of fatwood called Lightnin's Sticks, long enough to lay on the grate lengthwise. Or chop a fatwood stick into thirds and insert the pieces into your firewood. A 12-pound carton is $ 19.50 (add $ 2.50 for postage and handling). Timber Resources, Earlysville, Va. 22936 (804/973-5268).

A black, fire-resistant fiberglass fireplace curtain ($ 16.95 from New England Hardwood Firewood Co., Little City Rd., Higganum, Conn. 06441. 203/347-3648) seals off the fireplace when you leave the house or go to bed. The curtain comes in one size, 43 by 33 inches -- tailor it to your fireplace opening with scissors. Hooks attach it to a wire mesh screen. Sparks can't fly through the curtain during its die-down stage, and the fireplace won't draw heated air up the flue.

A fireplace that previously functioned well may be blocked with creosote buildup. You can clean the chimney yourself using brushes (Acme Stove Co., 1011 7th St. NW, 628-8952, has a rod kit of several sizes at $ 29.95). It's safer to hire a chimney sweep (about $ 50) who will use wire bristle brooms and brushes, and should chip away caked-on creosote with long-handled tools -- vacuuming equipment alone will not loosen it. Have your chimney cleaned once a year if you use it five or six times a week, every three years if you use it once or twice a week. Santa will thank you.