The ordinary window shade doesn't have much of a reputation as an energy-saving device. Still, the typical shade can cut down on winter heat loss through a window by as much as 20 or 25 percent. That's not bad for a simple item that costs only about $8.

Even so, you can get performance significantly better that by making some simple changes in the shade and in the way it's mounted.

Here's one of the simplest: When it comes to blocking heat loss, a shade performs best when spaced out about half an inch from its window. But most shades are mounted so they come off the front of the roller, and that spaces the shade well in front of its window.

You can reduce that spacing by reversing the shade so that it unrolls from the back of the roller. To do this, remove the shade -- roller and all -- from its mount. These will be simple metal brackets nailed or screwed to the window frame. Remove these brackets and replace them in opposite positions. Put the left one where the right one was and vice-versa. Then simply turn the shade end for end and replace it in the mounts. It will now unroll off its rear surface.

The shade will now fit closer to the window, and this will cut down somewhat on air circulation behind the shade. This in turn will cut down on heat loss by another 5 percent or so, and won't cost you a cent.

Another trick is to add a single layer of aluminized plastic to your shade. Aluminized films are made in a variety of types, but one of the cheapest and most available is the "Rescue Blanket," a sheet of aluminized vinyl measuring 56 by 84 inches. It is sold at many sporting goods stores, or you can buy it mail order from L.L. Bean, Freeport, Maine 04033, for around $3.

To add aluminized film to a shade, first unroll the shade and remove the existing shade material. This will usually be stapled in place. Next, cut the metalized film to the same size as the old shade material. Then place the old fabric and the metalized film together -- metalized surface facing the old fabric -- and staple them both onto the shade roller.

From inside your home, the shade will look just like the old shade, but it will have a layer of metalized film in it that can further reduce heat loss through your window to about 45 percent.

You can increase the effectiveness of the shade even further by using a double layer of metalized film looped around a dowel. Cut the dowel to about half an inch shorter than the width of its shade. Simply place it inside the looped film. Do not glue it in place. If left free to roll within the loop, it will do a better job of keeping the two layers of film tight and wrinkle-free.

Multiple layers of metalized film like this are the insulting principle used in space suits. A shade of this type can be quite effective, cutting heat loss by well over 50 percent if installed on a tight, draft-free window.

These are some of the simpler ways of cutting heat loss through windows. If you would like to learn more about this subject, a pair of new books will interest you. One is "moveable Insulation," by William K. Langdon. Rodale Press. The other is "Thermal Shutters and Shades," by William A. Shurcliff, Brick House Publishing. Both are abailable at bookstores.