Maggie Pattenaude, a western Massachusetts resident, expects to save in the region of 200 gallons of home heating oil this season. That's because she has learned "to TAP the sun's heat," as she is wont to put it.

To be exact, the mother of five has had four 3-by-7-foot thermosyphoning air panels (TAPs, for short) attached to the south wall of the home, and every minute the sun shines these silent workers pump oil-free heat into her home. The TAPs syphon cool air off the floor, heat it up, and by natural convection pump it back in near the ceiling.

Many of us know searingly hot a metal roof becomes on a summer day. If that roof were covered by glass to protect it from direct contact with the cold air, it would become equally hot on a bitingly cold winter day. Well, that principle , along with the fact that hot air rises and cooler air tumbles to the floor, is the secret of the TAPs success.

In brief a TAP is a piece of corrugated metal roofing, painted black for maximum heat absorption, and placed an inch behind a sheet of clear glass, or better still a double- glazed thermopane. This whole panel is then mounted 2 to 3 inches away from a south-facing wall of the home and enclosed in a frame of wood. Two air vents are cut in the wall of the house immediately behind the TAP -- one at the base of the panel, the other at the top. The recommended size for such vents is 8 by 14 inches. The air between the metal and the wall becomes very hot whenever the sun shines; rises as it expands with heat; and exits into the room through the top vent. At the same time, heavier cool air, off the floor, is sucked into the TAP through the lower vent, in turn to the heated up and returned to the house.

After the sun goes down, the registered on the two vents must be closed or the reverse will happen: Warm air will be sucked in through the top vent and cold air displaced back into the room through the lower vent. During summer, of course, the registers can be left open at nights so that the TAP can aircondition the house. During the day in summer a vent at or near the top of the TAP must be left open so that the hot air can escape outdoors.

The Cooperative Extension Service of the United States Department of agriculture states that anyone with "basic carpentry $200 -- the cost of materials. With hired help the cost would naturally be higher.

Experts point out that before erecting a TAP or other heat-collecting unit, it is important first to weatherize and insulate your home. That done, the next point to consider is whether you have enough unshaded south-facing wall space on which to hang one or more TAPs. It may mean, as at Mrs. Pattenaude's home, that a tree has to be removed. Remember, too, that the wall does not have to face directly south for the TAP to be effective; southwest or southeast will do.

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