When winter snows blanket the Vermont countryside and ambient temperatures hover around zero degrees F., or even below, Charlie Hall frequently gives himself a special treat: He relaxes in the steaming waters of a Jacuzzi in a room that is bathed by the warming rays of the sun.
What makes this unusual is that his bathroom is situated on the cold side of the house - farthest from the sun along the north wall. A foreshortened interior wall separating the south-facing living room from the bathroom, coupled with a large mirror on the rear wall, does the trick.
The low-angled winter sun pours into the Hall home, heating the large masonry wall (heat sink) at the rear of the living room. This masonry wall does not reach the ceiling, however, so that some of the sun's rays pass over the wall and into the bathroom immediately behind it. The mirror on the north wall then directs the rays into the tub.
Meanwhile the masonry wall also radiates some of its stored heat into the bathroom, making for a very ''comfortable experience'' even when the mercury drops below zero.
As Mr. Hall explains it: ''We get the comfort of the subtropics in there in the middle of winter.'' In summer the higher angle of the sun prevents any rays reaching the room.