space least-although with the addition of insulation, the protection afforded by a crawl space or slab is greatly improved.

An attic or crawl area above a dwelling helps prevent heat from escaping. An attached garage may afford some protection on one side of a house but, of course, is a heavy energy user in those uncommon instances when heated.

The larger the home, the more energy it uses, all other things being equal. The organization of space within the home can also make a difference. For example, a two-story house of 1,500 square feet has about 20 to 25 percent less exposed surface than a one-story house with the same floor area. Because it has less exposed surface, the two-story house also would use 20 to 25 percent less energy for heating.

The type of heating system makes a difference. All other things being equal, an electrically heated home requires about twice as much fuel per unit of heat as a gas or oil heated home. The presence of at least one thermostat or radiator valve is important in order to permit the family to control room temperature. More than one thermostat or valve is helpful, especially in large homes, permitting room temperatures to vary according to use.

The openings in a building, such as doors and windows, are places for heat to escape in the winter or to enter in the summer. The type of window also makes a difference. The most common type of window—double hung—is the most energy conserving. Casement and sliding windows are less energy conserving since they have more crevices and leaking areas for hot or cold air to move in or out. Wood frames provide better protection than metal; double glazed (thermopane) glass more protection than conventional (single glazed) glass. The larger the window, the more heat is likely to be lost. Storm windows, storm doors, and weatherstripping can reduce heat loss. (The relation of energy to dollar savings from storm windows is discussed later.)

Most of these structural characteristics that affect energy use are determined at the time of construction and may be impossible or at least difficult and expensive to change. This is true of square feet of floor space; size, shape, and number of windows and doors; degree of insulation; and type of roof and foundation. It is particularly true if the household lives in rented quarters, especially in an apartment.