To prevent 75 percent of a building's total air loss, seal subtle leaks. Seal electrical outlets and gaps between moldings, as well as plumbing and wiring penetrations. In the attic, pay particular attention to hatches, plumbing vents, chimneys, and other roof or wall penetrations. In smaller areas, use a caulk gun and several tubes of silicones or urethane caulking. In larger areas, use foam sealants. Outlet plugs and foam pads installed behind outlet and switch covers are wise investments, particularly in campus-like building complexes in colder climates.