The National Trust for Historic Preservation chose the Unico System to keep visitors comfortable in this 19th-century Washington, D.C., row house. You don't recognize the place? This is where Abraham Lincoln died. He was carried here, to the Petersen House, after being shot in Ford's Theater across the street. Today, the building serves as a museum, with the Unico System providing all-season comfort through ducts that snake behind walls and underneath flooring.