The classical architecture of Washington, D.C., has received much historical attention, but little attention has been paid to the mechanical systems that made these buildings habitable in the capital city's notoriously hot and humid summer climate. In Air-Conditioning Comes to the Nation's Capital, 1928–60, Joseph M. Siry describes how comfort air-conditioning first appeared in the U.S. Capitol building, in the chambers of the House of Representatives and the Senate, in 1928–29. From the 1930s on, air-conditioning systems were extended to the whole of the Capitol, the Senate and House office buildings, the Federal Triangle, and beyond. All of these projects involved the integration of equipment for heating, ventilating, and cooling into the spatial and structural forms of these mostly classical buildings. Air-conditioning had major implications for the annual operations of Congress and the efficiency of federal workplaces. This account advances the historiography of mechanical systems in modern architecture.