Keeping Congress Cool for the Summer

With summer in full swing, and the weather in Washington, D.C., becoming hotter and more humid, it's the responsibility of the Architect of the Capitol (AOC) to ensure that it's cool enough inside the Capitol for Congress to continue its work.

During the Capitol expansion in the 1850s, large wooden fans were installed in the basement to circulate fresh air into the House Chamber through vents throughout the room. In 1871, as a result of legislation to improve the removal of "vitiated air," the AOC expanded the exhaust ventilating shaft and rebuilt the chamber floor to relocate the vents.

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Drawing for a fan room signed “MC MEIGS, CAPT. OF ENGINEERS,” 1858; One of the last operating steam-powered fans in the U.S. Capitol, ca. 1911.

Some Members noticed an improvement, but by 1873, the House was again debating how to improve ventilation. Many Members continued to chafe against the chamber's location in the center of the building, with no windows that could be opened for access to "the air and the light of heaven." This group wanted to expand the chamber by removing the offices between it and the exterior wall, but others thought expanding the hall would be like holding sessions in a "ten-acre field."

Before making the structural changes that removing offices would require, the House created an advisory board. After studying the situation, the board recommended less drastic alterations. The most extensive changes were to the rooms around the chamber, removing doors, walls, and a fireplace to create unobstructed airflow from the windows in those rooms into the House Chamber.

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Image Drawings of registers and a ventilator for the House Chamber during the 1850s extension.

Although repeated analyses showed that the ventilation system was well designed and properly operated, Members continued to believe that the air quality could be improved. In 1895, a frustrated Massachusetts representative opined that New England jails and prisons were better ventilated than the House Chamber. In response, defenders of the Architect of the Capitol sampled air from various buildings in the Bay State and proved that congressional air was as pure as that breathed by Massachusetts school children.

When Congress worked throughout a long, hot summer in 1890, the AOC provided electric fans and bought 1,000 feet of rough boards to hold blocks of ice to cool the Senate Chamber.

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Heating and venitlating details for the north (Senate) wing of the U.S. Capitol Extension during the 1850s.

Senators had also complained about the lack of access to windows in their chamber. In 1924, the Senate directed the Architect of the Capitol to consult with reputable architects to improve the "living conditions of the Senate Chamber" with an unstated goal of moving the chamber to abut an exterior wall. Plans were drawn up, but before work could start, in 1927, a commission of experts advised the Architect on a new form of ventilation called "air conditioning."

Funds were easily secured to install air conditioning in both the House and Senate Chambers, and work was completed by August 1929. This ended the campaigns to move the House and Senate Chambers, as well as the complaints about the quality of the air.

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Teams of AOC employees, including mechanics, insulators, instrumentation controls technicians and other HVAC experts, work on temperature control.

In 1935, Congress appropriated money to provide the rest of the Capitol and the office buildings with this new form of ventilation. Central refrigeration equipment was installed at the Capitol Power Plant.

Today, the Architect of the Capitol continues to provide air conditioning with chilled water from the Capitol Power Plant coursing through underground tunnels and miles of pipes across the campus, ensuring that Congress can continue working comfortably, no matter the weather.