"The Oven"

In order to alleviate these overcrowded conditions, on June 1, 1801, President Thomas Jefferson approved the board of commissioners' plan to build a temporary chamber on the foundations of the south wing that had been constructed between 1793-1796. The temporary chamber within the north wing would no longer be large enough for the additional new members that would be added following the 1800 census.

Congress then signed a $4,789 contract on June 20, 1801, to build a temporary chamber for the House of Representatives. Following the contract award, the building was hastily constructed as an elliptical room with poor ventilation. At times, members of Congress missed votes due to the "suffocating feeling of the air in the Hall." It earned the nickname "the Oven."

From the website of the Architect of the Capitol - https://www.aoc.gov/blog/constructing-capitol-oven