Between 1840 and 1846 the Scottish physician David Boswell Reid produced a scheme for a central ventilation system serving the Palace of Westminster. This scheme included a proposal for a sophisticated ventilation and climatic control system in the House of Commons. Although the plans for a central system were abandoned after six years, Reid was able to implement his idea within the confines of the House of Commons. Existing literature on Reid’s involvement in the design of the Palace of Westminster has focused largely on his difficult relationship with the architect Charles Barry, but his actual contribution to the design of the ventilation system has remained largely unexplored. Neither his unfinished early proposal nor his final design for the House of Commons has been studied in any depth before. This paper retraces the evolution of Reid’s original plans, and provides a systematic reconstruction of the ventilation system implemented inside the House of Commons between 1847 and 1854. The historic system is now completely lost, but new archival research, involving the study of several hundred letters, sketches and plans, has yielded detailed insights into its design and how it performed historically. In addition to revealing the ventilation system’s physical arrangements, research has uncovered how scientists and engineers had evaluated its design empirically from a human and technological perspective. As such, this paper provides a new perspective on antiquarian studies and illuminates how architectural technology in the mid-nineteenth century was shaped, evaluated and refined based on environmental performance. Although environmental factors, such as climate or air purity, were more transient dimensions of architecture, in the case of the House of Commons this paper shows that they were key drivers of architectural form.