The Courtauld Institute Galleries moved to a renovated 18th-century building in 1990. Financial constraints and shortage of space had prevented the installation of a conventional air- conditioning system. Initially, the large number of visitors caused a steep rise in temperature, relative humidity, and carbon dioxide levels in the unventilated rooms. The solution, which was finally agreed upon, combined ventilation through the old chimneys, and dispersed humidifiers and dehumidifiers linked together by computer control, which improved the climate in the building. This approach increased visitor comfort by reducing carbon dioxide levels, and improved environmental stability for the paintings through better control of humidity. -- CAL