A large museum storage building whose relative humidity was controlled by warming to reduce relative humidity showed a violently oscillating tempoerature which a period of about a week, as predicted by a computer model. The principle of humidity control by heating a building when the RH drops below the set point does not work in buildings that have a small air exchange rate and are filled with water absorbent materials. Such buildings must be controlled by dehumidification or by heating at constant energy input. -- ICCROM