A humidity controlled air flow terminal device works as a humidity sensor : its openingsurface varies according to relative humidity inside a room in order to match air flow rate topollution. These components are fouling up when used during several months.In a laboratory, an air flow with a high rate of particules is fouling up five identical air devicesin a few hours. Considering a constant relative humidity, the impacts on two devices aresimilar : it seems that artificial fouling tests can be reproduced. These first tests show a highsensitivity to fouling at low relative humidities (small openings devices) and nearly nosensitivity at high relative humidities (large openings devices).The characteristic curve of a humidity controlled air flow device represents the air flow rate infunction of the relative humidity at a set pressure loss. The curves of four devices arecompared before and after the accelerated fouling : the most important absolute air flowreduction is about 3.1 11s. This maximum is always reached near the point of RH = 60 %. Thecorresponding relative reduction varies from 14 % to 23 %. The nearly same relativereductions are measured at the point of RH = 60 % with two years old fouled up devices fromreal dwellings although the fouling is visually very different. Thus, the accelerated artificialfouling experiments seem to be representative of real cases.