We describe the adjustment and calibration of thermistor anemometers. These devices are suited to the range 0.05 to 0.5 m/s, and affected by experimental errors between 5 x 10(-3) and 2 x 10(-2) m/s. Their main advantage is a good handiness as well as a low price which make it possible to perform in situ measurements at a large number of points simultaneously. For these reasons, they represent an ideal device for the measurement of velocity fields in closed spaces and especially for the study of convective movements in buildings.