Air is drawn through the openings, down the house, and out the fans, like a wind tunnel. This form of ventilation is popular in hot climates to provide additional summer ventilation, quickly removing heat and excess moisture. A smooth high air speed at bird level of 2 to 3 m/s lowers the temperature perceived by the birds (wind-chill factor). In winter or when tunnel ventilation is not required, the large insulated inlet flaps close reliably to prevent temperature loss.