First, the product description air-conditioned rooms with a positive pressure self-hanging Grille auto exhaust. Under normal circumstances vent louvers by weight and drooping naturally, isolated indoor and outdoor air exchange, when the indoor air pressure is greater than the outdoor air pressure, airflow exhaust louvers blowing outward, whereas indoor air pressure is less than the outdoor air pressure, air flow can not reverse flows into the chamber, the outlet one-way non-return effect.