20 times per h have stove room air change times, 30 to 40 times per h. Air change times = room air supply volume / room volume, the unit is times / hour. The size of the number of air changes is not only related to the nature of the air-conditioned room, but also with the volume of the room, height, location, air supply and the degree of indoor air deterioration and many other factors, is an empirical coefficient.