For this you need to calculate the kitchen area. For example, if your kitchen is 10*12 with a ceiling height of 10 feet then 10*12*10 = 1200 cubic feet or 34 cubic meter. Let’s say if the air while cooking has to be cleaned 15 times in an hour then the calculation is 34*15=510 which is minimum suction power you require. But if you cook meat or deep fry regularly then the suction power has to be even more than that.