There are three performance factors to consider when purchasing an exhaust fan for a tunnel-ventilated poultry house: air moving capacity, energy efficiency, and air flow ratio. Knowing the air moving capacity of an exhaust fan, at a static pressure of 0.05", helps a grower to determine how many fans his house will require. For instance, let's say a grower is going to build a 40' X 500' dropped ceiling (7 1/2' side wall) broiler house. To obtain the desired air exchange rate and air speed he w...ill need to have a minimum of 170,000 cfm of exhaust fan capacity. If a fan he was considering purchasing moved 19,000 cfm at a static pressure of 0.05", he would need to purchase nine fans. If the fan moved 23,000 cfm, approximately eight fans would be required.