1 CFM/Sq.Ft. of living space, or 1 x 2000 or a total of 2000 CFM of air flow into the total occupied building space. Now divide the total CFM required by 400 CFM (typical air flow per ton of cooling capacity of an air handler) 2000 CFM required / 400 CFM per ton = 5 tons of cooling capacity. You need 5 tons of air conditioning capacity.