I think I may be missing something fundamental here. In imperial units. How do you know when you can do a straight conversion from psi to ft like this A fan operates at a temperature of 70F and a pressure of 1 atm. The fan moves air at 3000 ft/min against a static pressure of 0.02 psig through a 2 ft diameter duct. The fan speed is increased by 30%, whereas the air properties remain the same. The horsepower delivered to the air by the fan is most nearly Answers 2.5 hp 3.1 hp 3.6 hp 4.2 hp