Residential HVAC Installation Practice Exam

The component in the cfm calculation formula that represents the air changes per hour is ACH, or air changes per hour. This is because ACH specifically measures the number of times the entire volume of air within a space is replaced in one hour. Option B, volume of the house, is incorrect because while it is an important aspect in the cfm calculation formula, it does not solely represent the air changes per hour. Options C and D, rate of air leakage and time duration in minutes, are also incorrect as they do not account for the entire volume of air within the space and do not specifically measure the number of times it is replaced in one hour.