The cost of replacing a whole HVAC unit ranges from $5,000 to $10,000, with the nationwide average being $7,000. This equates to between $25 to $60 per square foot. Prices are determined by the size and manufacturer of the HVAC system, the size of the house, the length of the ductwork, and the efficiency rating of the new unit. Expect to pay between $1,500 to $12,500 for new installations. HVAC installation expenses generally range between $500 and $2,500 in labor costs. The entire cost is determined by the kind and state of the existing system.