If your system is old (over 20 years), inefficient (your energy bills are higher than they should be), or need a significant repair, complete system replacement may be the best route to go. Today’s systems are up to 60% more efficient than those of even 10 years ago. Once you start saving on your utility bills, a new unit may create a desirable return on your investment. The savings each month may offset the cost of financing a new system.