A Company Called Energy Star estimates, that the retail price and installation of a 5-ton central air conditioner is at more than $1,700. That’s not very cheap at all, but these systems need to be replaced about once every 10 to 12 years. To qualify for the Stimulus plan for home, central air conditioners need a seasonal energy efficiency ratio, or a SEER, which will measures the efficiency of central air, of at least 16 and an energy efficiency rating, or a EER, which will track how it operates once the outdoor temperature reaches around 95 degrees, of at least 13.