The AHRI directory contains rated values for air conditioners and heat pumps. These explain how a split system, which is an outdoor unit and an indoor unit, perform as a paired set. This is a more precise measure for the equipment that you are considering for your home. Please click here to see definitions of EER, SEER and HSPF, the most common measures of a units efficiency. Note that the AHRI data include information for all models still being sold, including those currently in production (active) and those which are no longer currently in production but are still available (discontinued).