Residential central air-conditioning systems with high seasonal energy efficiency ratio (SEER) ratings have become available in recent years from multiple manufacturers. In the common split system configuration, the top SEERs available from the major unitary air conditioning system manufacturers now range between 18 and 24.5 Btu/Wh across the 2 ton to 5 ton (7 kW to 17.6 kW) range of residential cooling capacities. Improvements in compressor, fan and expansion valve technologies, along with generous coil sizing, have enabled significant gains in SEER rating.