One of the biggest concerns when deciding on which type and model of heating and air-conditiong unit you wish to purchase is the efficiency rating. The modern heating and air-conditioning units have become extremely cost effective to run. You can use the below graph to translate the SEER rating (the efficiency rating) into dollars and cents. For example, replacing a unit with a SEER rating of a 7 with a SEER 12 should reduce your operating costs by half!