When selecting an air conditioner, consider the following three characteristics carefully: the energy efficiency rating, sizing, and the system’s components.

Energy efficiency rating

In the United States, we rate an A/C’s energy efficiency by how many British thermal units (Btu) of heat it moves for each watt-hour of electrical energy it consumes. Every residential air conditioner sold in this country has an EnergyGuide Label, which features the A/C’s heating and cooling efficiency performance rating, comparing it to other available makes and models.

The Heating Seasonal Performance Factor (HSPF) rates both the efficiency of the compressor and the electric-resistance elements. The HSPF gives the number of Btu harvested per watt-hour used. The most efficient A/Cs have an HSPF of between 8 and 10.

The Seasonal Energy Efficiency Ratio (SEER) rates an air conditioner’s cooling efficiency. In general, the higher the SEER, the higher the cost. However, the energy savings can return the higher initial investment several times during the air conditioner’s life. Replacing a 1970s vintage, central heat pump (SEER = 6) with a new unit (SEER=12) will use half the energy to pr ovide the same amount of cooling, cutting air-conditioning costs in half. The most efficient air conditioners have SEERs of between 14 and 18.

You’ll find the Energy Star label sponsored by the U.S Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA) on air conditioners with an HSPF of at least 7 and a SEER of at least 12. Many new air conditioners exceed these ratings, but looking for this label is a good way to start shopping for one.


When selecting a new air conditioner, it’s important that you determine the proper size needed for your home. Bigger is not better. Oversizing causes the air conditioner to start and stop more frequently, which is less efficient and harder on the components than letting it run for longer cycles. A properly sized A/C will also provide you with better comfort and humidity control than an oversized one.The heating and cooling capacity of air conditioners is measured in Btu per hour. The cooling capacity is commonly expressed in “tons” of cooling capacity each ton equaling 12,000 Btu per hour. Correct sizing procedures involve complex calculations, which are best performed by an experienced contractor, who uses sizing methods accepted by the A/C industry. Don’t employ a contractor who guesses the size of the air conditioner needed. Rule-of-thumb sizing techniques are generally inaccurate, often resulting in higher than necessary purchase and annual energy costs.

System components

You and your contractor should discuss options that will help improve your home’s comfort and the economy of your air conditioner. Regarding ducts, for example, it’s important to carefully consider their design and materials, as well as the proper amount of space they require. Check your home’s blueprints to see if the architect and builder have planned adequate space for ducts and fans. Heating and cooling contractors complain that they often have to squeeze heating and cooling systems into spaces that are too small, resulting in constricted ducts and inadequate airflow.Except for packaged systems, you’ll also need to select the proper type of indoor coil for adequate summer moisture removal.