How to replace your air conditioner

How much efficiency is enough?

Air-conditioning units are graded on the SEER scale, which stands for seasonal energy efficiency ratio. The higher the number, the more efficient the unit.

The lowest rating allowed for units sold in the U.S. is 13. The highest rating is 30.

Most efficient units hit the mid- to high 20s.

Air-conditioning systems must have a SEER rating of at least 14 to be considered for the Energy Star program.

The Washington, D.C.-based American Council for an Energy Efficient Economy recommends units with at least a SEER rating of 14.5-15.0 if you live in a warm climate.

Energy Star units can cost an additional $300 to $2,000 more than comparable conventional models, depending on the size of the unit your house needs. In all, you can expect to pay several thousand dollars for a typical replacement unit, according to Consumer Reports.

For that additional up-front cash, you'll save money on your energy bills, up to $200 annually depending on where you live, according to the U.S. Department of Energy.