Why and How to Change Filters

Dirty filters kill your AC's efficiency, so install a new one every month during the cooling season for central and window units (or clean them if you've got the washable type). Look for the filter's minimum efficiency reporting value, or MERV, which ranges from 1 to 12 for home AC units; the higher the number, the better filtration it provides (and the more energy needed to pull air through it, so balance air-quality concerns with energy costs).