Air filters remove pollen, dust and other particles that would otherwise circulate indoors. Most filters are typically rectangular in shape and about 20 inches by 16 inches, and about 1 inch thick. They slide into the main ductwork near the inside fan unit. The filter should be periodically washed or replaced, depending on the manufacturer’s instructions. A dirty air filter will not only degrade indoor air quality, but it will also strain the motor to work harder to move air through it, increasing energy costs and reducing energy efficiency. The filter should be replaced monthly during heavy use during the cooling seasons. You may need to change the filter more often if the air conditioner is in constant use, if building occupants have respiratory problems,if  you have pets with fur, or if dusty conditions are present.