Your air conditioner works hard over the summer. Don't make it work any harder than necessary. Keep the unit running smoothly—and keep cooling costs low—by checking the HVAC filter on a regular basis (as often as once per month if you own pets or live with a smoker). While slightly more expensive washable filters can be reused, cheaper fiberglass filters, once dirty, must be replaced. Consult the manual to learn the recommended filter type for your unit.