How often should you change a furnace filter?

Check a furnace filter monthly until you understand how quickly it loads, then replace it according to its condition and the manufacturer guidance. Homes with pets, construction dust, smoke, or many occupants may need more frequent changes. Use the correct size and rating: a very restrictive filter can reduce airflow and contribute to overheating or short cycling. Filter changes do not replace professional safety, combustion, electrical, or airflow checks. If the filter loads unusually fast, ask why instead of simply buying a higher-efficiency filter.