The furnace filter helps keep the coils and heat exchanges on your HVAC unit clean. When the exchanges and coils become dirty, your system has to work harder, which can shorten its lifespan. The air quality in your home can also decline, which can lead to an increase in asthma and allergy symptoms.
The one inch thick filters made of fiberglass that are found in most furnaces should be replaced approximately every three months. You may need to do this more often if you have pets or children living in the home since they generate more airborne particles. If you have a 4 to 5-inch filter with a Minimum Efficiency Reporting Value rating of 8 to 11, you can get by with replacing your filter once a year or semi-annually if you have children or pets in the home. If you live in a new home, are in the process of remodeling, or have family members with allergies or asthma, you should be especially diligent about changing your furnace filter.