Changing or cleaning furnace filters protects the furnace, air conditioner, or heat pump from dirt and maximizes the energy efficiency of your furnace, air conditioner or heat pump. Your filter protects the blower, heating coils, and cooling coils from dirt. If these heating components get dirty, they are difficult and expensive to clean. Changing the filters in your furnace, air conditioner, or heat pump is one of the most important home energy conservation and maintenance tasks. When filters get plugged with dirt, airflow through the ducts is reduced and your air conditioner’s performance and efficiency suffer. You should change or clean your filter every 2 to 4 months when you are air conditioning or heating. The fiberglass filters in the cardboard frames are disposable. The filters made of plastic fibers, usually blue in color, are washable in soap and water.
Before you can change a filter, you have to know where it is. Your filter is located in the return grill, in the main return near the furnace, or inside the furnace near the blower. If you can’t find your filter, contact your air-conditioning contractor.
Many homes have electronic air cleaners or other filters that are designed to collect dust for health reasons. These filters need even more attention than the standard filters because they get dirty quicker. Electronic air cleaners are usually cleaned by removing their core and metal pre-filter and washing them in the automatic dishwasher or with a hose outside. Clean or replace other specialty filters according to the manufacturer’s instructions packaged with the filter.
See The Homeowners Handbook to Energy Efficiency or Residential Energy: Cost Savings and Comfort for Existing Buildings Chapter 6 for more information. For professional information about heating systems and energy efficiency see Saturn Hydronic Systems Field Guide.
Here is an article for further Furnace Filter Maintenance information.