How Long Do Furnace Filters Last?

Frequency

• Factors that affect how often you need to change your furnace filter include the number of people who live in your house, the number of smokers and whether you have pets. If you have pollen-bearing trees or plants in the area, dirty duct work, or if there are construction or sanding projects in the house, your filter will need more frequent changing. Inspect the filter every month and change it when needed. Your filter might need to be changed every month, or it might go 90 days before it needs to be replaced. Most homeowners need to change their filter three or four times a year.

Testing

• You can tell when the filter needs changing by taking it out of the duct work and holding it up to the sunlight. If you can easily see light shining through the filter, it doesn’t need to be changed. If not, you need to put a new filter in. There are several types to choose from.

Types

• Filters range from inexpensive, disposable fiberglass filters that are capable of removing only large dust particles to HEPA air filters that can remove more than 97 percent of the allergens found in most homes. Fiberglass filters cost as little as $1 each in 2011. Washable filters consisting of a flat metal or plastic pad can last three to five years, and should be cleaned every month. Pleated polyester filters come in a wide range of efficiencies and could have a permanent electrostatic charge that attracts small particles. These filters usually last about three months. You can purchase washable filters for as little as $15 and pleated polyester filters for around $5. Mechanical air filters capable of removing tree pollen are also available, but they require special installation because they don’t fit into standard filter holders. They cost $30 to $40 and last one to two years. Electronic filters cost as much as $500, but they can remove particles as small as smoke. Electronic filters are reusable and need to be cleaned every month.

Choosing

• Inexpensive fiberglass filters remove pet hair and large pieces of dust, but smaller particles pass through them. They protect your furnace, but they don’t remove allergens. Allergen filters can cause problems with some furnace duct systems and damage your furnace. They need to be replaced more often because they clog more quickly. Research by Canada Housing and Mortgage Corporation found that the furnace filter has only a moderate effect on the amount of breathable particles someone in the house is exposed to, and furnace fan filters are effective only if you run the fan all the time.