Air filters are typically made from spun fiberglass (the same thing that makes up your attic insulation) or pleated paper & framed with cardboard for stability and rigidity. They are inserted into a specific place within your return air duct (usually a large drop down vent in your hallway or other place in your home). These air filters act as barriers to prevent contaminants from entering your HVAC system or circulating within the air. Most filters are designed to block out dust, dirt, pet hair, lint, mold, bacteria, and more. Air filters typically have a MERV (minimum efficiency reporting value) that determines the type and size of pollutants the filter will work against.
Air filters can last between six months and three years depending on the quality of construction used and how much usage they receive while they are installed in your home. The lifespan of an air filter depends largely upon its design – some filters are more effective than others at filtering out certain contaminants while others may not be as effective at filtering out certain types of particulate matter (PM).
It's important to remember that these filters are not designed to trap all contaminants. They are only meant to block out the things that you have already identified are a problem for you and your family.
If you have allergies, dust mites, dust, mold spores and other irritants can still get into your home through other means like your doors and windows. These air filters are designed to trap airborne particles that can enter your HVAC system while keeping out larger particles like dirt, pet hair and lint.
If you have pets, they shed fur that can contain allergens such as dander (dead skin cells), saliva and dead skin cells which can be carried into your home on pet hair.
If you're looking for an inexpensive way to improve indoor air quality without investing too much money into upgrading your HVAC system then consider installing an air filter today!