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.
An air filter’s minimum efficiency reporting value (MERV) rating measures how effectively the filter stops dust and other contaminants from passing through the filter and into the air stream. Filters with higher MERV ratings trap small particles more effectively than filters with lower MERV ratings. In general, filters with a rating of MERV 16 or below are considered to be HVAC-system-grade filters for residential, commercial and general hospital use. MERV 17 through MERV 20 filters are typically used in surgical operating rooms, clean rooms and other contexts that require absolute cleanliness.
When selecting the right filter for your application, higher is not always better. Using an air filter with a MERV rating higher than what your furnace or air conditioner manufacturer recommends can actually impair its performance. The smaller pores in more highly rated air filters create resistance to air flow, and if the filter is used in an HVAC system that is not designed to handle this resistance, it can lower the system’s efficiency, decrease indoor air quality, and put strain on the system’s fan.
Generally, most air filter manufacturers and HVAC companies recommend changing your air filter every 90 days, or 3 months. That can change based on where your home is located (ex. dusty, dry climates), if you have any pets, and the age of your system and equipment. If you have pets in the home, you should consider changing your filter every 60 days, or 2 months, and for homes with multiple pets or people with allergies or respiratory conditions, we recommend changing your filter every 20-45 days. Vacation homes or vacant homes that don’t see much use can typically wait to change out filters every 9-12 months. The general consensus is, the more you use your home, the more you need to change your air filter.