Your air filter should be replaced every three months or 90 days. This will ensure the filter is clean enough to capture any dirt and contaminants, keeping them out of the system. Your HVAC technician should replace your air filter when during your maintenance appointments, but you’ll need to remember to do it for the rest of the year. We suggest making a reminder on your calendar, so you don’t forget. You can usually pick up replacement filters at your local hardware store and changing them is a simple as taking out the old filter and replacing it with the new.