The frequency in which an air filter should be changed depends upon your HVAC system and your preferences. The primary recommendation is to change the filter once a month when the system is being used regularly. It’s a good idea to pick a date each month and set a calendar reminder for yourself to change the filter. You can also check to see if the air filter needs to be changed by holding it up to a light source. If you can’t see through the filter, it’s time for a clean replacement.