Generally, you should change your MERV-rated filter a minimum of once per year; however, you may wish to change it more often. Lifestyle and circumstance can vastly change the frequency of your filter replacement.  For instance, if you have pets, live near a busy highway, smoke, or if you live in a location that has more dust, pollen or similar air particles, you may need to change your filter more frequently. Are you remodeling your home? You might change the air filter more often until your remodeling is complete and the dust has settled. Do you use chemicals in your hobbies? We recommend checking your filter monthly just to be sure.