It is our recommendation that you change AC filters once a month when you are leaving your system on all the time, so you will see this task on our list for most, but not all, months. Changing out the AC filters will extend the life of your system, allow it to operate more efficiently, and even help keep the house clean. That’s right - the filters collect dust that would otherwise be spread through the house. It is a good idea to buy a carton of filters at a time. Pay close attention to the direction arrows when installing each filter. We also recommend writing the date on the filters so that you will know at a glance when they were last changed.