A furnace uses a blower fan to suck in air from around your home and then move this air past a heat exchanger before it enters your home. As it sucks in air, the blower fan could also bring in large particles that would damage the furnace. That’s why you have an air filter.
You probably know that there is an air filter in the furnace that you are supposed to change every month or so. And we hope you do—neglecting to change the filter can cause clogs that restrict airflow, overworking your furnace, reducing efficiency, and eventually leading to repair issues.