In general, paper or fiberglass furnace filters should be replaced either monthly or every two months. Depending on circumstances, electrostatic or HEPA filters should be cleaned or changed every two to four months.
A filter needs to be changed when it is noticeably dusty or when excessive dust is noticed in the home. Filters need to be replaced more often in homes with smokers or pets. Fiberglass filters with cardboard frames are the least expensive option and are designed to be replaced every one or two months. Pleated paper filters are also disposable but last between four months and a year. Reusable electrostatic filters do not need to be replaced, but they require periodic cleaning.