For the common, one-inch-thick type of residential filter, we recommend that you change it every month. As particles accumulate on the filter, they progressively block the passage of air through the filter. This means your furnace has to work harder to “suck” air through the filter. This can lessen the useful life of your furnace, as well as raise your utility bills. These potential problems are avoided bymonthly filter replacement.
Filters of greater thicknesses (such as four-inch and five-inch filters), which are much less common than one-inch filters, can last longer—some up to a year.