How often should you change your furnace filter?

A dirty furnace filter doesn’t just make your air dusty—it forces your HVAC system to work harder, which raises your energy bill and shortens the life of the equipment. The replacement interval depends on the filter type and your household.

Thin 1-inch fiberglass filters are the cheapest but clog fastest: swap them every 30 days. A 1-inch pleated filter traps more particles and typically lasts 30 to 90 days. If you upgraded to a 4-inch media filter (the kind in a dedicated cabinet near the furnace), you’re looking at every six to 12 months.

These are baselines. Shorten the interval to every 30–60 days if you have a dog or cat (pet dander clogs filters fast), someone in the house has allergies or asthma, or your system runs nearly nonstop during a hot summer or cold winter. The simplest test: hold the filter up to a light. If you can’t see light through it, it’s overdue regardless of the calendar.

A reliable furnace filter is a small investment that makes this easier: furnace filter.