1 If the floor or area near the furnace is a dust-bunny breeding area, vacuum or sweep prior to replacing the filter.
2 Locate the service panel, usually on the furnace's lower front or side.
3 Turn off the furnace, then gently pop open or pull down the panel door with your hands; tools usually aren't needed.
4 Locate the filter--a framed-mesh rectangular screen inserted either horizontally or vertically near the intake-outtake blower.
5 Slide the filter screen out (see A).
6 Check for brown, dusty buildup on the mesh screen (or a screen you're unable to see through).
7 If you have a reusable plastic-frame or metal-frame filter, use a hose to rinse away the dust particles on the screen in the backyard or driveway (see B). Let it dry, then return it to the furnace.
8 If you have a disposable cardboard-frame filter, write down the size, then throw it away. Buy a new furnace filter of the same size