Most furnaces use disposable filters; you just throw them away and buy replacements. But some filters are actually designed to be washed and reused, time and time again. These "permanent," washable filters have metal housings rather than the flimsy cardboard that surrounds disposable filters. Energy Star recommends that you check your furnace filter monthly. Clean it every three months at a minimum, according to the American Lung Association.
Set the dirty filter down onto the floor with the dirty side facing up; try to avoid dumping debris.
Plug in your vacuum cleaner and turn it on. Carefully vacuum the filter to pick up as much dust and debris as possible. Turn off the vacuum.
Pick up the filter and carry it to a large utility sink or bathtub.
Turn on the faucet and rinse the filter thoroughly in warm running water. If you have a sprayer attached to your faucet, this is best, as it allows greater water pressure. Rub the filter with your hands or a soft brush to help wash away any remaining debris. Do not use soap. Turn off the faucet.
Allow the filter to fully dry before returning it to the furnace.