12 Furnace Filters for Envirosept 1220 Disposable furnace filters for the Envirosept Model EAF-1220 not included are 10 inches by 17 inches. Note the actual size of the Envirosept electronic furnace panel is not 12 x 20 it is 11.5 x 19 1/2 x 1 . The replacement disposable furnace filters are smaller, 10 x 17 inches. Replace filter pads monthly or more often if your home or business requires it. Note Measure the panel insert including the black plastic piece to get accurate dimensions of your Envirosept insert. Replacement furnace filter pads cover only the inside mesh part of the furnace air cleaner panel. Replacement furnace filters are made from a custom polywool blend of proprietary fibers without latex or adhesives. We suggest a label on your furnace to remind you of the size. To Replace Furnace Filters Unplug the unit. Remove furnace filter panel from the slot. Open the two retaining clips. Remove both filters. If desired, move the less dirty filter to where the dirtier filter was. Add second filter. Push the clips closed, slide panel into slot and plug in. This item ships from a separate warehouse and may require extra time for delivery.