Envirosept 1224 Disposable Furnace Filters Use these disposable furnace filters for the Envirosept Model EAF-1224 not included are 10 inches by 21 inches. Note the actual size of the Envirosept electronic furnace panel is not 12 x 24 it is 11.5 x 23.5 x 1 . The replacement disposable furnace filters are smaller, 10 x 21 inches. Replace air 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 wherethe 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.