Replacement Furnace Filters for EAF-1824 Replacement EnviroSept air filter collector pads for Envirosept Furnace Panel HVAC air purifier model EAF-1824 Panel NOT included . Exact size of each pad is 16 inches by 21.0 inches. The size of the exact filter insert of the Envirosept Model 1824 is 17.5 x 23.5 inches x 1 inch. Use two replacement pads for each filter change unless you remove the dirtier pad and replace it with the cleaner one. 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 theslot. 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.