12 Furnace Filters for Envirosept 2024 Keep your furnace air purifier working. Buy this pack of 12 EnviroSept air filter collector pads for Envirosept Furnace Panel HVAC air purifier model 2024 Furnace Panel NOT included . Actual pad size is 18 x 21 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 panelinto slot and plug in. This item ships from a separate warehouse and may require extra time for delivery.