Head over to The Home Depot and snag the Arm & Hammer Enhanced Allergen and Odor Control 4-Pack Air Filters Just $19.99! (regularly $39.99) This deal is valid today only, January 25th. Choose from a variety of sizes to fit most furnaces. Keeping a clean filter is crucial to getting optimal performance from your furnace. These also qualify for free delivery. It that is not available in your area, you can select free in-store pick up to avoid shipping fees.