The easiest way to take care of your furnace is to replace the air filter regularly! Home Depot is featuring the Arm & Hammer Odor Allergen and Pet Dander Control Air Filter 12-packs for just $54.45! (regularly $99.99) That is just $4.53 per filter! It is recommended to change your filter at least every 90 days. That means this 12-pack will last you three years, assuming you only have one furnace. This super low price is valid today only, February 21st. Plus, it will qualify for free delivery!