A typical furnace filter consists of many interwoven fibers layered in random directions. When looking for a replacement filter, you’ll likely come across the words “MERV” and “HEPA”. If you’re like most homeowners, you’ll assume that the one with the higher number equals better protection against foreign elements. While this may be true in most cases, this type of filter isn’t always ideal for your home, depending on what type of HVAC system you have.