One of the most important things to remember about your furnace filter (regardless
of the MERV rating) is that keeping a clean, unclogged filter in your furnace or AC will ensure that your unit will run at maximum efficiency while also keeping the air in your home as clean as possible. In addition, replacing your filter frequently will also protect your unit from unnecessary and untimely repair costs. While there are certain variables that determine the specific replacement frequency required for your filter (such as overall running time on the unit, the type of flooring in the house, and the presence of pets), it is important to keep in mind that most filters should be replaced at least every three months for optimal performance while filters with a higher MERV rating (12 or 13) will likely need to be changed even more frequently.