How energy efficient is your air conditioning system? The air conditioner air filter in your heating and air conditioning system protect it so that it doesn't work harder than it needs to resulting in wasted energy and money. Air filters prevent dust from accumulating which would otherwise block the airflow through your system resulting in your system being overtaxed. While there’s no set time-frame to clean or replace your air filter, the best answer is to do it as often as is needed. And really, the only way to know how often this should be done is to check your filters periodically until you know the amount of time it takes for your filter to get dirty. Typically, twice a year is a good idea.