This is a difficult question to answer. Since every environment and every filter is different, it is very difficult to put an accurate estimate on how long the filters will last. The easiest way to tell when the filters need to be changed is to simply look up. Our filters will get visibly dirty signaling that it is time to replace them. We have seen filters last only 2 weeks in some especially dirty environments, while they can survive many months in very clean settings. If the filters develop a darker color, it is best to change them. Leaving dirty filters in for too long could potential damage your system so it is best to check them regularly.