I thought you only had to change an air filter every month. Well, as it turns out, this is more of a recommendation, rather than a hard and fast rule. It’s more of an average estimate, gauged by the number of people living in the house, the size of the home, and how much cleaning you do. It also depends on the number of pets you have. I live in a very small house, which is perfectly sized for just me and the dogs. However, after I adopted my third dog, I noticed the AC started acting up. I was changing out the filters every month, but when I went to change them they were disgusting. The air conditioning filters were so clogged it was obvious that they were the culprit behind the lagging AC system. They were so bad, I at one point thought I had perhaps been so busy I’d forgotten to change them for a month. However, I always mark the day I swap out the air filter on my calendar. When I looked, I had definitely done it. So I called my HVAC contractor to come down and inspect my system. He found a ton of dog hair and dust in the ductwork. I needed a whole ductwork cleaning. Fortunately, my house is so small that this didn’t cost too much. The AC repair guy was even kind enough to help me avoid needing another ductwork cleaning in the future. I just need to change out my filters every two weeks. I can handle that just fine!