I had always thought you only had to change an air filter every week. Well, as it turns out, this is more of a recommendation, instead of a difficult 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 also how much cleaning you do. It also depends on the number of pets you have. I live in a rather small house, which is very well sized for just me plus the dogs that I have. With that being said, after I adopted my second dog from a shelter, I noticed the A/C started acting up out of nowhere. I was adjusting out the filters every week, however when I went to change them they were disgusting, but the a/c filters were so stuffed up that it was evident that they were the culprit behind the lagging A/C system. They were so terrible, I at a single point thought I had perhaps been so stressed I’d forgotten to change them for a week. With that being said, I pretty much always mark the day I swap out the air filter on my calendar. When I looked, I had truly done it, and so I called my Heating plus A/C company to come down plus inspect my unit. She discovered a ton of dog hair plus dust in the air duct. I needed a whole air duct cleaning, but fortunately, my residence is so small that this didn’t cost too much. The A/C repair woman was even kind enough to help me avoid needing another air duct cleaning in the future. I just need to change out my filters every two weeks. I can handle that just fine!