Filters. How many? I think about five in my vacuum cleaner. All of them get blocked up. So when you come to clean them out you have to clear each one. Having long hair and cats doesn’t help. Our old cleaner was a lot more efficient and needed less maintenance. I guess the twists and turns dust has to follow through the machine, causes the blockages, like blood clots in a branching venous system. Not to mention… Hubby’s socks that get left in odd places and cause more problems! Argh!