We had ours cleaned last fall. The guy that did it said you don't need to do this again unless you do construction in your house, mainly drywalling anything. They don't get that dirty with regular daily life as long as you use a filter on your furnace. Most people don't have them cleaned after they build or if you are in an older home, they just have never been done. It does cut down on the amount of dust you have in your house.