If you use a company that does the job thoroughly, you only need the ducts cleaned every 3 to 5 years. If you have a home remodel project with a lot of dust, you may want them cleaned sooner. Air ducts should be cleaned every 2 or 3 years if you can afford it. If you are someone who has a lot of Allergies to dust then you might want to consider it sooner. Believe it or not, it is possible to do some of the cleaning youself. Just remove the screens and put your vacuum hose in as far as you can. In addition to that, make sure you always have a clean filter for your furnace.