Here in the desert farming community its safe to say we have dust. And regardless of how clean you keep your home, dust still gets into the ducts. Depending on your needs, you should have them professionally cleaned out every 3-10 years.
The number one best time to clean out your ducts is when ever you're replacing your furnace or air conditioner. The biggest killer of equipment is dirt, and the last thing you want to do is turn your new system on, only to have it suck a bunch of old dirt through it.The second best time is right after a remodel, or construction work. Remember, dirt is not a friend to your heating and cooling system.
I've had duct cleaning part of my business almost from the beginning, and through some expensive trial and error, I now have a system for cleaning most ducts, second to none. I have a 25 hp gas powered vacuum that sits outside from which I run a 10 inch suction tube to your furnace, and duct system. It has enough suction to collapse your duct work. I then run a high pressure (175 psi) air tool down each duct knocking everything loose, and pushing it towards the vacuum, leaving no mess behind in the home. All dirt is sucked outside.
The process takes from 3 to 5 hours depending on the home, and system. At the same time I thoroughly clean out your furnace, and service it. I also clean your indoor air conditioner coil. I also can clean out your drier vent at the same time, or all by itself. Please call me if you have any questions.