If you really concerned, only 2 choices: do it yourself, or pay a many times higher prices to hire a company that has a moving robot with a brush to clean the level duct(s); but even these companys can't deal with the vertical/turning pipes.
I did it myself (using a central vaccum). It's very hard to get a shining clean surface even when you brush it. Those guys will usually connect a "powerful" huge pipe to the duct, and tap the duct while vaccuming for a while. I'll be surprised if that helps (as I said, open and see for yourself, for someone who has done it).
I did it myself (using a central vaccum). It's very hard to get a shining clean surface even when you brush it. Those guys will usually connect a "powerful" huge pipe to the duct, and tap the duct while vaccuming for a while. I'll be surprised if that helps (as I said, open and see for yourself, for someone who has done it).