Run a roto-brush through a five year old peice of flex, typical of brach supply connections and then look at the inside of the flex! If it isn't completely destroyed, it will be damanged.
Then run it through a peice of hard pipe, and then wipe the pipe with white cloth. You'll find substantial debris on the cloth.
Using peunmatic systems you will much better results and less damage to flex. However, your also looking at a lot more money for a system that will actually do some cleaning. From what I have seen truck or trailer mount systems are the way to go. Forget the roto-brush.
This is personal opinion from personal observation.
ya i agree i used the rotobrush for about 5 years before i started doing heatin and cooling and that rotobrush is junk don't buy it get a negative air type like the abatement hepa-aire it is a way better machine and does alot better job
Things I have learned over the last 10 years about air duct cleaning.
1. It is a multi-billion dollar industry
2. All major studies have shown it does not reduce indoor particle counts
3. There are no studies that show it has any positive effect on allergies. All claims are anecdotal and probably have to do with the amount of money spent.
4. If the coil is not cleaned, duct cleaning is totally worthless. In many states the only people who can open up a system and clean the coil are licensed HVAC contractors.
5. Anything using a stiff brush around flex duct is a bad idea.
6. Any homeowner could vacuum out at least 90% of what is obtained by air duct cleaning by using their vacuum on the first several feet of the returns and the last 18 inches of the supplies.
7. If dirt has been in the duct for 10 to 20 years, it is not going anywhere. It is happy right where it is - unless someone comes by and messes with it by "cleaning" the duct.
8. There are two cases where I recommend air duct cleaning - 1. when there is clear evidence that the HVAC system has been contaminated with mold and 2. where there has been remodeling done in a house and the contractors have not sealed the HVAC system. (you can wind up with some pretty nasty "white" dust)
The short answer on air duct cleaning is: when in doubt, don't do it.