http://www.epa.gov/iaq/pubs/airduct.html
I am sure that you prob already checked this out. It kind of gives some guidelines for consumers. It also says that some kind of vacuum system is the best. I know my company uses a ToraVac system. I think that that is a name brand not really sure. I have looked the net for them and found different kinds depending on how big you want to go.
I personall think that is a good money maker. People are concerned about health these days and even though that website says that there is no proof about health affects,we have had people write letters to our company saying that there allergies and asthema symptoms have been reduced greatly. Well anyways good luck.