Dustless is not the same as dust free, you can expect to see a small amount of dust on horizontal surfaces in the immediate areas being sanded, it will be limited to that area and not throughout the whole house. The dust will not build up on walls and other vertical surfaces. Also to put things into perspective a typical 500 sq ft room refinish would yield about 30-40 gallons of saw dust through the entire sanding process. The dustless system Ann Arbor Hardwoods uses will take care of 99.9% of the dust created.   The system is a Diamond Jet 1200 dustless system which is manufactured specifically for hardwood sanding. The System is H.E.P.A. certified and is certified for lead safe paint removal.