I have done 4 story buildings before. If your system is straight up and down or minimal bends or have access panels to system I don't see a problem. If your system has round tubes it still can be cleaned back to bare metal. Would need to talk about the system more. A six story building would most likely take one day to complete and have it down to bare metal. If interested in paying me to come down and do it I would be willing to do that. I have a 2 man crew and insurance also references.. I would love to spend some time in New York City. I am in New Hampshire Please contact me if interested at 603-493-6437
THANK YOU BOB