Probalby get shot for saying this but we got Aiden McCarra 087 6847415 to install all our duct work. Its in and looks good. If you are getting ducting, get the metal pipes as the plastic are prone to ripping plus more of a fire hazard. don't let anyone tell you otherwise!!
He works in conjunction with Kingspan, I think. An engineer recommended him to us. It is the heating system company that commission the work of the units, which we got approval of so I am sure that they checked the ducting but basically if we have any problems when we turn the heating system which is related to the ducting, we can just give him a call.