Always use a fully designed ductwork system – for domestic ventilation this would usually be done by the system supplier, however they may charge for this. Use
the ductwork and fittings specified and don’t allow shortcuts with flexible or shallow plastic ductwork. Cleanliness needs to be maintained during construction.
Any dirt in the ductwork system will be blown into the house later. Keep ductwork covered before use and cover open ends of ductwork during construction. Do not run the fans at all until after the final clean of the house to avoid drawing dust etc into the ductwork.
Commissioning is the job of setting the system up with the correct flowrates. This can only be done once the house is clean. Traditional branched systems need to
have the fl owrate for each room adjusted at the terminal, though good ductwork system design will give required settings (in mm). Semi-rigid systems may come designed with specific flow regulating inserts for the duct to each room. It is still necessary to check the flow at each terminal.
Excerpt from “How to build a Passivhaus: Rules of thumb”, chapter by Alan Clarke, Passivhaus Trust, April 2015.