I know the Duct Pressure Loss feature of Revit 2017 is still underdeveloped. However, I am wondering if anyone knows if there is a certain dimension relationship requirement between the rectangular dimensions of a takeoff fitting for a branch and the dimensions of a main duct. For example, the takeoff fitting of 10"x18" branch will correctly link to an ASHRAE table if I connect that branch into a 18"x20" main duct. However, if I now try to connect the 10"x18" branch into a 22"x18" main duct, the fitting will no longer link to an ASHRAE table.
My question is: are there certain dimensional relationships required between branches and main ducts for takeoff fittings to successfully link to ASHRAE? I have tried many different dimension configurations between branches and ducts and I do not see any logical pattern.
