you dont have to delete anything if you select the duct & bends like in the picture, then just change the diameter in the box at the top left of your screen it will change both duct & fittings

hello
this is exactly what i expected but when i select my duct system (including the fittings) i haven't this case to change the diameter
when i change a diameter of a duct, it changes only one duct and creates duct reducer at the end of my duct (just before the elbow!!!)
do i miss something?
Phil

You should be able to select ducts and fittings and resize, its only duct accessories that dont work like that. Unless you have fittings with fixed sizes? (Diameter as a Type parameter?) Or maybe because you have rectangular and round ducts selected together, so it doesnt show diameter for all?

This is why it pays to model duct systems properly, with flow rates. It costs a bit more time to set the flows in your air terminals and make sure the system is connected, but then its just tab->click->duct/sizing to size everything. Fittings and even duct accesories are all sized in one go.

Otherwise, working with placeholders can speed things up (especially for pipes). No fittings, so if you change the sizes, even in a schedule, you dont get crazy reducers everywhere.

thank you joseph for your comment about rectanguar ducts
that's right that in my last selection i had a dust including round and rectangular ducts so it didn't work
when i select only round ou rectangular ducts (or pipes) it works
Phil