Each section of ductwork in Design Master HVAC is sized independently when using the constant pressure drop or constant velocity calculation methods. This can result in a main duct run changing size at every duct branch.
It is possible to prevent this by using the “Same as Previous” setting on the ducts.
To do this, use the “DM HVAC->Ductwork Centerlines->Query Duct” command. Select the duct that you what to have the same size as the one previous to it. In this case, we selected the three red ducts.
Set the “Same As Previous” toggle to be on. Ducts that have this set will be drawn to match the size of the duct previous to it.