HVAC question- The term "stack" for ductwork?

Question

Does it refer to all ductwork other than the odds & end pieces such as elbows, diffusers, etc?

Answer 1

Normally the "stack" or riser is a portion of the duct work the  that is installed vertically, usually between floors, such as a flue in a "chimney stack".

Answer 2

The term stack is used (Thermal stack).heat rises, cold drops so if you're trying to blow cold air up stairs the thermal stack is going to work against you. friction loss is the term used to figure the drag on the air going thru the pipe and around the elbows and ect.

Answer 3

The stack I believe is going to be the duct work that feeds the branches either between floors or the main trunk.