the period of time, the sidereal day, during which the earth makes one complete revolution on its axis relative to a particular star. The mean sidereal day lasts 23 hours 56 minutes 4.1 seconds of the mean solar day.
In this corner: a vent stack is series of vertical pipe vents that passes through at least two stories and is meant to maintain atmospheric pressure in the drainage system. The vent stack usually runs parallel with the soil/waste stack and may either extend up through the roof or connect to a stack vent. And in this corner: a stack vent is the uppermost portion of a soil/waste stack that continues the pipe from above the highest connected fixture out the roof.
automatic vent damper. . The typical automatic vent damper is an electrically controlled flap that sits in the vent connector, just downstream (after) of the draft hood (draft diverter). It's just a fancy sock to stop air leaking up the chimney when the furnace is off. There are also heat activated vent dampers, but these are less common.