is a barometric damper really necessary on the exhaust flue when a power venter is used?? wouldn't pressure changes at the chimney exit almost be eliminated with power venter??
Absolutly required. It's to prevent the power ventor from affecting the operation of the heater.
All power venters have too much capacity when new, so they still need a damper to regulate the draft as time goes on. Build a chimney instead, they work better by far.