If a fan tries to push 6" of airflow through a 4" reducer it will and I must exemplify the word will, reduce the life of the fan. It is proper physics. However, does a 6" fan really push the CFM to overfill a 4"? That can be debated.
If a fan tries to push 6" of airflow through a 4" reducer it will and I must exemplify the word will, reduce the life of the fan. It is proper physics. However, does a 6" fan really push the CFM to overfill a 4"? That can be debated.
Mine is dummed down to a 4" dryer vent.
It still works fine. 90's and other bends can be more restrictive than shrinking diameter, smooth wall tubing is best.