Product review (5 stars): Heartland 21000 Dryer Vent Closure
The Heartland 21000 Dryer Vent Closure has made a noticable difference in temperature of our utility room during the winter.  It is excellent.  While it appears to be a bit light in construction, it functions well and mounts to a brick wall in a very sturdy manner.  Be prepared to provide your own 4" aluminum vent tube, which is an inexpensive item at your local hardware store.  The bottom line is that this item does a good job and is well worth installing.  You can't say that about many products these days.  Thumbs up!!!