Product review (5 stars): Not  only  recommended  but  absolutely  necessary
worked  fine,  costs  only  a  fraction  of  the  Rheem  part.  I  don't  understand  why  Home Depot  or  Lowes  does  not  carry  it -  they  sell  gas water heaters  and they  sell  vent  pipes  but  not  this  essential  part. Without  this  part  carbon monoxide  could  enter  the  house.