Product review (5 stars): Perfect for bathroom vents
Although I found this item on AMAZON, I did not buy it through AMAZON as the roofing company that installed them had them in stock.  I recently upgraded bathroom exhausts in upper level bathrooms and had 2 of these vents installed through the roof.  I had them installed professionally as my roof is too high and steep for me to get onto.  I live in Indiana, and we recently had 14 inches of snow and temperatures in the negative 20's (the high temperatures were sub-zero for several days!).  These vents worked perfectly- they were not impeded by the snow on the roof, the back-check valves did not freeze shut, and the warm air they exhausted did not cause ice dams. I am very happy with these vents and highly recommend them.