In the past, I've read that they are mostly a gimmick.
I think that a similar "stovepipe" type of structure with
a weather cap would do just as well. Some vertical
height would seemingly let it draw like a flue, as
opposed to the low profile static vents they sell at HD.
I haven't seen any recent tech info on this, though.
Bill

"Zypher" wrote in message
link.net...
I've always wondered if those 'turbine ventilators' really work? Do they
really move that much more from the attic space than say a dormer might?