Yes from my reading ventilators do provide benefit in winter too.
On that subject, this is interesting
http://www.condorvent.com.au/comparison.html
The guy's theory is that the "whirly-gig" ventilators ar primarily a "winter" device and his inert design works much better in cooling houses in summer -
maybe i bought the wrong thing oh well - might need to try Blknightts "mod" and put a fan in them.

