I was wondering how everyone on here addressed sealing bathroom vents, HRV vents, and other penetrations when they are not in use. I have been looking into electrically opening and spring closed dampers, to really seal up the vents when not in use.

 http://www.rockler.com/product.cfm?page=20047&filter=duct%20damper

I have designed a simple circuit to let the right vents open for exaust and another one for make up air. How do you all address this issue?