The powered fan will suck some intake air from the ridge vent..from the closest, easiest air supply. If you block the ridge, it may suck conditioned air from below, even back-drafting gas appliances (worse case). I feel if you cut power but leave it in place, the gables and ridge will act as exhaust if they are located more than 3' above the soffit (intake) vents. http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/bpn/57_e.pdf
http://en.allexperts.com/q/Roofing-1598/Ridge-Gable-Vents.htm
http://www.nachi.org/attic-ventilation-systems-part1-25.htm
http://www.advancedenergy.org/build...entilation/Attic Ventilation Case Studies.pdf
Gary
http://en.allexperts.com/q/Roofing-1598/Ridge-Gable-Vents.htm
http://www.nachi.org/attic-ventilation-systems-part1-25.htm
http://www.advancedenergy.org/build...entilation/Attic Ventilation Case Studies.pdf
Gary