 It pressurizes the attic and pushes all that hot air out. So it not only cools your house by bringing cool air into the house, but it also cools down that extremely hot attic cavity. I'll bet you if you put a thermometer up there tomorrow when it's over at 100 degrees, I'll bet you that attic gets up to, what, 140? Maybe even more than that up there in the attic. And so by pushing that heat out of there,