Do power attic fans do a better job of venting the heat out? I have heard some people say they are a waist of money because the motors won't last long running in the heated condition they run in. I have 3 in my attic and all 3 motors are done. I want to replace them with either a higher quality moter or take them out completly and use something else. I live in Tennessee so our arttics here get pretty hot.