I think that it DOES put stresses on the motor to slow the fan down with a rheostat. I have heard that myself and the sound that my motor gave off, when I did it, sounded bad. Probably would just shorten the lifespan of the motor. But those motors last quite a while. Why not just attach your fan to a piggyback thermostat? It will turn itself on/off as needed. I guess this will not take care of the volume when it is on though, huh?