If your chickens seem to be stressing from the heat, the best thing for them is air circulation. I've done some research on this subject because I know that chickens can get stressed from the heat and die - and it gets hot, hot, hot here. I researched on several university sights and the consensus was that air circulation is the best way to keep your birds cool. I know it works, because when mine start to get stressed (excess panting, etc.) I turn on box fans in their coops (my coops consist of 3-sided buildings with attached runs) and soak the dirt in front of the fans, and it really works. It's still hot, but the air movement allows the chickens to get rid of excess body heat, so they don't stress. I also checked into what the poultry operations around here do to keep their birds cool, and they all use huge fans to circulate the air in their buildings. I remember reading somewhere that misters aren't a good idea because when the chicken's feathers are damp, it actually holds the heat in. I can't find where I read that, so I don't know what site it was on, nor can I go back and evaluate the source, but it makes sense.