I live in a very hot and humid area, our summers are horribly hot and they last forever. I have 25 chickens of different ages, there are fans in their coops and runs, they have shady places and plenty of waterers, my girls (and one boy) like to dust bathe in the sand on the run, I dampen it slightly every morning and they really enjoy their sand bathing. the deeper the sand the better because even though the sand is in the covered run, the surface is still warm so they dig in deep to bring the cooler sand up.
I also give them electrolytes twice a week, I know they add salt to them but the minerals and vitamins content helps with the stress the heat produces. I know it helps because they used not to eat much and were sort of catatonic on the hottest hours of the day and now they are more active and they eat their normal feed ration.