I live in southern PA, and it's hot here also.
Both my horses have been sweating for weeks....since they do not have shade in their dry lot, and will NOT use the shade trees in their pasture for some strange reason I cannot understand, they come in from 11 am to 5 pm. Our barn owner just bought them a huge industrial/barn fan that sounds like a helicopter. Lol Both ends of the stable have doors that are the size of a wall and we open them both so each end of the barn is completely open, crank up the barn fan/helicopter.....and they chill for the afternoon, licking their salt licks like popsicles.