My friends family has a shore house we’ve gone to a few times. It’s an old house, built before a/c was a thing, and still doesn’t have any. We throw open some windows and the house stays pretty comfortable, it’s warm but not at all unbearable even when the temps are in the 80s, 90s, occasionally even over 100 (fahrenheit of course)

It does help that it’s at the shore so there’s basically always a nice breeze.