i use my bonus room as my snakeroom and i keep it at 78 to 82 all year long and keep my heat tape on but i have my rats up there too and if its too hot they will not breed, but i think if i was just my snakes up there ill keep the heat higher and turn everything off in the summer.
When i lived in MI i had to keep my heat tape on all year because it never got really warm in the summer .