If he likes Cal Poly SLO, he probably would like Chico a lot. Both schools have the same “vibe”. The heat shouldn’t be that big of an issue, because students usually go home for the summer before it gets super hot. The only really hot times for a student are the first few weeks of school, and by then, the days are a bit shorter, so the heat doesn’t last as long.
I wouldn’t worry too much about Chico’s rep as a party school. Even when I went there in the Stone Age, there were plenty of things for non-partying kids to do. My local Chico friends have told me that the current University administration is working hard to get rid of the party school rep, too. If you haven’t been up to Chico, I encourage you to go up and take a look.