Heat itself won't hurt the leaves. Ask anyone who has grown in the desert SW and we'll tell you heat is not a problem as long as the roots are kept cool. Light and sun burns don't usually begin on the edges either but start where the light hits at the highest angle so burn spots appear in the middle of the leaves most often. Burnt, crispy edges are more often than not an overfeeding/overwatering problem so I'll have to agree with Crazyhorse here on this one.