Can one use 热 and 冷 to describe people?
You may need words of 2 characters, but I'm sure Chinese can do that. Specifically, what do you want to express? Hot or cold: passion, zeal, enthusiasm, interest, love, desire, hate? Here are some pairs of opposites.


热情 —— 冷静
热心 —— 冷淡
热门 —— 冷漠


Furthermore, you can write:   


  他冷冷地对我说了 ...
  我热情地微笑着, ...