Adding temperatures is not done usually. Mixing substances adds thermal energy. There's no reason I can hink of why allowing plus operator on temperatures is a

Adding temperatures is not done usually. Mixing substances adds thermal energy. There's no reason I can hink of why allowing plus operator on temperatures is a good idea. You can add temperature differentials, but it is plain addition so long as units are in agreement. And 0C differential is 0F differential, no offsets in conversions.