Dog pants excessively!?

He is a little over a year old, he's most LIKELY a German Shepard mix, were not completely sure, we've gotten many opinions on it. His fur isn't too thick, sort of medium. His fur is mostly black with so e blonde and a bit of white. He pants constantly. Even in single digit snowy weather. >.< my other doggie never pants as much as he does, not even half as much. I'm very worried i don't think it's bc he's hot, like I said even in single digits panting so I'm worried it may be something medically wrong.