My dog is a bear, and he is always panting. At first he thought it was very hot, but now it's not hot and he's still breathing like this.
The hair on a dog is equivalent to a man's cotton-padded coat. Dogs have their mouths and tongues sticking out when walking, running and walking except at rest. It's not that he is panting, but that he wants to breathe and radiate heat through his mouth, because dogs have no other radiating organs except his mouth, so don't worry if they are cold.