Many of us were taught that a dry, hot nose was a sure sign our dog was sick and that a wet, cool nose was a sign of health. In fact, your dog's nose may change from wet and cool, to dry and hot from one minute to the next in the course of the day, based on environment (temperature, humidity, etc.).
The most important gauge of illness is how your dog behaves. Does he have a good appetite, is he full of energy and wants to play?
If your dog acts sick and has a hot dry nose, check with your veterinarian.