My Husky x Cody pants as you described all the time. In the house, even in winter, she will lay on her bed and pant. She has a very thick coat and detests the heat! Her preferred napping spot is a pile of snow! As was mentioned, even though the house doesn't feel overly warn to us, it must to her. She just started blowing her coat and usually she pants less with her summer coat. As long as Docker is healthy in all other respects, I wouldn't be too concerned, unless he pants on mild exertion, appears to be overly distressed/lethargic, not eating, drinking, pooping and peeing normally. I'm sure Glacier will give you some great advice!