It's foolish to run your car in the garage for extended lentghs of time with the garage door closed, but the law has taken steps to protect people from themselves...
sadly in my experience here in the montreal area there is a hell of a lot of houses in the montreal area built pre 1970 with forced air heat that have a return AND heat duct in the garage. My usual recomendation for these is seal them and install a pair of electric baseboards set to +/- 12c
