Hi Shane, As was already stated, some garages are connected to the house, with a door leading from the house directly into the garage.
In most cases, one might want to provide as much insulation from the cold as possible in order to avoid any drafts that may be present from the garage to the house interior. In some cases, the garage may be heated along with the rest of the house, so to have air coming in through the garage door, just makes for a cash cow. Another item you may want to consider, is that the more heat you can draw out of the garage, the better it is for the car, and allowing for easier starts in the winter. I just watched a movie called The Day After Tomorrow, where North America was subjected to a flash freeze, which rendered a helicopter to freeze as soon as it hit. The motor on the copter froze solid, and the thing started to spin instead of the actual blades. While I'm not saying this will happen to a car anytime soon, in places like Alaska and Northern Canada, temperatures can go down quite substantially, and then it becomes quite difficult to start a car in those conditions. Suffice it to say, the more protection you place on your car from environmental influences, the better it is for the car. Victor
