Ahhh the cold snap is here. I grow in an attic and the room requires additional heat in the winter months(more than just the lights). Cannabis can survive at pretty amazingly cold temps. That is survive, not flourish, not even grow at all if too cold, just sit there and hang on.
You wanna grow nice nugs in your garage room you WILL have to buy and use a heater, period.
Environment(temp, RH) the single most important factors in indoor growing. Get the environ right and then and only then will your room really start producing nicely for you.