Heat normally travels from areas of higher heat to areas of lower heat. For example, if you were to be in a classroom and all the windows and doors were closed, and then you opened a door, then the reason why the room becomes cooler is not because cold air comes inside the room. However, it is because when you open the door, the heat from the classroom you're in escapes the room. This is why it feels cooler when you open a door, or even a window. Heat is traveling from areas of higher heat to areas of lower heat.
Action and reaction are equal in magnitude and opposite direction by they don't balance each other because they don't occur on the same body. Action is involved on one body and reaction is involved on another body.
Hope you understood...
