Keeping Rooms are small and the purpose is for people to enjoy the fire while someone cooks. They are also not large enough to be a stand alone room.
Fireplace– All of these spaces should have a heat source, such as a fireplace. This is the key element for all of these rooms.
Sitting area– In order to enjoy the fire and keep warm, the space must have some form of seating.
Bookshelves– Not all of them have bookshelves, but many modern keeping rooms do.