I have a cheap zero clearance pre fab fireplace that came with the house. It is a huge piece of junk that wastes so much of my heat and makes the room freezing. I have read that there is no insert that will work in a pre fab fireplace. Is this true? Is there any solution besides spending several thousand to make a masonry chimney? I have seen a few members here who have installed an insert despite the cheap pre fab? Is this a special insert or are they just asking for trouble?