I have a small 2 story house that many years ago was moved from a cement foundation and set right on the ground. The sills and stringers have rotted and must be replaced. I am digging out a crall space underneith. The water line and trap for the shower is insulated. I live in the north where it gets very cold in the winter months. The floor of the house is not insulated and there has never been a freeze up of the pipes. I suspect because it was on the dirt and the cold couldnot penatrate. I am going to use heat tapes on the lines and am planning on ventaliting the crall space. Is this a good idea and would it be ok to close off the vents in the winter time?