John in Thunder Bay has moved his gas burning fireplace from the centre of the house and he is moving it to the side of the basement and wants to run it up the outside of the house. He was asking if there could be any problem with downdrafting by doing this. The answer is that this is the worst change you could make to a chimney. If at all possible put the chimney inside the thermal insulation of the house. If you must run a prefabricated chimney up the side of the house, build a box around it (respecting fire clearances required by the manufacturer) and insulate the box on three sides, but not on the house side. In fact it would be better if it were possible to remove the insulation from the wall on the house side, so that the thermal envelope of the house jogged right around this chimney, keeping it warm when it is not burning and when it is barely burning. That way, the warm air of the house will keep a slight continual up-draft in this chimney and you won't have problems starting the fire.
For a good graphic and more information check out "Poor Draft up a Fireplace Chimney".