Art, if you do go through the wall, make certain that horizontal section has some rise to it. 1/4" per foot minimum but 1/2" per foot of horizontal is much better as it will improve the draft a lot. You also have to remember that the height of the chimney will effectively decrease by 2-3' with each 90 degree elbow and this is one more good point for going straight up. Having said that, our chimney is through the wall then up the side. We have no problem with it.
