Wood fuel?

Can you bump the wall out a bit and then run it vertically to get above ground? I don't know your layout but I've built with these twice and it was a while ago but we had an angled vent and I think you can go pretty far in varying directions without a power vent.

You only can run 20' horizontal which is the problem. We are actually above ground (full walkout basement) but if we run to the side we vent right outside french doors and onto a porch which has a masonry patio above. There is a box bay for the guest bedroom immediately to the side so we can't go there. We are just a little too far away to run straight back over the guest bedroom because of 6" stud walls and 3" or so of brick . . .

My builder is getting conflicting reports from fireplace salespeople about whether a b vent will work. The Isokern folks say theirs will, but the fireplace store says all the ones we have found (which frankly seem to have similar venting requirements to the isokern but just cost less) won't work. The isokern salesperson is saying something about how their system has less heat or something? I can't find anything about that and frankly it concerns me because the other fireplace store's technical guru is finding problems with the b vent installation . . .