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 . . .

I don't think there's a gas fireplace out there that will heat the large space you have with the heat loss through all that glass unless it's on all day long.

flue blocked can mean a pressure switch not making all the time. Some times the air movement out side can blow into the stack so the pressure switch can't make so it turn off on safety saying, flue blocked. The flame failure can be caused from the same condition from outside. Have they changed or checked the pressure to see at what pressure it will fail. later paulbm

i'm in the same situation. one installer told me the alpine has issues, and national grid will stop selling them in june 09. let's face it, the utility is contracting with burnham to buy trailer loads of boilers for oil to gas swaps, and hi efficiency is really not their goal. you get what you pay for, imho. i'm considering the wm155 ultra, upon recommendation of an installer. however, others, like triangle tube, buderus, veissman may be even better. the whole technology is so new, many installers simply don't have the sweat equity or knowledge. any installer will basically install what you want, as long as they make a sale/money. we're doing our research online, which we have to, and hopefully we can teach ourselves to make a wise choice. i dont think we can make too much of a mistake with any of these new mod/con gas boilers. i'm more concerned with heat loss calculations, and proper sizing and piping of the installation. i'm in blue point, where r u located? have you decided or come close to deciding which installer you will use?