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 . . .

We have a new home (supposedy Energy Star) that was built in 2007. We have a direct vent gas fireplace in the outside wall of our family room. This is where we spend all of our time as it is an open concept home. In the winter the floor and surrounding room is unbearably cold. We need to keep the fireplace on in order to keep the room warm and the floor bearable (even if thermostat is set at 21 celcius 24 hours a day). The problem with that is that when we put the kids to bed, their rooms are freezing because the fireplace being on trips the thermostat. I decided to place a thermometer on the floor in front of the unit to see how cold it actually was and it very quickly showed us 1.5 degrees celcius!!!!!!! Somehow, I doubt this is normal! We have had the builder in MANY times and they have even pulled the roof off our outside chase and stuck in some more insulation. They try and tell us that it is normal for cold air to come in from the fireplace because it is vented to the outside and any amount of wind will enter...I honestly have no idea how this home even passed the Energy Star testing because we are always freezing!!!! Any suggestions of how to approach this one? The builder doesn't send anyone of any experience and we are at a complete loss...Thanks!!

Use the owners manual that came with your DV unit to determine venting configurations, then your local code enforcement authority, but for the heck of it what do you mean exactly? You want to run the pipe out the back of the box, then through the wall, then 8' away from the house and just have it hanging out there? I don't quite understand.

TL;DR at bottom I recently resealed the flue joint on my Direct Vent Gas Fireplace with 600F Red silicone sealant. I noted that the same material was used to affix the fiberglass gasket around the glass front of the fireplace and concluded that the red silicone would be safe to use on the flue gasket. Over the summer I had disconnected the flue vent from the fireplace so I could attach the AC exhaust to it, there were no windows nearby in my tiny apartment to properly run the AC exhaust. I noticed a fiberglass ring type gasket that was glued to both the top of the fireplace and the underside of the flue joint on the vent pipe with red silicone sealant. The gasket basically disintegrated when I removed the pipe, thus the reason for needing to reseal the joint now. I had previously used 2000F stove cement on the joint but it cracked and flaked off quickly and I was worried about leakage. I applied the red silicone both as a ring between the flue joint and the top of the fireplace and as a caulk line around the edges of the joint. The first time I turned on the fireplace everything seemed fine, though I didn't run it for too long. The second time, after about 10 minutes or so I noticed a growing smell of hot plastic, I looked inside the top with a flashlight and saw small wisps of smoke rising from the exterior of the flue pipe. The top of the fireplace itself was sizzling hot to the touch, instantly vapourizing the layer of saliva I'd put on my finger to test it. However the silicone was fine, not soft or bubbling, and cool enough to touch for a few seconds. I even removed a small piece of cured silicone and heated it up over my stove to compare the odour, I noticed that the silicone did not release any odour until it went past its temperature threshold and began to turn brown, then it smelled more like burning pitch than plastic. I'm fairly confident that it's not the silicone that's causing the odour and perhaps is just some dust or lint from synthetic fabrics that's gathered on my fireplace while it was off for 7 months. Though I vacuumed the top when I was doing its fall cleaning before turning it back on, there seems to be a lot of really stuck on fine particulate still there. TL;DR Used 600F red silicone sealant to seal joint between flue pipe and gas fireplace, hot plastic smell present when first run, suspect it was the sealant but testing seemed to suggest that the odour was not from the sealant. Was the 600F silicone the correct choice for the flue joint? Please advise, thanks! Photo of my sealant job after the fireplace was run for 15 minutes is attached - I may have been a bit heavy handed with the caulking gun, it was an awkward space to get the gun into and ended up just having to squeeze clumps on my finger and spread it that way. Thanks!