Chimney chase question
用户-6833011| Posted inEnergy Efficiency and Durabilityon
我有一个90年代的房屋，沿着金属烟道管的外墙在外墙上进行了框架追逐。它是在密苏里州圣路易斯，夏季炎热/潮湿的冬季。冬季不使用时，壁炉在冬季冻结，因为只有追逐的前面（内部）壁是绝缘的。
I’m preparing to convert from a wood burning insert to a gas fireplace and have a chance to rectify some of the energy and comfort issues while the front wall of the chase is torn out.
Questions:
a.) Should I insulate the front wall of the chase or just the 3 exterior facing walls?
b。）我只能将其隔离到石膏板顶部（firestop）。如何隔离顶部？我是否应该在现有的干墙燃烧机和另一层干墙之间将矿物羊毛夹在烟道周围的1英寸间隙之间？我会用高温填缝剂空气密封烟道在原始顶部通过的金属项圈。
c.) Where should the vapor barrier go? It’s currently behind the drywall on the insulated interior wall.
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答复
In order:
a。）隔离和空气密封仅仅是外墙，这将烟道追逐在条件空间内完全。
b.) The 1" clearance to B-vent is only to combustibles. Rock wool is not combustible (less combustible than the B-vent itself) and thus needs no clearance, whereas paper-facers on gypsum board are combustible, thus the need for a flanged metal collar for sealing that annular ring. The top side air barrier can also be drywall (with clearance.)
c。）牛皮纸面孔不是一个真正的蒸气屏障 - 它是一种“智能”蒸气延迟器，干燥时约0.5个perms，但是当腔体中的水分含量达到支持霉菌生长的水平时，蒸气会变得相当蒸气。在4区的气候中，当使用牛皮纸面对的烤面包时，将其放在组件的内侧稍好一些。在4A区中，不需要或渴望真正的蒸气屏障，例如4-6 mil聚乙烯，但空气紧密程度很重要。在气候下，蒸气屏障造成的问题要比他们解决的更多问题。使内部空气屏障干墙上涂有至少一层标准内部乳胶底漆，以使其蒸气渗透率下降到约5个摄入量左右。如果/必要时，这将使外部护套朝内部干燥。如果是带有木材，纤维水泥或乙烯基壁板的木鞘墙，则可以搭配“蒸气屏障乳胶”底漆（约0.5 perms）。但是，有了砌体或灰泥覆层，最好让它蒸发更多。
由于外部烟囱没有屋顶悬垂，因此最重要的大量水处理细节非常重要，因为在隔离冬季较冷的护套层中，任何将散装水引入绝缘烟囱的过失的故障都有很大的损害。。后通气的覆层（例如乙烯基或砖的气隙等）为弹性因子增加了很多。当前总堆栈是什么样的，顶部有哪种闪烁的细节？
Dana,
Thanks for the reply. You are spot on about chimney chases and the potential for bulk water issues. Mine was recently stripped down and rebuilt due to rot. It consists of 2x4 construction, plywood sheathing, fan-fold insulation, followed by non-insulated vinyl siding. The chimney top was the main culprit with an insufficient skirt. The new chase will be stainless steel with diagonal creases, a 3" skirt, a drip edge, and soldered/welded corners.
When the chase was rebuild, I asked my contractor to install Rockwool Comfort Batt up to the fire stop. He instead installed Rockwool's Safe and Sound product, which I understand to have no R value assigned by the manufacturer and isn't sold as thermal insulation. I've heard speculation that it approximates R11, but have no way of knowing. I do have the opportunity to replace it with Comfort Batt if that's truly helpful. Of course, neither of these products have a kraft facer. When I'm adding drywall to the inside walls, presume from your prior message that I should simply add a coat of interior latex primer and omit the polyethylene vapor barrier and kraft paper?
Many Thanks,
Paul
据报道，Safe'n'sound是R11.7，根据Rockwool Int'l的技术支持，但只有3英寸厚它甚至都不是完整的空腔填充，这使对流热绕过。
//m.etiketa4.com/question/safensound-r-0-vs-comfortbatt-r-15-for-interior-2x4-walls-only
Code minimum walls for US climate zones 3, 4, & 5 would be 2x6/R20, or 2x4/R13 + R5 continuous insulation. I suspect the fan-fold is only R1-1.5-ish, and with only R11.7 not fully filling the cavities it's not even close to meeting code. Since the chase will be one of the WARMEST parts of the house when the heater is in use, the lower-performance wall will negatively impact the overall thermal performance.
将Safe'n'sound换成R15板块，然后在内部侧面的干墙下安装1/2英寸箔脸面对的Polyiso（用铝制型胶带胶带胶带胶带）可能几乎无法满足代码，但是可以肯定的是Polyiso。箔脸脸是真正的蒸气屏障（<0.1 PERMS），干墙层的蒸气阻滞性变得无关紧要，但仍需要作为刚性泡沫的火灾保护。只要外观上的风扇折叠或至少不箔纸，护套就会干燥到乙烯基壁板下的外部。
Dana,
风扇折射的隔热材料被穿孔。
I picked up some 1/2" polyiso for the side and 1" for the back of the chase. Because of the fireplace width requirements vs my chase width, I can only fit 1/2" polyiso on one of the sides and then cover with 1/2" or 5/8" drywall. Could I use 3/8" drywall to cover polyiso? If so, I can have 1/2" polyiso on both sides. I can't find anything on building code regarding which specific drywall thickness and type is required. If it matters, I'm installing a gas fireplace, not a wood burner.
Many Thanks,
Paul
>"Could I use 3/8" drywall to cover polyiso?"
它不符合仅3/8英寸厚的石膏的“热屏障”的规格。但是仅在泡沫和起居空间之间需要热屏障。
Since the chase isn't living space it only really needs an "ignition barrier", as long as there is still half-inch gypsum between the chase and the conditioned space, with no direct air communication between the chase and conditioned space. With those caveats, 3/8" over the foam on on the sides would qualify as an ignition barrier, so it should be fine.
See IRC 2018 section R316 on p77 (p102 in PDF pagination) :
https://www.ci.independence.mo.us/userdocs/ComDev/2018%20INTL%20RESIDENTIAL%20CODE.pdf
太好了，我会那样做。
For the floor of the chase, do you see any concerns with using two layers of 2" XPS rigid foam with a sheet of 3/4" plywood on top? The manufacturer doesn't impose any restrictions with respect to the fireplace sitting on combustibles. This would get the fireplace to the desired height and provide R20 for the floor of the cantilever. Do I need a vapor barrier?
The fireplace weighs about 400 pounds over a 50"x20" space, so I thought I'd use 25 psi foam. Assuming the weight is distributed roughly evenly over that space, it would be much, much less than 25 psi. Any reason to believe the foam wouldn't hold up to compression forces over the long term? It's pretty much impossible to get at once the drywall and finishes go up.
再次感谢，
Paul
Any thoughts on insulating the floor of my chase from above? It's already insulated from below with XPS foam. In fact, it's similar to the diagram linked below except it's XPS instead of polyiso and doesn't have foam blocking to seal off the bay at the foundation wall. Sealing it at the foundation wall confuses me about where the thermal barrier lies.
https://terrylove.com/forums/index.php?threads/insulation-where-floor-joist-joists-overhang-foundation.49767/page-2
如果它在露天空气中悬而未决，则至少需要R19才能达到圣路易斯4A区的IRC 2018最低限度。
房屋的热和压力边界将包括基础墙。除非托梁之间有R19，否则应用连续的R10（或同等）隔离基础，以满足当前的IRC代码，但许多房屋的含量为零。它在那里完成地下室，爬网空间吗？
在追逐基础下的托梁海湾中，空气是否可以自由流到条件空间地板下方（无论地板是否是绝缘的？
The house has a conditioned basement and the fireplace chase cantilevers out over open air. The cantilever (underneath of the chase) was air sealed/insulated from inside the basement by installing 2" XPS foam on top of the plywood floor of the cantilever and on the sides and then foamed in at the seams. The cantilever doesn't have blocking at the foundation wall, so inside air can circulate through the cantilever bays.