Hello!
Like others have said in their first post, I’ve been a lurker here for a while here and have learned a lot from various threads, which I really appreciate. There is also some confusing information out there online and I would like to get your opinions (hopefully blessings?) on what I’m thinking of doing for the hearth I’m building for a new Woodstock Soapstone Co Absolute Steel Hybrid that is being delivered in about a week. So, going from the bottom up, here are my plans, with some questions thrown in. Note that I'm especially confused about insulation for the chase, at the bottom of the post.
UNDERLAYMENT/R-values: The specs for this stove require an R-value of only 0.41 for the hearth beneath it. (It comes with a required bottom heat shield). I want a low profile hearth, flush with the floor if possible. So I’m thinking of using a 1/2” layer of Durock applied over a coat of thinset on the plywood substrate and screwed down (per D-rock instructions). Then more thinset topped by ceramic tiles of various sizes to make a mosaic pattern. I’m also throwing in a few river stones throughout parts of the hearth.
If Next Gen Durock’s R-val is 0.39 and ceramic tile’s is 0.02, that would get me to 0.41. **The one really annoying thing I’ve come across recently—after lots of research that pointed to Durock being the better choice for hearth/r-values—is Durock’s own specs that state NextGen Durock shouldn’t be used for applications where the surface temp will be above 200º (or 225º for the 0.625 thickness). I’m hoping they are just saying that to cover their asses, because so many people have had good success with it in woodstove installations. Any thoughts?
THINSET: From my research, it seems a polymer-modified thinset is best, and I’m thinking of going with Mapei's Keralastic/Kerabond 2-step system for the thinset (mixing the powdered mortar with Keralastic liquid instead of plain water to achieve more flexibility for the temperature fluctuations). Somewhere (not here), I read that for fireplace applications, one should look for a thinset mortar to be rated to 400º F, but I can’t find any thinset that lists that temperature or any actual temperature for designed application/operation. They only mention extreme freeze/thaw cycles for what the polymer-added thinset is best for. Maybe I should go with “refractory cement” or “furnace cement,” but most info on here talks about thinset, which is different (right), and probably better?
GROUT: Sanded grout seems better for this application from what I’ve read, and I’m again thinking of going with Mapei’s KeraColor polymer-added, sanded grout using a 1/8” width between the tiles. Is there any reason I should space the tiles wider than that?
Lastly, INSULATION (which is where I have to start, of course, and really soon!). The piping is going to be going up through my existing exterior-wall chase, where a pre-fab fireplace used to be before I tore it out a couple of weeks ago. Right now I can just see the wood framing and original insulation board (see pic).
For piping, I’m using double-walled stovepipe out of the rear-flue exit on the stove. The stove itself will sit 8.5" out in front of the old FP as per clearance requirements. There’ll be a double-wall T at the 90º turn up the chase, and from there up, stainless steel chimney pipe for 15’ including the outer chimney.
So even though clearances are more than met on all sides, for a finished look I think I’m going to put 1/2” Durock inside the fireplace opening, painted with fire-safe paint, with a few tiles where the inside/outside edges of the fireplace walls meet, going out 5 inches to 1 foot.
I’ve been told I should put insulation behind the Durock, which makes sense for safety and energy savings. Advice varies on how far up the chimney to insulate, from the lower 6 feet only, to at least the upper chase and whatever else you want, since the air will be colder up there. Because this space is somewhat open to airflow, I’m thinking of using the safer, greener Roxul mineral wool insulation either in ComfortBatt form or Comfortboard 80, which both seem to be available here where I live. Is there any better product you would recommend? Of all the products I’ve researched in the whole journey, this one gives a solid, high temperature rating of 2150ºF, yay!
So I guess my questions here are safety related mostly. I don’t want to go totally overboard but do want to be smart. I probably won’t be burning this stove hot for months and months on end. More likely burning it low since my house is not that huge and hey, I live in North Carolina.
Given that, what do others say about how much of the chase to insulate? If I just did the upper and lower but not the middle, would that create hot/cold air pockets that might be problematic?
Also, is it ok health-wise to have the Roxul insulation uncovered/unfaced in the part of the chase that isn’t visible from the room? Should I instead cover it with Durock or some other alternative? Even though it’s safer than fiberglass to breathe, it could still be an irritant if breathed in. I do have several sheets of metal from the old pre-fab fireplace that I could maybe cover the Roxul with. --And I just saw a thread where begreen mentions crisscrossing string over the batts or boards to hold them in safely.
Finally, some people on here have documented using steel beams instead of wood for the framing in their hearth flooring and background surround. I remember one example where the required R-value was really high, at 6. Do others think that wooden framing is okay in this case, or are steel beams are necessary in the chase, even though it will be mostly stainless steel pipe there and several inches more than a 2” clearance all around it? Would covering the wooden 2x4s with some metal sheeting be recommended as an in-between option?
Thanks to everyone if you got this far and for any help you can give on these questions!
Jenny
pics of gutted chase, and chase from outside with original, now-gone, pre-fab chimney.
![[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation](https://www.hearth.com/talk/data/attachments/186/186554-ff1cce583e51f0ce82f1f1ef26d5b128.jpg?hash=mZjoXq-QlJ "[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation")
![[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation](https://www.hearth.com/talk/attachments/screen-shot-2016-10-18-at-5-20-19-pm-webp.186526/ "[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation")
Like others have said in their first post, I’ve been a lurker here for a while here and have learned a lot from various threads, which I really appreciate. There is also some confusing information out there online and I would like to get your opinions (hopefully blessings?) on what I’m thinking of doing for the hearth I’m building for a new Woodstock Soapstone Co Absolute Steel Hybrid that is being delivered in about a week. So, going from the bottom up, here are my plans, with some questions thrown in. Note that I'm especially confused about insulation for the chase, at the bottom of the post.
UNDERLAYMENT/R-values: The specs for this stove require an R-value of only 0.41 for the hearth beneath it. (It comes with a required bottom heat shield). I want a low profile hearth, flush with the floor if possible. So I’m thinking of using a 1/2” layer of Durock applied over a coat of thinset on the plywood substrate and screwed down (per D-rock instructions). Then more thinset topped by ceramic tiles of various sizes to make a mosaic pattern. I’m also throwing in a few river stones throughout parts of the hearth.
If Next Gen Durock’s R-val is 0.39 and ceramic tile’s is 0.02, that would get me to 0.41. **The one really annoying thing I’ve come across recently—after lots of research that pointed to Durock being the better choice for hearth/r-values—is Durock’s own specs that state NextGen Durock shouldn’t be used for applications where the surface temp will be above 200º (or 225º for the 0.625 thickness). I’m hoping they are just saying that to cover their asses, because so many people have had good success with it in woodstove installations. Any thoughts?
THINSET: From my research, it seems a polymer-modified thinset is best, and I’m thinking of going with Mapei's Keralastic/Kerabond 2-step system for the thinset (mixing the powdered mortar with Keralastic liquid instead of plain water to achieve more flexibility for the temperature fluctuations). Somewhere (not here), I read that for fireplace applications, one should look for a thinset mortar to be rated to 400º F, but I can’t find any thinset that lists that temperature or any actual temperature for designed application/operation. They only mention extreme freeze/thaw cycles for what the polymer-added thinset is best for. Maybe I should go with “refractory cement” or “furnace cement,” but most info on here talks about thinset, which is different (right), and probably better?
GROUT: Sanded grout seems better for this application from what I’ve read, and I’m again thinking of going with Mapei’s KeraColor polymer-added, sanded grout using a 1/8” width between the tiles. Is there any reason I should space the tiles wider than that?
Lastly, INSULATION (which is where I have to start, of course, and really soon!). The piping is going to be going up through my existing exterior-wall chase, where a pre-fab fireplace used to be before I tore it out a couple of weeks ago. Right now I can just see the wood framing and original insulation board (see pic).
For piping, I’m using double-walled stovepipe out of the rear-flue exit on the stove. The stove itself will sit 8.5" out in front of the old FP as per clearance requirements. There’ll be a double-wall T at the 90º turn up the chase, and from there up, stainless steel chimney pipe for 15’ including the outer chimney.
So even though clearances are more than met on all sides, for a finished look I think I’m going to put 1/2” Durock inside the fireplace opening, painted with fire-safe paint, with a few tiles where the inside/outside edges of the fireplace walls meet, going out 5 inches to 1 foot.
I’ve been told I should put insulation behind the Durock, which makes sense for safety and energy savings. Advice varies on how far up the chimney to insulate, from the lower 6 feet only, to at least the upper chase and whatever else you want, since the air will be colder up there. Because this space is somewhat open to airflow, I’m thinking of using the safer, greener Roxul mineral wool insulation either in ComfortBatt form or Comfortboard 80, which both seem to be available here where I live. Is there any better product you would recommend? Of all the products I’ve researched in the whole journey, this one gives a solid, high temperature rating of 2150ºF, yay!
So I guess my questions here are safety related mostly. I don’t want to go totally overboard but do want to be smart. I probably won’t be burning this stove hot for months and months on end. More likely burning it low since my house is not that huge and hey, I live in North Carolina.
Given that, what do others say about how much of the chase to insulate? If I just did the upper and lower but not the middle, would that create hot/cold air pockets that might be problematic?
Also, is it ok health-wise to have the Roxul insulation uncovered/unfaced in the part of the chase that isn’t visible from the room? Should I instead cover it with Durock or some other alternative? Even though it’s safer than fiberglass to breathe, it could still be an irritant if breathed in. I do have several sheets of metal from the old pre-fab fireplace that I could maybe cover the Roxul with. --And I just saw a thread where begreen mentions crisscrossing string over the batts or boards to hold them in safely.
Finally, some people on here have documented using steel beams instead of wood for the framing in their hearth flooring and background surround. I remember one example where the required R-value was really high, at 6. Do others think that wooden framing is okay in this case, or are steel beams are necessary in the chase, even though it will be mostly stainless steel pipe there and several inches more than a 2” clearance all around it? Would covering the wooden 2x4s with some metal sheeting be recommended as an in-between option?
Thanks to everyone if you got this far and for any help you can give on these questions!
Jenny
pics of gutted chase, and chase from outside with original, now-gone, pre-fab chimney.
![[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation](https://www.hearth.com/talk/data/attachments/186/186649-660c754ee02d05764ffbdea575060b34.jpg?hash=CjJO1sn9oY "[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation")
![[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation](https://www.hearth.com/talk/data/attachments/186/186650-a9e151a2c0de4e90d600479799920143.jpg?hash=ERoN1Z0yrl "[Hearth.com] Newbie wood stove install...Qs re: hearth underlayment & insulation")
