Hearth fabrication, R value vs combustion proof

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SteveA

New Member
Aug 29, 2014
19
upstate ny
I'm prepping to put in a pellet insert and the manufacturer specs R of at least 3 for the hearth, which is pretty darn high. Right now there is some bluestone over some type of unknown sheet material, this certainly will not meet it, so i am going to gut it and fab my own. My question is does the hearth through and through have to be made of non combustible material? If so, this will be difficult, in fact I'm not even sure how to do it other then making it very thick (6" on wonder board) or searching out some hard to get material (microcore 160). I would prefer instead to meet the R value with traditional lumber with insulation and tile/stone top over say 1/2" of wonderboard, I would probably end up with a finished height of <3", but this would use combustible material, is that OK?

Oh and I see a lot of posts with folks using steel studs, noncombustible yes, but LOW R value!
 
No it has to be non combustible until you reach that r value. After you get to the required r value you can use combustibles but not before
 
I'm prepping to put in a pellet insert

What model/brand do you try to install? Is that insert maybe supposed to go into a masonry fireplace? Why did you not chose a pellet stove?
 
What model/brand do you try to install? Is that insert maybe supposed to go into a masonry fireplace? Why did you not chose a pellet stove?

It's a quadrafire classic bay. The install instructions covers non masonry applications. This home I bought had a prefab fireplace that was falling apart, I figured an insert would be an easy fit (maybe not!).
 
Call the people at Roxul and see what the R value of 1" is. 3.5 inch is R15 and good for 2100 degrees according to their website. If you put that between 2 sheets of wonder board it might get you there.
 
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Wow, I haven't seen that Roxul Comfort Board before, looks like a great option for building a hearth pad. A quick google search also indicates it tricky to find in the US: all the retail links were to Canadian sites.

If you compress that 1 inch of Roxul R15 between two sheets of Durock, it's insulation value will be basically nill. You need dead air space (i.e. fully lofted insulation) for it to work.
 
Wow, I haven't seen that Roxul Comfort Board before, looks like a great option for building a hearth pad. A quick google search also indicates it tricky to find in the US: all the retail links were to Canadian sites.
yeah the OP is in upstate NY so The boarder is most likely close.
Just in case ....that is why I threw Mircore in the mix. It's made by USG and can be bought in many more places in the US. Gets the OP close to the R 3 he needs
 
Take a look at Fiberglas duct board under dura rock.
 
A single sheet of glass is R1
 
Well, I have not been able to find any of the high R materials locally, I am not really upstate, being south of albany and all. It does look like the material can be ordered and delivered, the cost is high, but not outrageous.

I have not looked for the duct board yet, I image it is quite compressable?
 
I just took a quick look at the manual where it mentions this as an option: Quadra-Fire floor protector, Part 811-0730

Does that not work in your case or can you not get it?
 
Well, I have not been able to find any of the high R materials locally, I am not really upstate, being south of albany and all. It does look like the material can be ordered and delivered, the cost is high, but not outrageous.

I have not looked for the duct board yet, I image it is quite compressable?
Hudson Valley Area? I'll check around I know a few places that carry some of the materials metioned.
 
Hudson Valley Area? I'll check around I know a few places that carry some of the materials metioned.

Yes Owen, I'm in the hudson valley, if you could let me know where to get some Microcore or Roxul locally that would make my day.

Grisu, I have not talked to the distributor yet, for some reason, i thought the protector did not go into the hearth, I'm not sure where I got that impression, but should follow up on that, it could be the easy out...
 
Steve, I have a call in to a contact at Lowes. He is checking into Micore SB mineral fiber board it has a R value of 1.47 per 1/2" so stacking two will give you a R value of 2.96 at 1". With a layer of tile/stone like you said in the OP then you should be at 4. He is checking on it getting shipped to Middletown Lowes. I lived in Orange cty for a LONG time so I know the area well. If you rather it to another store let me know.

Edit: Once I know it is possible I will PM you his name and info so you can work it out.
 
Ok tracked it down for you. The place is Marjam building Materials in Newburgh. They carry it in stock they only have the Micore 300 which is 2.18 R value per inch and they have both 1/2" and 3/4" I'll PM you the Contact info.
 
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Steve A,

Did you figure this out yet? I am in a similar situation and I'm going to talk to my dealer tomorrow about the quadra fire floor protector (part 811-0730). I have a 1+ inch air gap (which is what the installation manual calls out), but the floor is kind of flimsy and needs to be better supported (the air gap doesn't make sense if I then need to support it with some sort of material that has an R value of less then 3 like the manual calls for). I'm looking to take the floor out and put the floor protector down. Wondering if you've talked to you dealer about it yet.
 
Yes. His reply was "the bottom of the insert is not hot, don't worry about it". On one hand, I think this guy is a short cutter, on the other hand, he has a good reputation and has been selling stoves for 35 years at the same location. My hearth is thin (prebuilt fireplace), but there does seem to be some type of substrate under the thin stone. Does it meet R3? I have no clue, we'll see what the inspector says. Do you have a pix of the floor protector? I'm curious what it looks like.
 
So my stove is in and I've had it running. Right now there is a thin metal floor from the pre fab fireplace still present. There is about a 1.5 inch air gap, but the metal needed to be supported so my installer wanted to put some tiles under there. The floor under the fireplace is ply wood. I dont agree with this method. Plus, with the stove running, I have taken temperature readings of the floor and it gets hotter (probably around 100 degrees, maybe a little more). Is that terrible, probably not, but I dont want the floor getting that hot being that this thing will be running 24/7 and when im not home.

I went this morning to my dealer and ordered the floor protector and will have it in a week and a half probably. When I get it I will post a picture.
 
So I finally got the floor protector in. Its not quite what I expected, but in hindsight it makes more sense than what I had in my head. Should have it in sometime next week and I will post pictures with it installed.
 

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Here is the floor installed. There was a 1" gap from the top of my stone hearth to the floor under the stove. Once I cut the metal floor out of the pre-fab fireplace I put some hardi backer cement board down to make it level with the hearth then put quadra fire floor protector down. Attached pictures show the metal floor of the pre-fab cutout with the hardiback down and the final product with the insert installed.
 

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I used durock to get the level up on my hacked up prebuilt and cemented it down. In a streak of good luck, I found the floor proctector (slightly dented) on the cheap, it is pretty simple, but gets the job done, the floor is cool as a cucumber now. Did you just set the insert on the protector? I drilled holes in it where the pallet bolts were on the stove, so the insert and stove move together.

BTW, I like the look of you setup. I had grand plans to rebuild the fugly hearth area I have, but at this point, I'm just glad to have the stove in.
 
I just put the insert on the floor protector. I figure those bars on the sides stop it from sliding further into the fireplace and if it slides out a bit when I move the insert for cleaning or something its not the end of the world. It didn't really move much anyway once the weight of the insert was on it.

Glad you go it all setup. Thanks for the compliment. I may tear the pre-fab out in the future and try and match the tile but for now its in and I think it came out pretty good.
 
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