Frustrating Hearth Extension Replacement

[BillGriggs]

I'm replacing a tiled hearth extension. I was able to track down the original install instructions for my fireplace (Superior Fireplace #b1038) and it noted that I needed 1/2" millboard or equivalent below a non-combustible surface.

I has planned to put down 1/2" durock, thinset, and my 3/8" porcelain tiles, but called Superior to make sure this was within their parameters.

The man I talked to said to NOT use durock as it doesn't provide adequete insulation to the floor. I asked what product they do suggest for this and he said to find micore board, and that it should be easily available at the Home Depot. It' not. Nor the local Lowe's, or even fireplace stores.

What do I do now?

 

[DAKSY]

Try here:

Ken Huber, West Coast Manager
1143 52nd Street, Seattle, WA 98107
206-789-2413
[email protected]

 

[BillGriggs]

Thanks Daksy.

Are there any other products that are recommended? It all seems to come back to Micore, but that stuff seems really impossible to find. I found this, which seems similar and makes me think other stuff is out there.

It also says it's good to 2300 degrees with applications including combustion chamber front plates. That seems like it'd be good for a stove hearth, but perhaps overkill for a hearth extension in front of a manufactured fireplace?

 

[kennyp2339]

Check this out.. (broken link removed)

 

[kennyp2339]

Check this out.. (broken link removed)

I think the r value needs to be a minimum of 1.030 for your hearth extension.. but I couldn't find it set in stone, I was going off of this manual... http://woodburningdocuments.com/wp-content/uploads/2017/07/HC-Series.pdf

 

[webby3650]

This is an open fireplace correct? Considering it does nothing but suck air into it and up the flue, why would it need anything but ember protection? If that actually is the requirement, it's simply due to a lack of testing.. the new ZC fireplaces don't require anything more than ember protection. Your local hearth stores don't have micore? We have a big stack of it!

 

[BillGriggs]

I think the r value needs to be a minimum of 1.030 for your hearth extension.. but I couldn't find it set in stone, I was going off of this manual... http://woodburningdocuments.com/wp-content/uploads/2017/07/HC-Series.pdf

Are you basing that off the 1/2" millboard? This fireplace is nearly identical to mine (the instructions are pretty much word-for-word). When I called Superior to ask about "equivalent materials" (as my guide lists it) they quoted me .84k and 2.3 R (which don't even seem like equivalent measurements). That seems really intense for a hearth.

My guess is that they simply quoted me what they recommend for their current fireplaces? Either way I'm guessing I'm still stuck with needing to track down micore board?

 

[BillGriggs]

This is an open fireplace correct? Considering it does nothing but suck air into it and up the flue, why would it need anything but ember protection? If that actually is the requirement, it's simply due to a lack of testing.. the new ZC fireplaces don't require anything more than ember protection. Your local hearth stores don't have micore? We have a big stack of it!

Open with the option of glass doors. From what I've understood in all my reading, a hearth needs to not only protect embers, but also protect the combustible subfloor from radiant heat. As I noted to kennyp2339 above, the company quoted my .84k and 2.3 R which feels really intense, and what they (broken link removed to http://superiorfireplaces.us.com/system/document_files/files/000/000/113/original/126595-01_F_SUP_WRT6036_WRT6042_WRT6050_Indoor_Wood_Fireplace_IICO.pdf?1499984972).

We don't really have hearth stores in the NW? I've called several fireplace shops and they don't carry anything like that. I would essentially have to special-order it online.

 

[WoodyIsGoody]

From what I've understood in all my reading, a hearth needs to not only protect embers, but also protect the combustible subfloor from radiant heat.

Exactly. And it's a good idea to follow the manufacturers requirements if you're going to have it inspected and you want to maintain insurance in good standing.

As I noted to kennyp2339 above, the company quoted my .84k and 2.3 R which feels really intense, and what they (broken link removed to http://superiorfireplaces.us.com/system/document_files/files/000/000/113/original/126595-01_F_SUP_WRT6036_WRT6042_WRT6050_Indoor_Wood_Fireplace_IICO.pdf?1499984972).

Those are equivalent if 2" thick. But I don't think the original requirement of 1/2" millboard would meet that spec (R 2.3 ) Maybe you could contact the manufacturer of Micore and ask them what they would recommend as being equivalent thermal protection to 1/2" millboard.

We don't really have hearth stores in the NW? I've called several fireplace shops and they don't carry anything like that. I would essentially have to special-order it online.

I would call US Gypsum to ask about local distributors.

 

[kennyp2339]

Yes, I simply took from the old instructions circa 1985? Says 1/2" mill board, looked up today's r rating of a 1/2" mill board and came up with that number which is kind of high, considering that the actual stove can be placed directly on a "firm" combustible floor.
I don't think dura rock was invented yet back in 1985, also the actual testing of the hearth wasn't as technical yet.
But you always have to go by the manufacturers minimum protection

 

[BillGriggs]

Exactly. And it's a good idea to follow the manufacturers requirements if you're going to have it inspected and you want to maintain insurance in good standing.

Absolutely. I don't want to cut corners and put the house at risk. I'm going to stick to what was originally installed and what was in their original installation instructions.

Those are equivalent if 2" thick. But I don't think the original requirement of 1/2" millboard would meet that spec (R 2.3 ) Maybe you could contact the manufacturer of Micore and ask them what they would recommend as being equivalent thermal protection to 1/2" millboard.

I would call US Gypsum to ask about local distributors.

Strange, right? My guess is that Superior just shot super safe on their new installation instructions, and without proper measurements for their older models are directing people to the new stuff. It seems like the stats I got rival or surpass some woodstove stuff?

I'm going to work on tracking down some Micore today. Really feels like it's available far more on the East Coast which makes me wonder if there's a rival product out here in the NW.

 

[BillGriggs]

Yes, I simply took from the old instructions circa 1985? Says 1/2" mill board, looked up today's r rating of a 1/2" mill board and came up with that number which is kind of high, considering that the actual stove can be placed directly on a "firm" combustible floor.
I don't think dura rock was invented yet back in 1985, also the actual testing of the hearth wasn't as technical yet.
But you always have to go by the manufacturers minimum protection

That's where I've landed too. I think 1/2" of Micore + durock and tile will surpass what I originally had. The odd thing is this isn't even a stove, just a manufactured fireplace. I'm sure radiant heat protection is part of the equation, but it seems like the hearth in this case would mostly be for keeping elements away from the front of the unit and for ember protection.

 

[webby3650]

Absolutely. I don't want to cut corners and put the house at risk. I'm going to stick to what was originally installed and what was in their original installation instructions.




Strange, right? My guess is that Superior just shot super safe on their new installation instructions, and without proper measurements for their older models are directing people to the new stuff. It seems like the stats I got rival or surpass some woodstove stuff?

I'm going to work on tracking down some Micore today. Really feels like it's available far more on the East Coast which makes me wonder if there's a rival product out here in the NW.

That's because they never spent the money on testing it thoroughly. Think about it, there's no where near the radiant heat coming off that flame as there is on a wood stove, most of which only require ember protection. Follow the manufacturers guidlines if you see fit. But, on this one, I'd do durrock and tile and call it good.

 

[kennyp2339]

That's where I've landed too. I think 1/2" of Micore + durock and tile will surpass what I originally had. The odd thing is this isn't even a stove, just a manufactured fireplace. I'm sure radiant heat protection is part of the equation, but it seems like the hearth in this case would mostly be for keeping elements away from the front of the unit and for ember protection.

Just watch the new height of the hearth, you don't want to block any vents / holes in the unit if there low on the fireplace.

 

[BillGriggs]

Just watch the new height of the hearth, you don't want to block any vents / holes in the unit if there low on the fireplace.

Thanks! I think I'll be ok there. The instructions say not to go higher than 2", and I think even with 1/2" micore, tile, and morter, I'll be below that.

 

[webby3650]

You won't be able to bond tile to the micore. You'd still need cement board or ditra to make the bond.

 

[BillGriggs]

You won't be able to bond tile to the micore. You'd still need cement board or ditra to make the bond.

I've seen some people claim this works, but it seems far too soft to me. My plan is to screw a piece of 1/4" or 1/2" durock down to the subfloor through the micore. I wasn't able to find good information on ditra for hearth uses. Even if it's mostly ok, I could see the heat adversely affecting the plastic and ultimately messing with the tile bed.

 

[WoodyIsGoody]

You won't be able to bond tile to the micore. You'd still need cement board or ditra to make the bond.

Ditra cannot replace cement board. The bonding requirements for Ditra are identical to that of tile. The Ditra MUST be well bonded and, as far as I know, the only approved bond is with mortar.

 

[BillGriggs]

Ditra cannot replace cement board. The bonding requirements for Ditra are identical to that of tile. The Ditra MUST be well bonded and, as far as I know, the only approved bond is with mortar.

Yes, I haven't gone hands-on with micore yet, but from what I've seen online it seems way too soft to bind it to anything with thinset. My plan is to get the 1/2" micore, 1/4" durock, and then 1 1/4" durock screws to hold the whole thing down.

The original hearth was made of tiles adhered to millboard with some grout in them and it held up pretty fine. I think the addition of durock will help the new tiles (which are thicker) and provide a tiny bit of extra insulation.

 

[webby3650]

Sounds like a good plan. I'd go with 1-1/2" screws though.
If you were close by, I'd give you a piece of micore.

 

[BillGriggs]

Sounds like a good plan. I'd go with 1-1/2" screws though.
If you were close by, I'd give you a piece of micore.

Thanks! Thanks to USG, I think we've been able to track down a 4'x8' sheet, which will do us nicely.