RE: Hearth . . . no R value needed? Can this be right?

[firefighterjake]

As mentioned in another post I recently purchased a Jotul Oslo and now I'm beginning to work on the hearth protection. However, after reading up on all the R values and K values, the value of Micore and Fiberfrax, layering of Durarock, etc. I realized when I read through the Oslo manual that it only says the floor protection must be of a non-combustible material for protection from radiant heat, sparks and embers and it lists out the sizes and minimum distances (front and back and sides) . . . and yet it never mentions a specific R value requirement until you get to the alcove installation which then specifies both the bottom heatshield and any constructed hearth must have a 1.6 R value.

I realized that the Oslo comes with a rear heatshield installed, but wanted to do the right thing and so I called my dealer who in turn called Jotul who supposedly said that the only requirement for floor protection in a non-alcove installation is the size and that it be non-combustible for ember protection and that 24-gauge sheet metal could even be used to meet this requirement.

Does this seem right? It just kind of blows my mind. I'm thinking at the very least I would want to use 1/2 inch of Durarock and tile . . . which would allow me to build a flush hearth (which my wife would like) although honestly I was originally going to go with a layer of 1/2 inch Durarock, Micore sheet, second Durarock layer and then tile (which is what I figured would provide a good R value.)

I guess what I want to know is if anyone has any experience with Oslos and only relying on the floor protection for ember protection. Obviously, building such a hearth with minimal floor protection could possibly limit future stove choices without doing a re-build. I'm still blown away by this . . . it just doesn't quite seem right . . . but then again having a corner install only 9 inches away from a wall just doesn't seem right either . . . guess I'm used to the old woodstoves and their much larger clearance distances.

 

[jay3000]

I have VERY little radiated heat under my giant Jotul with and ash pan. My cat sleeps under it running full tilt.. She hasn't gone WOOF yet. Seems to me that something to catch the occasional ember that falls out would be plenty. It the stove splits in half and emptys a full load on the floor, one of those fancy pads they sell isn't gonna help much anyway.

This is JUST an opinion. I've probably read 30 or so manuals while searching for a new stove. Many seem very vauge about what is and is not acceptable. Here's a front load stove that stores wood undeneath. Wouldn't want a stray coal to find its' way into the bin.. But it sits on an "approved" pad. I just don't understand. Seems like any non combustible surface would be plenty???

https://www.hearth.com/talk/threads/21008/

 

[jay3000]

Here, read this one. It says a combustible floor must be protected by a non combustible material like tile or concrete board. OR certified to local codes..

(broken link removed to http://www.regency-fire.com/TechDocuments/SpecPages/R-F3100.pdf)

 

[fossil]

A stove with firebrick lining in the floor of the firebox and an integral bottom heatshield, that's up on a pedestal or legs with a bunch of airspace beneath, may need nothing more than a non-combustible pad under it, extending out the required distances all around. If your stove manual says it, then it's true. If you were installing some old non-listed stove, then you'd have to fall back on the requirements of NFPA 211, and build a substantial hearth on which to mount the stove. At least, that's the way I understand it. Rick

 

[elmoleaf]

If I recall, the VC Intrepid manual only specifies non-combustible. No r-value given.
The tile underneath my stove (has bottom heat shield) remains cool to touch even when the stove is going full tilt. The floor actually gets warmer to the sides of the stove than it does directly underneath it.

Build the hearth with some sort of known r-value just in case you end up with a different stove down the road.

 

[begreen]

jake, you read correctly. With the bottom heat shield and the ash pan, many Jotuls just require an ember barrier for a hearth. Your plan for some durock and tile would be fine. If you want to add a layer of metal, no problem. I have no idea why the alcove detail is so much higher, but am beginning to suspect that different people write different section of these manuals. There are frequent inconsistencies in hearth requirements, and not just with Jotul.

 

[firefighterjake]

Thanks for the reinforcement . . . this whole thing just kind of blew me away after having read so many folks going to the nines with multiple layers of Durock, Micore, metal, etc. . . . At this point I'm thinking I will go with a little bit better than the minimum requirement (non-combustible floor) and put down a 1/2 inch of Durock covered with tile to give me a flush or near-flush mounted hearth (realizing though that if I buy another stove down the road I may have to re-build the hearth to meet any R-value requirements.)

 

[dsil]

You won't buy another stove.

 

[firefighterjake]

You won't buy another stove.

That's my sincere hope . . . based on the reviews I'm expecting good things with this stove and suspect the experience will be quite a bit different from when I last used a woodstove back in the early 1990s.

 

[begreen]

The disparity for hearth protection is really bugging me. Now I'm at home and have the Oslo manual out and I see it is not the same hearth requirement as the F400 or F600. Alcove install for the Firelight is R .5. It is implying that the Oslo needs a much higher hearth insulation value. But there is no clear statement about what value is required except for alcove installation. The non-alcove install just says spark resistant. There is a reference to a guide in the appendix, but no speced value, just some examples of how to calculate R value and convert from K value.

Argh! After all of this I called Jotul. The last thing I want to do is give incorrect advice. They confirmed that for your stove the primary concern is ember protection and admitted the documentation is confusing. If you want to make your installation totally skookum, put a layer of thin sheet metal down before the durock. But as far as Jotul is concerned, your plan is fine.

 

[firefighterjake]

The disparity for hearth protection is really bugging me. Now I'm at home and have the Oslo manual out and I see it is not the same hearth requirement as the F400 or F600. Alcove install for the Firelight is R .5. It is implying that the Oslo needs a much higher hearth insulation value. But there is no clear statement about what value is required except for alcove installation. The non-alcove install just says spark resistant. There is a reference to a guide in the appendix, but no speced value, just some examples of how to calculate R value and convert from K value.

Argh! After all of this I called Jotul. The last thing I want to do is give incorrect advice. They confirmed that for your stove the primary concern is ember protection and admitted the documentation is confusing. If you want to make your installation totally skookum, put a layer of thin sheet metal down before the durock. But as far as Jotul is concerned, your plan is fine.

Wow . . . you really take your job as Moderator seriously.

Actually, thank you for going the extra mile and confirming this for me . . . it is sincerely appreciated.

Final question . . . and it's probably a stupid one . . . I'm guessing that the weight of the Oslo, tile and Durock should be fine for a floor consisting of 2 x 10s (16 inches on center) with 1/2-3/4 inch plywood and 3/4 inch particle board . . . just looking for confirmation.

 

[fossil]

...Final question . . . and it's probably a stupid one . . .

No such thing, Jake.

...I'm guessing that the weight of the Oslo, tile and Durock should be fine for a floor consisting of 2 x 10s (16 inches on center) with 1/2-3/4 inch plywood and 3/4 inch particle board . . . just looking for confirmation.

Shouldn't be a problem. The tile/Durock/subfloor sandwich will distribute the load perfectly safely. Rick