Hearth depth per stove manual

[PaulCT]

Hi,
A couple of questions, as I'm installing my new Osburn 2000 insert this week. My hearth is level with the floor of the fireplace, and is 24" wide slate over concrete. Per the manual of the stove, no additional protection is needed if the hearth depth less the stove extention into the room is greater then 16". However, there is a footnote saying that this is only for hearths that are raised a minimum of 4" above the floor. For hearth's level with the floor, protection is needed with an R value > 2.0 for a minimum of 29"! Why does the height of the hearth warrant such a drastic increase in protection? I meet the minimum for a raised hearth by at least 4 inches, but would require an additional 9" of protection based on a level hearth?

I guess I'm wondering, what does the 4" vertical height offer in terms of protection. I don't want to fail inspection over this.

 

[pen]

Sadly, there are many things like this in manuals. The Englander 30 has what seems to be ridiculously high standards for the hearth pad as well, yet since that's what the testing lab came up with, even if there was an error in testing, that's what needs to be done until / unless someone throws down the bucks to have it run through again.

What always kills me is that the coolest place around my 30 is UNDER the stove. Hot hottest place around this stove is to the front, beyond what is required for hearth protection! I'm guessing it's a similar thing with your stove, and as such, as much as it sucks, those guidelines need to be followed.

pen

 

[PaulCT]

Called Osburn tech support, they say it's due to the heat radiated from the glass. None of their other models have this 29" requirement, even the smaller / larger versions of this one. They are having engineering review the test report and will get back to me. In the mean time, I'm thinking of fabricating an extension to meet the R2.0. I spoke to the inspector, and he said even if it were temporary, it's fine with him, as long as it meets the required specs. I was thinking of something light/portable and cheap: 1' x 4' 1/4" plywood + radiant barrier (R3.7) + slate tile. Anyone see issue with this design? Could be made for about $30-40.

 

[PaulCT]

Osburn had engineering review their test results and confirmed the 29" requirement. Inspector OK'd my proposed extension on the phone. Inspection is scheduled for Weds.

 

[begreen]

Called Osburn tech support, they say it's due to the heat radiated from the glass. None of their other models have this 29" requirement, even the smaller / larger versions of this one. They are having engineering review the test report and will get back to me. In the mean time, I'm thinking of fabricating an extension to meet the R2.0. I spoke to the inspector, and he said even if it were temporary, it's fine with him, as long as it meets the required specs. I was thinking of something light/portable and cheap: 1' x 4' 1/4" plywood + radiant barrier (R3.7) + slate tile. Anyone see issue with this design? Could be made for about $30-40.

1/4" ply is too flexible, IMO. I would use at least 1.2", prefer 3/4". Define radiant barrier. On top of it there will need to be a substrate for the slate.

 

[PaulCT]

Honestly, I'm not too worried about the flexing; this is going to a fairly temporary solution. I'm not even going to grout between tiles, and this is not going to receive much, if any, foot traffic. I was going to use a 16" roll of radiant barrier insulation cut to size under the tile, just to reflect the heat away from the floor.

 

[PaulCT]

Passed inspection today. Just waiting for it to dip below 70 deg. which isn't gonna happen this week. Wound up using a piece of 1/2' MDF as the base for the board.

 

[begreen]

If there is no cement board on top of the MDF then grout is required by code. There must be no opportunity for embers to be in contact with the combustible substrate.