Kennebec hearth clearance question

[georgia]

Hi,
Just about to buy a Jotul Kennebec insert, but I have one last reservation. It's a masonry fireplace in a 50 yr old house, with brick covering the wall floor to ceiling, about 55 inches wide. The fireplace is 22" deep, so I can insert it as flush as it will go. However, the hearth only extends 13 inches from the brick facing. It is raised 8 inches. I'm looking for opinions on whether this is a problem. The specs I have seen on various inserts call for 16-18 inches for the hearth. I'm hoping that the 8 inch height of the hearth helps with that clearance issue. I would love not to have to work on the fireplace, and the Kennebec is a perfect fit. Dealers say no problem, but I'd love an unbiased opinion.
thanks!

 

[begreen]

I'm surprised the dealer said that. Ask the dealer if they are taking out a permit on the installation and if that is included in the installation price. If you find the dealer is cutting corners, you should be careful they are not being cut elsewhere. Will the insert be installed with a full liner and block-off plate? Is an insulated liner required, (exterior chimney)?

The stove will need the 18" hearth clearance to comply with code. The first time a big spark pops out unexpectedly from the fire, or a log decides to roll out, you will appreciate the reason for the generous hearth. Don't despair, there is a reasonable solution. You don't need to tear anything out. A floor level hearth extension can be built out 10" to meet code. This can be tiled, brick or stone and if done right, it will fit right in.

 

[georgia]

I hadn't thought about logs rolling out, the last wood stove I had 25 years ago was freestanding and loaded lengthwise, so there was no chance of that. I've talked to two dealers and neither has mentioned permits. I guess I need to inquire about that. Thanks for your feedback, this forum is a great source of information.

 

[Mike Wilson]

The dealer is lying to you. It is a problem. The Kennebec throws out significant heat to the floor in front of it... as in, your floor will get hot. Add that to the issue of embers and splits falling/popping out, and your hearth won't cut it. Per the Kennebec manual, you need 18 inches in front of the glass doors. As the stove, fully inserted into the fireplace with the minimum protruding onto the hearth, sticks out 2.5 inches, and you need 18 in front of that, then you technically need a 20.5 inch hearth. That said, I have heard of a few people running them with 20 inch standard hearths with no problems, although it is technically wrong.

Sorry for the bad news...

-- Mike

 

[georgia]

Well shucks, I had hoped the 8" rise would dissipate the heat enough. I guess I will look into extending the hearth on the floor, although I am not sure that will look right. Ripping the hearth out and rebuilding at floor level would be hard (I think) because the brick facing on the wall sits on the hearth bricks. Extending the 8" high hearth out another 10 inches would be a traffic flow issue I am afraid. Guess I will see if I can find some pictures of similar situations.

Your Kennebec looks great. The color looks pretty different than what I have seen in the brochures, which show black, blue black enamel and iron paint - which looks sort of light grey. Is it a special order or something?

 

[Mike Wilson]

Thanks for the compliments. My Kennebec is the iron color that's in the brochure... and yes, it doesn't look the same way in person as it does in their catalog. My wife did not want a black insert, no matter what... and we agreed that this one looked well with the granite surround on the fireplace.

As for your hearth clearances, you will need a minimum of 16 inches for any insert, and more likely 18 inches. I believe the NFPA requires 18 inches in front of inserts now, unless the manual specifies otherwise... and then it would be back to the minimum of 16 inches. Something like that. Either way, to do this, you'll be extending your hearth. Either that, or explore pellet inserts, however in my opinion, the price of pellets makes pellet inserts undesirable, unless you are burning propane to heat your home.

-- Mike

 

[nshif]

Is there a floor R value specified in the manual or just ember protection? If the R value is not to high or its only ember protection ( fire proof surface ) then a layer of duroc with tile on top for the extension will suffice and not impeade traffic flow

 

[Mike Wilson]

Here's what it says in the manual.

"Hearth protection must be noncombustible insulating board, having an R value of 2.92 (0.343 K-value) such as Kaowool 2600 #15 or the equivalent mortared masonry material."

"The protection must extend at least 18 inches forward from the glass panel in the fireplace insert doors."
"Protection must extend 20 inches to both sides of the centerline of the insert."

-- Mike

 

[nshif]

Well if thats what the manual says thats what you gotta do. I wonder if the original hearth is 2.92?

 

[Gooserider]

According to the chart in the Wiki article, common brick is R-0.8 per 4" of thickness... If you had 8" then it is only 1.6, plus whatever is under the floor...

In terms of the extension, the 8" does give some heat dissipation, though it's unclear about just how much. However it is possible to build an extension flush with the floor. Pick your width, which I would base on the dimensions of whatever surface material you will use so as to avoid cutting. Cut out whatever existing floor cover you have, and possibly the first layer of subfloor. If you need really heavy insulation, you might also need to remove the subfloor decking, in which case I would sister a cleat to each side of each joist, and fill back in with 2x blocking between the joists.

Then build back up with Durock, and possibly Micore and then put your tile or stone on top.

If you do a search back a little ways you can see where I put a slate tile extension in flush with the floor in front of my 4" brick hearth - came out looking great.

Gooserider

 

[georgia]

Well that kinda scared me about the R-value of the original brick hearth so I went and measured the chimney down in the crawlspace of the house. (The chimney is central to the house and serves two back-to-back fireplaces.) The brick hearth sits on cinder blocks that go all the way down to dirt so I'm safe there.

Gooserider, I searched around - is yours the sort pf pyramid shaped brick fireplace with multi colored slate in front ? Pretty cool looking. But I think I'd like to put something in that matches the existing hearth - so I guess I need to start searching for some sort of brick veneer/paver that comes close and get it as flush as possible. I guess now's the time to see about reinforcing a joist or two to see if I can take some sag out of that floor. As with all projects, it's one layer after another. And I thought we were going to just pop in this perfect-fit insert. Hah.

So now let me ask this. THe hearth is about 55 inches wide x 14 inches deep x 8 inches high. We'd like to get a stove in sooner than next winter, and its clearly going to take us at least a month or two to get the extension figured out and completed. Would it be safe to extend it twmporarily with a piece of stove board attached to the wood floor, and finish the job when we get the materials and design together? Would this live up to code requirements?

 

[Gooserider]

Well that kinda scared me about the R-value of the original brick hearth so I went and measured the chimney down in the crawlspace of the house. (The chimney is central to the house and serves two back-to-back fireplaces.) The brick hearth sits on cinder blocks that go all the way down to dirt so I'm safe there.

Sounds good, just make sure they don't pass any floor joists through the blocks or attach them to the blocks. Hopefully they don't but it's not unusual to see that.

[/quote]Gooserider, I searched around - is yours the sort pf pyramid shaped brick fireplace with multi colored slate in front ? Pretty cool looking. But I think I'd like to put something in that matches the existing hearth - so I guess I need to start searching for some sort of brick veneer/paver that comes close and get it as flush as possible. I guess now's the time to see about reinforcing a joist or two to see if I can take some sag out of that floor. As with all projects, it's one layer after another. And I thought we were going to just pop in this perfect-fit insert. Hah.[/quote]

Yes, though we call it the "Brick Rocket" :coolsmile: The slate was chosen because we have a front entryway that doesn't show in the photos, but is just to the left of the hearth, using the same style of slate. The left end of the extension actually ties into it. We decided that rather than using some sort of tile, it would be best to match the slate and minimize the number of different materials in the room. It worked out to be an almost perfect match except that I wasn't able to get the grout on the old slate as clean as I would have liked, so it is darker than the new slate :long: I can live with that...

You will need to make sure the floor under the extension is stiff enough, if there is excessive flex the flooring will eventually fail. The John Bridge tile site does have a calculator to let you figure that. If you have access to the joists underneath, the easiest way to stiffen things up is just to sister the joists in question.

[/quote]So now let me ask this. THe hearth is about 55 inches wide x 14 inches deep x 8 inches high. We'd like to get a stove in sooner than next winter, and its clearly going to take us at least a month or two to get the extension figured out and completed. Would it be safe to extend it twmporarily with a piece of stove board attached to the wood floor, and finish the job when we get the materials and design together? Would this live up to code requirements?[/quote]

Not sure what you mean by "stove board" but I would think that a layer or two of Durock would do it, or possibly (albeit more expensive) a pre-fab hearth extension... More importantly you might want to talk to your local inspections people to see if they will buy off on something like that. Sometimes there is code, and then there is how the code people interpret it, so it helps to ask first and avoid headaches later.

Gooserider