Hearth Extension Question

[clearblue16]

so here is the situation....i want to install a wood insert in my existing fireplace....i have heard you need 16" of hearth extension in front of the insert if the hearth extension is at least 1.5" thick....if it is not at least 1.5" thick (raised above floor beyond hearth extension) you need 19.5".....with an insert installed i will have about 18 to 18.5" from the front of the insert to the hardwood floor beyond the concrete hearth which happens to be flush with the hardwood floor beyond....are all those clearances "recommended" or are they binding code? i don't want to be out insurance money if i burn down my house or have a "non code" insert when i go to sell the place....i have seen pre fab hearth extensions that are 48" by 18" and would raise the area enough to meet the 16" requirement....my hearth area is 60 by 19 though so that might look weird.....what about a hearth rug? anyone know a simple way to make a good looking extension? any other advice? thanks

 

[edthedawg]

Tough question. Do you know the underlying structure of the hardwood floor? It's not impossible to modify, but you need to know what you have.

Clearances are code minimums usually - tho i can't say i've ever heard your noted 19.5" for flush - it's usually 18" from the door and the thickness of the hearth is determined by the R- or K-value requirements and what materials the hearth is made of to comply w/ those requirements.

Without seeing it, I would venture to guess your best bet is to extend the flush hearth. But that's a Forever Change and you need to be ready for that...

 

[begreen]

What's the insert? Being under an inch is not the end of the world. If you had 16" in front of the glass last year that would have been code legal.

 

[stejus]

From the sounds of it, you are ok with your distince from the stove door. But...

Inspectors will look at clearances and nothing else. Most will not pass the inspection if you are not following stove's minimum's clearance and good luck with insurance. My insurance company didn't charge me any extra, but they wanted a copy of the inspection. Your hearth is not raised so I'm willing to bet your manual calls for thermal floor protection 18" from the stove door. You need to determine what the hearth is made of and figure out the R and K values. Once you have the values, compare against the manual requirements.

Good luck.

 

[clearblue16]

it is going to be a Hampton HI200.....i will have 18" from the glass to the hearth edge but i keep reading about this footnote that says if the hearth is not raised at least 1.5" then you must have 19.5" of hearth extension and my hearth is flush with the floor!....another question, they say the distance is from the "body face"....is that the glass or the bottom of the unit or the opening plane to the firebox? thanks

 

[stejus]

it is going to be a Hampton HI200.....i will have 18" from the glass to the hearth edge but i keep reading about this footnote that says if the hearth is not raised at least 1.5" then you must have 19.5" of hearth extension and my hearth is flush with the floor!....another question, they say the distance is from the "body face"....is that the glass or the bottom of the unit or the opening plane to the firebox? thanks

I have the HI300 and if it reads the same, it is measured from the glass door. In my case, my hearth is raised, but I didn't meet the 18" out from the glass door. I measured 8" from the glass doors to the edge of the brick hearth. Because my hearth is raised, all I needed to provide was "standard ember floor protection". I installed a hearth rug on top of the wood floor. Then I laid a piece of brownstone (12"x48"x2") on top of the hearth rug (to prevent stone from scratching floor) and it buts up against brick hearth.

So, the way I understand Hampton's spec is like this. Because your hearth is not raised, you have to provide "Thermal Floor Protection" below your stove and 18" out from glass doors. You may already have this with what you have for a fireplace floor and extension.

If you can determine what your fireplace floor and extension are made of (thickness of each layer) we can possibly help with determining R and K values.

 

[oconnor]

From page 8 of the Hampton HI200 manual, your floor covering needs an R value of 1.1 or greater. I had a similar but larger problem with my Kennebec, which needed an R value of 2.92 - crazy high. It is really tough to get a hearth extension flush to the floor with those R values, so if you are intent on making sure you observe them, it will take some work.

In the end, we had no combustibles inside 16", so the R value was not truly an issue, but out to 18 inches, there was no way to do it with a flush hearth, as the floor structures started. So far, I am living with the issue. We poured a cement extension out to 20", but in the end, 3 inches of cement doesn't meet the assigned R value of 2.92. That said, I can't see my floor boards underneath suffering any damage based on the floor temps I've seen yet.

 

[clearblue16]

as far as i can tell it is concrete with a black point on it....i don't know how deep the concrete goes but with the insert installed i will have 18" to the combustible material, but again the problem is it says if the hearth is flush then i need 19.5"

 

[oconnor]

Actually, the problem I see is twofold - you need about 15 inches of concrete to meet the R value spec I think, regardless of 18 inches or 19.5 inches, and you need the 19.5 inches.

Personally I would not worry too much about the R value question when you are dealing with a thick concrete hearth, but I would have a local installer you trust look at it to make sure it is reasonable. The manuall actually gives you two options for the floor covering, the R value spec, or NFPA 211. I'm not fully up on the NFPA 211 code for firplace hearths (i.e. fireplace floors) but something makes me think that your concrete is likely to meet the NFPA211 even if it doesn't meet the R value spec.

As for getting the full 19.5 inches, you could see if the extension was 2 layers, and break the top layer off, cut back the floor, and repour. You might also just raise the insert in the firebox up 2 inches - the effect of raising the firebox would likley give you the effect of increasing the distance to the edge of the current hearth extension - it may be non-standrad, but I have seen it mentioned in other manuals, and it would have the effect of reduring the heat transfered to the floor in front, which is what the specs are all about. Again, maybe a local installer you trust would have some input.

Good luck.