Can someone point me toward a resources for calculating whether this stone, in and of itself, would be a sufficient hearth pad?
TIA
TIA
R value 3/4" slate
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webbie
Seasoned Moderator
In general, any such stone would have very little R value.
1 inch of slate is shown about about R=.1 - or 1/10 of one....effectively nothing at all.
It would be fine for a stove or hearth extension which was only there to retard sparks - some stoves call for only this (like ceramic tile 1/4").....but these are usually stoves that are very high on Pedestals. etc.
You would need something below it, like Micore, a couple layers of Durock, etc.
https://www.hearth.com/econtent/index.php/wiki/Hearth_Design/
1 inch of slate is shown about about R=.1 - or 1/10 of one....effectively nothing at all.
It would be fine for a stove or hearth extension which was only there to retard sparks - some stoves call for only this (like ceramic tile 1/4").....but these are usually stoves that are very high on Pedestals. etc.
You would need something below it, like Micore, a couple layers of Durock, etc.
https://www.hearth.com/econtent/index.php/wiki/Hearth_Design/
Thanks.Webmaster said:
I think I am close to being in that situation but not quite. There is an existing fireplace hearth that extends 11" in front of the stove door (not the required 16"). The hearth is also 5 1/2" above the wood floor. So I'm looking at inserting something into the floor in front of the hearth to extend out beyond the code requirements. The 3/4" slate would be flush with the rest of the floor if layed on the sub, over a little sand, and grouted in place, so it would be a simple and gracefull solution... but it would then not be up to code as best as I can figure.
What stove or insert are you installing and what does the manual say about floor protection or R value? you wont get it with just the slate unless all it says in noncombustable surface. And in some cases its now 18"
It's a currently installed Hearthstone Mansfield and I'm just trying to correct my little code problem.
Well per the Hearthstone website
HEARTH REQUIREMENTS AND FLOOR
PROTECTION
If the floor is wood or other combustible flooring, the
stove must be placed on non-combustible floor protection
that extends 16 inches to the front and 8 inches to either
side of the front door opening.
The unit must be placed on a non-combustible floor
protector that extends 16” in front and 6” to each side of
the unit. If installed in an alcove at reduced clearances
with NFPA 211 wall protection, the area in front of the
unit must have an additional insulative R-value of .8, or a
listed floor protection must be used.
/unless you are in an alcove you just need non combustable floor. Id still cut up the subfloor and replace with Duroc
HEARTH REQUIREMENTS AND FLOOR
PROTECTION
If the floor is wood or other combustible flooring, the
stove must be placed on non-combustible floor protection
that extends 16 inches to the front and 8 inches to either
side of the front door opening.
The unit must be placed on a non-combustible floor
protector that extends 16” in front and 6” to each side of
the unit. If installed in an alcove at reduced clearances
with NFPA 211 wall protection, the area in front of the
unit must have an additional insulative R-value of .8, or a
listed floor protection must be used.
/unless you are in an alcove you just need non combustable floor. Id still cut up the subfloor and replace with Duroc
You can get a better idea by looking at these pics:nshif said:
https://www.hearth.com/econtent/index.php/forums/viewthread/3307/#33994
I'm guessing the Duroc subfloor is the way to go.
Its not that much cost or that much extra work and youll be able to sleep better at night knowing everything is above whats necessary.
Thanks for your help.nshif said:
I have one last Q.
Does vertical heigth above a combustable have any bearing an the clearance for code purposes?
webbie
Seasoned Moderator
If the question pertains to a "dropped" hearth, physics would say that the floor protection requirement drops as you add more air space to the vertical. The manual on the other HearthStone (hearth stove?) addresses this specifically with different requirements depending on how far the hearth drops.
In my opinion, you certainly would not have to have the full R value at a point 12" or more in front of the stove, but this is from a common sense only viewpoint. In that area you are really protecting against two things:
1. Sparks, etc. - which we know does not take a R-Value, but rather a non-combustible
2. Heat radiated through the glass, which can be substantial, but is on a 45 degree angle and should not (IMHO) present much of a danger.
Code tends to only address these things in a roundabout way, such as the leg length in NFPA 211. Manufacturers usually don't address it because it would mean testing the stoves in all sorts of various configurations.
An "experiment" would be to fire that sucker up big time for 12+ hours or longer and have a piece of slate or wonderboard laying in front of the hearth and see what kid of temp it hits. My money says you will be able to touch it at all times, which means below 130 degrees.
In my opinion, you certainly would not have to have the full R value at a point 12" or more in front of the stove, but this is from a common sense only viewpoint. In that area you are really protecting against two things:
1. Sparks, etc. - which we know does not take a R-Value, but rather a non-combustible
2. Heat radiated through the glass, which can be substantial, but is on a 45 degree angle and should not (IMHO) present much of a danger.
Code tends to only address these things in a roundabout way, such as the leg length in NFPA 211. Manufacturers usually don't address it because it would mean testing the stoves in all sorts of various configurations.
An "experiment" would be to fire that sucker up big time for 12+ hours or longer and have a piece of slate or wonderboard laying in front of the hearth and see what kid of temp it hits. My money says you will be able to touch it at all times, which means below 130 degrees.
Well I'm just a little embarrased that I ran the test last winter with the hardwood floor unprotected.
The distance from stove door to the edge of the hearth is 11".
The distance from the wood floor up to the lip of the hearth is 5 1/2".
Durring the hottest fires (over 600F) the wood floor in front of the hearth would become warm to the touch, but never too warm to keep your hand in place there. There were a few loading sparks that made there marks on the wood there as well.
So I purhased a piece of honed slate (38" -11" -3/4") to lay in front. And I removed the hardwood those dimensions with chisels.
So I'm thinking it is safe but I want it to also meet code.
The distance from stove door to the edge of the hearth is 11".
The distance from the wood floor up to the lip of the hearth is 5 1/2".
Durring the hottest fires (over 600F) the wood floor in front of the hearth would become warm to the touch, but never too warm to keep your hand in place there. There were a few loading sparks that made there marks on the wood there as well.
So I purhased a piece of honed slate (38" -11" -3/4") to lay in front. And I removed the hardwood those dimensions with chisels.
So I'm thinking it is safe but I want it to also meet code.
Gooserider
Mod Emeritus
If the code quote earlier is accurate, then all you need is non-combustible material. The slate meets that just fine. A layer of Durock wouldn't hurt, but it's not really needed. The big question is the distance from the loading door - the latest NFPA codes say 18" is needed, but the stove manuals (which are only updated @ 5 year intervals) still say 16" in the US. Apparently there is debate in the inspector world as to which is the actual requirement. Elk says 18", Tom Oyen says his local inspectors are still happy w/ 16" - If all you are after is code compliance, I'd say check w/ your local inspector for an opinion, but you'd be safest and cover yourself either way if you went to 18" or better. (IMHO exceeeding specs never hurts...)
Gooserider
Gooserider
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