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[begreen]

The testing lab (Omni, Intertek in this case) tests and determines the stove clearances to combustibles and hearth insulation requirement. Unlisted stove requirements are set by fire code (NFPA and based on leg height) not UL. In the case of the 13NC my guess is that the high hearth insulation requirement is due to the proximity of the stove glass to the hearth. It's a pretty low stove.

Usually the hottest part of the hearth starts a few inches past the ash lip. An extreme example of this is the Hearthstone Homestead. With regular 6" legs that stove's hearth requirement is R=2.5, with the shorter 4" leg option this jumps to a whopping R=6.6. Needless to say that is a very restrictive requirement that I suspect directly affects stove sales and was not done arbitrarily.

 

[bholler]

Oh, I'm listening alright. But you haven't convinced me your words are the truth. That takes cold hard evidence. Which you have provided exactly NONE.

That is because I am not permitted to tell you that. I know what the ul standards say because we paid to have access to them. If you want to know you are going to have to pay up. Otherwise you will just have to trust those of us who know more about it than you.

Oh, I'm listening alright. But you haven't convinced me your words are the truth. That takes cold hard evidence. Which you have provided exactly NONE.

You can get a very general overview of the standard online for free though

 

[WoodyIsGoody]

It would be interesting to know how they come up with the numbers though strictly from a knowledge standpoint and not a trying to get around the system standpoint.

Totally agree!

And that might be why the testing is not made readily available!

And that's assuming that testing was actually done. I've seen no evidence presented that there isn't a default level of insulation that is acceptable for all wood burning stoves of a certain height off the hearth that manufacturers can specify without testing it. This seems very likely to me and yet we have self-proclaimed experts that say "no", but they provide no evidence to support their contention. They just expect us to take their word for it even though they have never been in charge of getting a wood burning appliance UL listed.

It makes no sense that they would be so adamant about this particular point without any hard evidence to back it up.

 

[begreen]

Visit some stove shows and talk with the manufacturers. I did that with Englander a couple years ago in SLC. Hearth requirements was one of the topics we discussed. They knew the 13NC requirement was stiff and made sure the Madison addressed that.

This article is specific to wall clearances, but it explains a bit about the testing to UL standards process.
https://www.hearth.com/talk/threads/wood-stove-wall-clearances-primer.147785

PS: I erred. UL sets the standard, they don't test the stove. That is done by Intertek or Omni labs in the US. Past discussion though does indicate a UL lab eng going to the mfg. testing facility in some cases to verify internal testing. @webbie might be able to provide some more insight if he's around.

 

[bholler]

Visit some stove shows and talk with the manufacturers. I did that with Englander a couple years ago in SLC. Hearth requirements was one of the topics we discussed. They knew the 13NC requirement was stiff and made sure the Madison addressed that.

This article is specific to wall clearances, but it explains a bit about the testing to UL standards process.
https://www.hearth.com/talk/threads/wood-stove-wall-clearances-primer.147785

Or go visit factories we have done both it is very interesting and informative.

 

[begreen]

Yes, the testing done at Travis was impressive. They were firing the snot out of an FPX unit when I was there at temps way above what folks would try at home.

 

[bholler]

Yes, the testing done at Travis was impressive. They were firing the snot out of an FPX unit when I was there.

Yeah they really put them through their paces.

 

[RobbieB]

Yes, from what I've read all the testing is with the appliance getting fed all the fuel and air possible. Constantly stoked to peak output and held there until temps stabilize on the thermocouples.

 

[bholler]

Yes, from what I've read all the testing is with the appliance getting fed all the fuel and air possible. Constantly stoked to peak output and held there until temps stabilize on the thermocouples.

That is one test yes. They test for worst case scenarios. So all the people that say it isn't to hot are doing so under normal operating temps. But we all know things can go wrong and the stove can get hotter than we want. That is when it really matters.

 

[Doc C]

So I was thinking about filling in between the frame for the hearth with sand to create a giant heat sink?

Like frame my hearth, fill with sand, then use my r value providing material and then finish it.

Any thoughts on if this would be a good idea or bad idea?

 

[begreen]

I wouldn't bother. With proper insulation on top, there won't be a lot of heat reaching the sand.

 

[bholler]

So I was thinking about filling in between the frame for the hearth with sand to create a giant heat sink?

Like frame my hearth, fill with sand, then use my r value providing material and then finish it.

Any thoughts on if this would be a good idea or bad idea?

And could your floors support that weight anyway?

 

[WoodyIsGoody]

The testing lab (UL in this case) tests and determines the stove clearances to combustibles and hearth insulation requirement.

Well it's not very endearing when you misidentify which lab does the testing.

The manufacturer pays an independent lab to certify to UL standards. And it's the manufacturer, or the independent lab acting as a proxy for the manufacturer who determines what the clearances are that get tested. Then it's pass/fail. If the manufacturer choses a lenient enough distance (or presumably, insulation level in the case of a hearth pad) then it will be certified at those levels/distances. Presumably, if they passed too easily, they could pay a large sum of money to test at closer distances/lower levels of insulation. And, if they fail the test, they must also pay to do the test over (with more clearance or insulation) if they want certification.

Doc C: You will find the excerpts below somewhat revealing.

Setting Safety Standards
Regulation in the Public and Private Sectors
Ross E. Cheit

Excerpts below:

But the fire tests are the guts of UL 1482. They subject the stove to both intense "flash fire" conditions and more stable, long-term burning conditions. The temperature at designated points on the stove's surface and surrounding walls must stay within specified tolerances during three separate tests. The manufacturer specifies the distance the stove should be from the wall during testing. If the stove passes, the subsequent label indicates the precise certified clearance (or "distance to combustibles").

Even the most basic requirement of the three fire tests—that the temperature not rise more than 117° F on exposed surfaces and 90° F on unexposed ones[30] —is largely guesswork. "There is some evidence to support these temperatures," observes a widely respected woodstove expert, but "they are still doubtful. Lots of different temperatures are plausible." A challenge to the rationale for these specific temperature tolerances was raised in the canvass process, but UL was unable to provide a specific response.[31]

The practical necessities attendant to laboratory product testing help explain why guesswork often takes the place of science. In writing performance requirements, UL's engineers are sensitive to the cost of the endeavor. UL will not undertake costly scientific experiments where guesswork seems satisfactory. The engineers also try to keep the cost of the test itself within reasonable limits.

Assessing the quality of UL 1482 as a safety standard is difficult because information about actual fires is limited and there may be significant variations in how the standard is applied.[34] How test results are evaluated may also vary by laboratory. UL 1482 leaves many decisions to the discretion of the testing laboratory.[35] Differences in test methods might allow a woodstove to pass the fire test at, say, twenty-eight inches at one lab and thirty-six inches at another. But since the UL standard itself is based on a combination of educated guesses, an agreed-upon margin of safety, and limited test data, it is likely that stoves certified for thirty-six inches would actually be safe at closer distances.

In other product areas, test data have frequently revealed that UL standards contain large, some say too large, margins of safety. Moreover, manufacturers often build in a margin of safety (actually, a margin of error) when they have their stoves tested. On the basis of stove design alone, engineers cannot calculate the distance at which the stove will pass the UL tests. Therefore, the manufacturer, who specifies the distance at which the stove is to be tested, must estimate the clearance, knowing that an overly optimistic estimate will result in expensive retesting. Accordingly, a stove certified for thirty-six inches might pass the test at a closer distance.

This last quote shows how cost savings can affect the stated clearances. And we are not talking about saving the consumer money. Doc's recent project is the perfect example of this. I know some of you would like to believe product testing is very exacting and meaningful but the end result is very imperfect even if that's all we have to go by. That's why I wasn't willing to make assumptions.

Usually the hottest part of the hearth starts a few inches past the ash lip. An extreme example of this is the Hearthstone Homestead. With regular 6" legs that stove's hearth requirement is R=2.5, with the shorter 4" leg option this jumps to a whopping R=6.6. Needless to say that is a very restrictive requirement that I suspect directly affects stove sales and was not done arbitrarily.

After reading "Setting Safety Standards" it's pretty obvious that it wasn't done completely arbitrarily but, depending upon the educated guesses made before testing began, it maybe not much better than arbitrary. At the very least, a large margin of safety was thrown in to reduce the chances that expensive re-testing would be necessary. In the end we have no idea whether the stove passed by a large margin or a gnat's eyelash! The published clearances are the only safe clearances we have and, since the testing is private, we don't know how much margin of safety each clearance has, just that the certified clearance passed the test.

But feel free to believe the certified clearances have a lot of meaning besides that you need them to maintain insurance coverage and help with getting through code enforcement.

 

[Doc C]

And could your floors support that weight anyway?

I think it would be fine. I have 2x6 on diagnal subfloor with osb or particle board on top. Can't tell yet what they used in this area. With 2x12 24" centers where the stove is I think. Been awhile since I've been under that part of the house

 

[begreen]

Well it's not very endearing when you misidentify which lab does the testing.

Already noted and corrected. You're 8 posts behind.

 

[WoodyIsGoody]

So I was thinking about filling in between the frame for the hearth with sand to create a giant heat sink?

Like frame my hearth, fill with sand, then use my r value providing material and then finish it.

Any thoughts on if this would be a good idea or bad idea?

Once you meet manufacturer's minimum insulation levels you will be safer than a round of bog willow at a wood-burners convention! So what would be the advantage?

 

[Doc C]

Once you meet manufacturer's minimum insulation levels you will be safer than a round of bog willow at a wood-burners convention! So what would be the advantage?

I was thinking to add thermal mass.

 

[WoodyIsGoody]

I was thinking to add thermal mass.

Thermal mass needs to go on the other side of the "insulation". Even then, you stated the hearth stayed cool to the touch. So there's not a lot of heat down there to begin with.

 

[Doc C]

Thermal mass needs to go on the other side of the "insulation". Even then, you stated the hearth stayed cool to the touch. So there's not a lot of heat down there to begin with.

That makes sense.

 

[bholler]

Well it's not very endearing when you misidentify which lab does the testing.

The manufacturer pays an independent lab to certify to UL standards. And it's the manufacturer, or the independent lab acting as a proxy for the manufacturer who determines what the clearances are that get tested. Then it's pass/fail. If the manufacturer choses a lenient enough distance (or presumably, insulation level in the case of a hearth pad) then it will be certified at those levels/distances. Presumably, if they passed too easily, they could pay a large sum of money to test at closer distances/lower levels of insulation. And, if they fail the test, they must also pay to do the test over (with more clearance or insulation) if they want certification.

Doc C: You will find the excerpts below somewhat revealing.

Setting Safety Standards
Regulation in the Public and Private Sectors
Ross E. Cheit

Excerpts below:










This last quote shows how cost savings can affect the stated clearances. And we are not talking about saving the consumer money. Doc's recent project is the perfect example of this. I know some of you would like to believe product testing is very exacting and meaningful but the end result is very imperfect even if that's all we have to go by. That's why I wasn't willing to make assumptions.



After reading "Setting Safety Standards" it's pretty obvious that it wasn't done completely arbitrarily but, depending upon the educated guesses made before testing began, it maybe not much better than arbitrary. At the very least, a large margin of safety was thrown in to reduce the chances that expensive re-testing would be necessary. In the end we have no idea whether the stove passed by a large margin or a gnat's eyelash! The published clearances are the only safe clearances we have and, since the testing is private, we don't know how much margin of safety each clearance has, just that the certified clearance passed the test.

But feel free to believe the certified clearances have a lot of meaning besides that you need them to maintain insurance coverage and help with getting through code enforcement.

Very good you can do some research.

You are right they want to set the clearances at something they know they can pass. But guess what they don't do it by guessing. They do it with in-house testing. So they know what the results are before they go for the expensive ul testing. So no there would be no financial benefit for them to needlessly increase their clearances.

 

[RobbieB]

For R2 you only need 10 inches of masonry. 2 stacks of bricks thick side mortared heavy. Easy.

 

[bholler]

For R2 you only need 10 inches of masonry. 2 stacks of bricks thick side mortared heavy. Easy.

2 bricks don't make 10" they make 8". Besides that is allot of work and allot of weight w hen you can just use a few layers of cement board.

 

[Doc C]

2 bricks don't make 10" they make 8". Besides that is allot of work and allot of weight w hen you can just use a few layers of cement board.

I was actually researching right now how I am going to get to r2 without going real high.

 

[begreen]

There are several threads here on hearth building for the 13NC. Micore 300 is typically used as a base to rapidly build up R value. 1" = R2.06.

 

[bholler]

I was actually researching right now how I am going to get to r2 without going real high.

5 layers of durarock next gen will get you almost there most finish materials will do the rest.