Is there flexibility in clearances?

[rsiros]

Hello again... I'm still comtemplating whether to get some protection for my mantle and surrounding trim. I'm through with my break in fires for the Hearthstone Homestead, and last night I burned a real fire... nothing too intense and only for about four hours. I am about six inches under the listed mantle clearances but my mantle and trim are not "shelf-like". There is enough of a contour that there doesn't seem to be a large area where heat is trapped. I kept feeling the mantle and trim, and it was hot but I could easily keep my hand on it without discomfort. I'm going to get some thermometers today and I'll post my results tomorrow. Are the clearances flexible and to be used as a guide for people like me, or are they set in stone and not to be varied from? I figure that everyone has different set-ups and situations and exceptions could be made based on surface temps.

 

[DriftWood]

I think the top of stove to mantle is set in stone for a safe operation. Stoves are UL tested that way any variation and you loose the UL safe install and you are not following the installation instructions, So you are also out of code .

You could call hearthstone and see if a heat shield will get you down 6 inches. A heat shield between stove and mantel will some times let you get them closer and still be safe.

 

[mikeathens]

I'm not any type of authority on this subject, so I'm only giving my opinion and my experiences. My hearth is about 6" shy of "minimum", and I don't quite have the "R" value given in the manual, but the hearth stays cool to the touch all of the time, even during big, hot fires, and even directly under the stove. From other posts, I assume the required R value and hearth dimensions are provided for a log rolling out, sparks, embers, stove breaking in half with a raging fire inside, etc. to keep from buring under direct heat (I can't figure out why else the R value and hearth dimensions are given). At any rate, I am comfortable with my setup, and I don't feel that I am at risk any more than anyone meeting the requirements of the hearth. I'm a bit bothered by it, but it's in and I'm not changing it - as an engineer, I feel that my anal personality is enough extra protection.

BUT...

Regarding chimney clearances, that is another story. My original install was done before I got the house, and it was a few inches shy of the minimum pipe clearances. Like you, I noticed that the wall got pretty hot behind it, but I could put my hand on it. I was always uncomfortable with that. I think the chimney clearances truly are a minimum from combustibles because you are talking about true "in use" radiant heat; not just protection for when something goes terribly wrong. I relocated my stove after I moved in and made sure that I had the minimum PLUS about 4 inches. If I were you, I would make sure that you meet minimum chimney clearances from combustibles. It sucks that you would have to make modifications, but I woudl't screw with that particular guideline. I thinnk you're playing with fire otherwise.

 

[DriftWood]

My hearth is about 6" shy of "minimum", and I don't quite have the "R" value given in the manual, but the hearth stays cool to the touch all of the time, even during big, hot fires, and even directly under the stove.

I think you are playing with fire. R value is just that resistance to heat. Correct code is 18" stove front to floor.

I think the stove fount to floor and hearth R value are set in stone for a safe operation. Stoves are UL tested that way any variation and you loose the UL safe install and you are not following the installation instructions, So you are also out of code .

Any stove related problems even ones not related to hearth or fount clearances and you just gave your insurance a out in a fire claim. Wood stove not installed to code, Wood stove not installed to manufactures instructions. Wood stove install dose meet UL standard. Claim denied.

 

[webbie]

Clearances to mantels are often given depending on the distance that the mantel sticks out, so you could call this flexibility. I have seen manuals and even codes where it is written this way. Still, if it is NOT written this way in your manual or label (or approved by your code official), then your installation is not up to snuff. While I understand that your installation passes the "rule of thumb" test, that is not the way codes are written, and only in the rarest circumstances do you want to use those rules!

There can be flexibility in the way you protect a mantel. A shield can be located at various places, made out of various metals, etc - in order to cut off the direct radiation between the stove top and the mantel.

Another issue is that long and hot burns will get that area MUCH hotter than a 4 hour fire...heat will also soak up through the masonry above the fireplace MUCH MORE after a number of hours. In some ways, the ultimate protection is a heat shield mounted to the fireplace lintel, because it protects both the masonry above and the mantel.

 

[rsiros]

Thanks for the replies and advice guys. My Homestead is hearth mounted with the flex liner through the chimney, and it sits on the fireplace hearth with the rear of the stove just under the lintel. The liner and exhaust are rear exit and go directly into the fireplace and up the chimney. Clearances should not be an issue there, right?
I am hesitant to modify my mantle and attach sheilds and other accessories because it would definately ruin the asthetics and value. If it's a safety issue of course I would modify things. BUT, if it's not necessary then I will leave things as they are. I understand that codes are designed for the general safety for the greater good, but I think we all know that codes (across all trades and fields) cannot take every unique situation into account. I'm mainly concerned with understanding why the clearances are a must even if the surface temps are within acceptable levels.

 

[babalu87]

No

There is a term for what chemical/physical change wood goes through when it is heated and cooled for extended periods of time. I forget what it is called but the wood changes and becomes flammable at much lower temperatures as time goes by.
One day the wood is just hot, the next day and the next day its the same thing.
Then one night when you and your family are upstairs asleep it bursts into flames.

 

[rsiros]

Hmmm... a heat shield attached to the lintel may be just the answer. I do understand the whole insurance thing. Point well taken. Thanks everyone.

 

[webbie]

The fireplace I inspected last year which burned the house down worked fine for one hour fires, and fine for even 8 or 10 hour fires. It may have worked fine for even 24 hour fires. But then the power went out for two days and the homeowners tried to use it to stay warm, it burned the house down.

Based on it getting warm after 4 hours, that means nothing at all.

Here is a rough sketch of the kind of thing I am talking about, which would add greatly to your peace of mind.

A shield like this helps in two ways:
1. Cuts off radiation to the mantel - directly
2. Stops heat from soaking into brick on the face of the fireplace, and then into mantel or framing.

 

[rsiros]

That looks great admin! Just the answer. More people should see that because I've read lots about the heat shields and seen plenty of beautiful setups ruined by the ugliness of a big black projectile sticking out from the mantle. I've also read plenty of posts involving some pretty intense modifications of mantles when your solution would have saved lots of work.

 

[mikeathens]

My hearth is about 6" shy of "minimum", and I don't quite have the "R" value given in the manual, but the hearth stays cool to the touch all of the time, even during big, hot fires, and even directly under the stove.

I think you are playing with fire. R value is just that resistance to heat. Correct code is 18" stove front to floor.

I think the stove fount to floor and hearth R value are set in stone for a safe operation. Stoves are UL tested that way any variation and you loose the UL safe install and you are not following the installation instructions, So you are also out of code .

Any stove related problems even ones not related to hearth or fount clearances and you just gave your insurance a out in a fire claim. Wood stove not installed to code, Wood stove not installed to manufactures instructions. Wood stove install dose meet UL standard. Claim denied.

I knew I was going to take heat on this one. I'm not advocating this; but it's what I have. There is a factor of safety built into this requirement, but regardless I know I SHOULD meet it. I know what R value is, I know (I think I know) the intention behind the minimum hearth distances. Fact of the matter is, when the stove's roaring hot, the floor is cold or cool to the touch all around and under the stove.

SO...what is the intention/safety concern with the min R value between stove/combustibles and the minmum non-combustible hearth width requirements? Am I right that it is for stray embers or logs falling out? You'll note that the requirement on non-loading door sides are considerably less than where the loading door is. And Again, the entire hearth is cool to the touch when the stove is at maximum temp. I really don't need to hear what a moron or criminal I am for not having a hearth up to code again, I just want to hear the reason behind the numbers...if I understand the rationale correctly, then I'm comfortable with my setup.

 

[mikeathens]

I was thinking about this whole hearth code thing, and I'd like to hear how many installs of people on this site meet ALL requirements COMPLETELY. Let's start a new thread on this one, if necessary. We all know what is "right" and how our stoves should be installed. How many of us cheated on our hearth R value a little - we got it to 1.15, and said "good enough" because that extra layer was going to make the hearth too high or make it so we'd have to cut a crap-load of extra tile or stone? How many of us built our hearths and mis-calculated a bit, so we are 1.5" shy of the minimum hearth width requirement? How many discovered that the location of our roof rafters made it so we could either place the chimney 15" from the wall, or 31" from the wall, with the latter making it so the stove was just too far out into the room, so we cheated on our clearance just a bit? etc. etc. We all know what we are supposed to do...just how many of us are on here pretending to be code and minimum clearance hard-liners, but have a little secret about our installations that we don't want anyone else to know?

 

[rsiros]

I have to snicker at that Mike... I'm sure everyone has said, "good enough" at some point where safety wasn't compromised, but people don't want to advertise that incase someone misinterprets and does something foolish as a result. I'm always hesitant to give advice that doesn't meet codes but sometimes there are other ways of doing things while keeping safety in mind. That's the beauty of a forum like this.

 

[mikeathens]

I guess that's what I'm trying to figure out...is saftey compromised in my install? Yes, I'm shy on my R value, I'm shy on my hearth width (it's more like 1.5", not 6" short). But is safety compromised? How much? My hearth is cool to the touch. I know a log could fall out, but I am ultra careful wiht the stove and it's operations (otherwise, I wouldn't bother with these forums). Is mine "good enough"? Canada code requires 18"; US is 16 (according to my manual). Is a stove less safe with the US requirements? Why isn't it uniform? So if you have an older hearth say, from 1970, that met code then but not now, is it suddenly unsafe? If code changes tomorrow and requires a 3.5 R value over combustibles, and a 24" load door hearth width, do we all tear out our hearths and rebuild them? I'm going to guess no.

 

[webbie]

Mike, I would say that I or other long time industry folks could walk into over 90% of installations and find something that didn't meet the letter of the code. And if that was not enough, we could point to something else - like the "workmanship".

You are right to ask those questions - just for the sake of learning. Each one would require a very long answer.

For instance, as to hearth measurements being different in front, there are a number of issues:
1. The most obvious, the sparks (if a loading door is present).
2. The glass doors of many stoves radiates heat vastly better than the sides and rear. I have seen GAS stoves and inserts with deep hearth requirements because of the infrared thrown out.

I do understand all those gray areas - which is what we often discuss here. But as far as protection in front of a large loading door, my question would be "why not" use a temporary (take up in summer) piece of granite, stone, slate.....or even a temp $50 stoveboard extension? It provides a good place to drop the wood and keep the tools while fiddling with the stove.

Also, we have to keep in mind that the manuals and codes often conflict. A small stove might call for a small hearth extension in front, and in these cases (IMHO), the testing and manual/label trump the code. In some ways, the code is written for "generic", which hardly even exists anymore.

 

[mikeathens]

Well, thak you for the response. I would like to have the two questions answered: Why the minimum hearth distances, and why the minimum R value for the hearth? My Heritage's front load door is NEVER used (it makes too much of a mess). Is it ONLY for the protection of the floor for logs/sparks, or are there other reasons? radiant heat onto my hearth is less than the sunlight on the side of my log cabin in July.

 

[rsiros]

Mike... as is the case in most trades, codes are the general standard that will apply to most cases-especially those of new construction. This was my original intent in posting... challenging codes that may not apply to our individual cases. If you are confident that your setup is safe, then your only concern would be collecting insurance money if something should happen. I was not completely confident in my case so I sought the help of the forum users.

 

[mikeathens]

I guess that's not the issue; I just want to know if anyone truly knows the intention behind the hearth requirements. If anyone does, and if my assumptions are correct, then I'm happy with my setup and confident that it's safe..

 

[Metal]

If you ask us what is right and what the code requires, we can answer you. If you are asking if your situation is "safe enough" for you, we can not answer that because we don't know much risk you are willing to take.

Some people feel fine burning a double barrel Vogelzang on the living room carpet, others will double the R-values and clearances or not even install a wood-burner for safety's sake.

You know what the codes are and you know what you are going to do (you value pretty over safe, which is fine as long as my family is not involved), so the rest is all just semantics.

 

[mikeathens]

Please note that previously, I asked to not be told what an idiot I am becasue my hearth doesn't meet code. With that said, my question is still not answered.

 

[webbie]

I guess that's not the issue; I just want to know if anyone truly knows the intention behind the hearth requirements. If anyone does, and if my assumptions are correct, then I'm happy with my setup and confident that it's safe..

False logic.

You are asking a general question, when your setup is specific!

Your question was clearly answered. Beside the obvious (sparks), there is additional heat radiation out through the front and glass of many stoves. Is that clear? Think about it - if you designed a stove, which way would you design for it to put the heat out? Would you design it to put heat out the rear? No, you would design it to project heat into the room!

Notice the manual for the Hearthstone enclosed (not yours) shows a different R value depending on how far the stove is ABOVE the hearth. Why? If it was only for sparks, a minimal R value should do for all the installations. But yet they are calling for a MASSIVE R-Value in some cases.....

That is called "testing", and means they tested it and failed until they met the requirements of the UL standard.

I hope that clears up how the standards and specs are made - on individual stoves! NFPA makes some that are more "generic" in case the other info cannot be found.

 

[mikeathens]

Yes, Craig, that clears it up! Your previous post said this, but I wan't sure if these were the ONLY reasons. Yes, I have a specifc setup, but I was asking a general question about WHY the requirements were in place (or more generally, why they were developed, and what conditions were considered). thanks for clearing that up.

 

[tradergordo]

I've been thinking about some of these questions too. I just don't understand why some manuals say a single layer of durock, R value = .26 is "good enough" and other stoves want an r-value of 1.19 (five layers of durock) when neither stove puts much of any heat down on the hearth. It sure seems like the requirement must have something to do with oddball things happening like sparks or flaming logs falling out, or the stove cracking in half - but if that were the case then why shouldn't a small stove have basically the same requirement as a bigger stove?

 

[Metal]

When the stoves are tested the combustibles cannot attain a temperature higher than a set number (like 75º higher than ambient or something like that). In your example Stove A only needed one layer to keep the combustibles at the set temperature, while Stove B required 5. That means either Stove B was tested at higher temps (to get a higher BTU tag) or Stove A does a better job keeping the heat away from the combustible surface or any other reason you can come up with. That being said, the numbers come from testing and not from using the dartboard method.

 

[JimWalshin845]

My hearth is about 6" shy of "minimum", and I don't quite have the "R" value given in the manual, but the hearth stays cool to the touch all of the time, even during big, hot fires, and even directly under the stove.

I think you are playing with fire. R value is just that resistance to heat. Correct code is 18" stove front to floor.

I think the stove fount to floor and hearth R value are set in stone for a safe operation. Stoves are UL tested that way any variation and you loose the UL safe install and you are not following the installation instructions, So you are also out of code .

Any stove related problems even ones not related to hearth or fount clearances and you just gave your insurance a out in a fire claim. Wood stove not installed to code, Wood stove not installed to manufactures instructions. Wood stove install dose meet UL standard. Claim denied.

I knew I was going to take heat on this one. I'm not advocating this; but it's what I have. There is a factor of safety built into this requirement, but regardless I know I SHOULD meet it. I know what R value is, I know (I think I know) the intention behind the minimum hearth distances. Fact of the matter is, when the stove's roaring hot, the floor is cold or cool to the touch all around and under the stove.

SO...what is the intention/safety concern with the min R value between stove/combustibles and the minmum non-combustible hearth width requirements? Am I right that it is for stray embers or logs falling out? You'll note that the requirement on non-loading door sides are considerably less than where the loading door is. And Again, the entire hearth is cool to the touch when the stove is at maximum temp. I really don't need to hear what a moron or criminal I am for not having a hearth up to code again, I just want to hear the reason behind the numbers...if I understand the rationale correctly, then I'm comfortable with my setup.

Sometimes safety has to do with things you can't see either:

Be safe... not sorry,
Jim