We are installing an Enviro free standing 1200 wood stove in our cabin in northern Minnesota. we know we have to create the noncombustible wall for this stove and am wondering if anyone as heard of using tempered glass mounted with an airspace behind as am acceptable wall?
non combustible wall
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a non combustible against a combustible wall with a 1" airspace gives you a 2/3 reduction in the listed clearance, but no less then 12". Glass is a non combustible.
Stoves are either listed for clearances, or there old and not listed. IF there NOT listed, the NFPA211 states that you need to be 36" from any combustible. If they are listed, the clearances will be on the back plate of the stove. These clearances are to combustibles. The heatsheilding rule stated above will apply. If you have a non combustible wall, a truly non combustible wall is non combustible from inside to the outside, counting trim, studs, finishing materials etc.
Stoves are either listed for clearances, or there old and not listed. IF there NOT listed, the NFPA211 states that you need to be 36" from any combustible. If they are listed, the clearances will be on the back plate of the stove. These clearances are to combustibles. The heatsheilding rule stated above will apply. If you have a non combustible wall, a truly non combustible wall is non combustible from inside to the outside, counting trim, studs, finishing materials etc.
Interesting thought... although that glass is non combustible, it will still allow for radiant conduction through to the combustible wall behind it. I'm not sure exactly of the conduction of tempered glass at the frequencies we're concerned with here, but - either it will allow it to radiate through, in which case it won't act as a heat shield and protect the wall behind it (so it functionally won't do any good for reducing clearance) OR it may absorb that energy and get really hot so make some good allowance for expansion of that glass as it heats up. Then again, it could reflect it all right back at you which would be really nice... Ok - I have no idea, but it is an interesting idea to think about, it might look really nice, but I'd want to be sure it was safe.
NFPA 211 does not give any guidelines as far as the non combustible r value or thickness, at least not that i remember. You can have glass hearthpads, why not heat shields? Durarock has a terrible r value, so does glass. its the air circulation behind the non combustable that gives it its r value. The wall shield needs to be open at the bottom and the top to allow proper circulation.
I do find it interesting that you can have glass hearthpads - do they qualify to protect against heat transmission or just ember protection? As to r value and durarock - at least it stops radiant energy when used as a heat shield.
What I'm thinking though is that in most cases the shielding in front of that 1" air gap is generally not going to allow direct transmission of the radiant energy. Perhaps I'm over thinking this (I have been accused of this habit before) but given the basics "Conduction, Convection, Radiation" transmission paths of heat energy - the "r value" only generally applies to the conduction value I believe. The air gap puts in a convection corridor so that heat actually gets carried away (dead air would have a specific r value since it would warm up and then conduct heat across the barrier). Some heat gets radiated across a gap - the shielding will warm up and start radiating heat out and across, but again - unless the shielding gets very hot, I expect this becomes somewhat immaterial for the purposes of the calculations.
So I come back to the question of "what if the shielding layer doesn't stop the radiant energy from the stove?" This would then strike the combustible surface behind the shielding and then heat that surface. It may all be moot - any tempered or other glass type of material that would be suitable for placing that close to a stove may actually either absorb or reflect the wavelengths that are carrying this energy.
Could the fact glass as a heat shield for a wall isn't covered in NFPA simply mean that it wasn't considered?
What I'm thinking though is that in most cases the shielding in front of that 1" air gap is generally not going to allow direct transmission of the radiant energy. Perhaps I'm over thinking this (I have been accused of this habit before) but given the basics "Conduction, Convection, Radiation" transmission paths of heat energy - the "r value" only generally applies to the conduction value I believe. The air gap puts in a convection corridor so that heat actually gets carried away (dead air would have a specific r value since it would warm up and then conduct heat across the barrier). Some heat gets radiated across a gap - the shielding will warm up and start radiating heat out and across, but again - unless the shielding gets very hot, I expect this becomes somewhat immaterial for the purposes of the calculations.
So I come back to the question of "what if the shielding layer doesn't stop the radiant energy from the stove?" This would then strike the combustible surface behind the shielding and then heat that surface. It may all be moot - any tempered or other glass type of material that would be suitable for placing that close to a stove may actually either absorb or reflect the wavelengths that are carrying this energy.
Could the fact glass as a heat shield for a wall isn't covered in NFPA simply mean that it wasn't considered?
Glass hearth pads are for ember protection only.
Wall heat shields can be made of sheetmetal which I would think to be more conductive than glass. My main concern about glass would be breakage by a falling hearth tool or perhaps during flue cleaning.
Wall heat shields can be made of sheetmetal which I would think to be more conductive than glass. My main concern about glass would be breakage by a falling hearth tool or perhaps during flue cleaning.
Im not sure why NFPA has not addressed this, but tempered glass does a pretty good job of blocking IR radiation. The hearthpads are only used for the stoves that call out for ember protection only. Im not a engineer by long shot, but dont most materials transmit infrared radiation? Is this the reason that IR remotes work through walls? I have no idea, just showing my stupidity.
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