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Truecabin
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# Posted: 27 Nov 2013 12:36pm
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i put a thin sheetmetal under the stove just so i could use the stove then planning to make a hearth of brick someday but the metal never got even warm after many hot fires over the years
if i burn a hot fire for days the floor never gets hot not even warm
the floor is wood insulated r19 and these are hot fires some days the wall gets too warm
my stove has an under heat shield about an inch below if you have a heat shield maybe you dont need brick
those of you with a hearth of brick or stone does it ever get hot even warm because my metal is always cold wet boots below stay wet I cant dry shoes below the stove
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MtnDon
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# Posted: 27 Nov 2013 12:54pm - Edited by: MtnDon
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There are two reasons for a non combustible hearth. Radiant heat protection and embers. Most stoves today come with a bottom heat shield; at least the good ones I've looked at do. May be an option on some. That will usually keep the floor protected from heat radiating from the bottom. But there is still the potential issue of embers that may fall and not be noticed when loading more fuel.
If your stove does not radiate much heat out the bottom that is probably good, IMO.
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Martian
Member
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# Posted: 27 Nov 2013 01:07pm - Edited by: Martian
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I have a cheap stove in the shop...no heat shield. Like yours, it sits on a piece of thin sheet metal to catch the embers. The metal never becomes warm, much less hot.
Tom
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SandyR
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# Posted: 27 Nov 2013 01:44pm
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We have no heat shield. Our large wood stove in our regular home heats all of the bricks that it sits on. We are able to dry all of our wet boots and mittens under it.
It would really be a hardship if I wasn't able to dry things under it in the winter.
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Truecabin
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# Posted: 27 Nov 2013 03:30pm
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my house has a big hearth built up above the floor it makes the stove a permanent fixture but it is nice because the stove is raised 6 inches
but it would be ugly if no stove and i bet it cost a lot
so if the stove has a heat shield or if you add a heat shield then i think you dont have to worry much about the floor this can help in a small cabin
you will know if your floor is cold after a long hot fire then think about other fire safety concerns you dont have that problem
Quoting: MtnDon But there is still the potential issue of embers that may fall and not be noticed when loading more fuel.
i hear that make the stove safe for people who dont know how to use a stove because you cant watch people every minute
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OwenChristensen
Member
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# Posted: 27 Nov 2013 06:31pm
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Yes, heat rises. If you had no ashes there would be some heat below.
O
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bldginsp
Member
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# Posted: 28 Nov 2013 11:57am
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From reading about how radiant heat barriers work in attics, the heating and insulation gurus describe three kinds of heat- radiant, conductive, and air borne (I think that's it...) Radiant is what you feel with your hand a foot from the stove, conductive is what burns your hand when you touch something that got exposed to heat and conducted it, like the end of a metal rod in a fire, and air borne is just how hot the air itself gets.
Hot air goes up, but radiant and conductive heat do not. Radiant radiates in all directions, conductive follows the path of least resistance along a given material.
The bottom of a wood stove will radiate heat, and a heat shield will reduce that. But radiated heat that hits a reflective material beneath may well just reflect away- that's what a radiant barrier in an attic does. Conductive and air borne heat will still cause the metal to heat, but as the stove heats the air around it, it creates upward convection that will draw lower, cooler air in the room toward the bottom of the stove, cooling the sheet metal.
Brick or stone, on the other hand, are not reflective and will be heated by radiant heat from the stove. If exposed over a long time without enough clearance they will continue to heat up, and since they are conductors they will heat what's behind. Sheet metal under the brick will not reflect away the heat if there is no air space between it and the brick, so the metal would just conduct the heat straight thru to what's below. Experience seems to show this isn't a problem below a stove on correct legs, but is a serious issue on the walls. That's why any metal or brick used on the walls needs to be spaced out from the wall an inch or so if it is used to reduce clearance to combustibles.
I agree with MtDon that the reason to put down sheetmetal on your wood floor is to prevent embers from directly contacting the wood, even though if a substantial quantity of embers touched the metal it would conduct the heat straight thru and cause a fire. So maybe that's why you put brick on the metal on the floor, to keep large amounts of embers off the metal.
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Truecabin
Member
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# Posted: 28 Nov 2013 04:59pm - Edited by: Truecabin
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if wood can ignite at 215deg or 250 this would be a lot bigger problem everybody would know and it would be in the code
could be something else maybe bugs wings or spiderwebs who knows
not sure how this applies to cold wood or cold steel
bldginsp i can see you are looking for the word convective not air born
but do you really mean this
Quoting: bldginsp if a substantial quantity of embers touched the metal it would conduct the heat straight thru and cause a fire.
not enough heat in an ember the steel will stay cold but i guess it depends what you mean by ember 
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MtnDon
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# Posted: 28 Nov 2013 05:51pm
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Quoting: Truecabin if wood can ignite at 215deg this would be a lot bigger problem not just one place on the internet
No "if" and not just one place on the internet. I took the quick and dirty way to point to a link, one I knew about. For anyone who is doubtful take a moment and Google "pyrolization of wood". Lots of other search results will appear. It is not some sort of voodoo. That is not to say that we are going to find ourselves with mysterious fires breaking out all over the place. many improperly installed wood burning devices don't get used enough to have a fire actually occur.
Quoting: Truecabin not sure how this applies to cold wood and cold steel
Somehow it came up with a little thread drift, not an uncommon thing, more frequent than mysterious fires.
Gotta turkey to eat.
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bldginsp
Member
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# Posted: 28 Nov 2013 06:02pm
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Truecabin- what they say is that when the wood is exposed to high heat for long periods of time, it's ignition temperature gradually drops down to a very low level. So the wood trim on the window next to your stove which gets hot every time you use the stove, gradually lowers its ignition level. So they say.
By a substantial number of embers i mean a small pile of coals dumped on the sheet metal. The metal will transfer the heat right thru. Unlikely circumstance but possible.
Yes I meant convective not air born. Thanks.
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bldginsp
Member
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# Posted: 28 Nov 2013 06:11pm
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Incidentally Truecabin it is in the code, more or less. That's a part of the reason for clearance to combustibles
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Dekagoldwingers
Member
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# Posted: 13 Dec 2013 12:33pm
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I used to be a fire investigator in a former life! It is very true that wood subject to extended exposure to temps in the range of 200 to 250 F. Will develop a reduced ignition temperature. I investigated a number of fires where that process was involved. The only thing that protects against heat transfer is distance and the proper kind of insulation (not fibreglass) you can cut down on distance by doing things like placing a heat guard of steel that has a defined air space on each side. For instance, a steel sheet with 1" air gap, can cut required clearance from 18" to 9". The steel does not need to be on the exposure, can be on the appliance. Any proper appliance will have the required clearances labeled on it. The exposure from bare stove pipe is 18" in all directions at a bare minimum.
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MtnDon
Member
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# Posted: 13 Dec 2013 01:37pm
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Dekagoldwingers thank you 
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Truecabin
Member
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# Posted: 13 Dec 2013 04:22pm
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yes deka i understand heat shields the shield is at a lower temp because it radiates half back to the stove and that lower temp on the backside has a reduced distance
i said above i have a steel heat guard on my stove bottom but its a half inch from the stove and i think its good
but back to subject of this thread under stove is always cold even with hot fire when i have to dry my shoes i put them by the fridge not by my stove because its much warmer by the fridge and theres no danger and even less danger under the stove because we are talking about cold not 200deg
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