At what temp does wood ignite?

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Cudos

Member
Aug 11, 2009
107
Central Alberta
I have a PE super27 that was installed on a proper hearth and proper specs in relation to the surrounding walls (bare tongue & groove spruce). The stove is in a corner and the distances from the back corners of the stove are within PE safety requirements.

Now I have taken the temps of the wood with an IR gun at the rear corners where it gets hottest with the stove at max operating temps. These temps are usually around 110 - 131F. Is it true that the ignition point of wood is around 500F. While the walls feel quite warm they are not overly hot to the touch. Being bare wood should I cover them, even though they are the proper distance away from the stove.?

Thanks.
 

HotCoals

Minister of Fire
Oct 27, 2010
3,429
Rochester,Ny.
I don't think anyone is going to answer that question.
What if some one said you're fine but a month latter your house catches on fire.
Safety first is how I would respond.
 

Cudos

Member
Aug 11, 2009
107
Central Alberta
HotCoals said:
I don't think anyone is going to answer that question.
What if some one said you're fine but a month latter your house catches on fire.
Safety first is how I would respond.
I'm looking for opinion and experience here. You obviously don't know, which is fine, but implying no one will have an opinion is premature in my mind. Its a fair question, at what temp does wood ignite, regardless of my setup.
 

Joe Matthews

Member
Sep 2, 2010
80
Raleigh NC
Your question does have many variables. To answer a direct question with a direct answer, the flash point of wood is generally considered to be appx 550 - 600 degrees F. But in real world terms, that would all depend on moisture content, humidity, type, coating (ie stain, paint etc.) You are not getting anywhere near that temp of course. The article posted above discusses how prolonged exposures to heat can lower the flash point of wood over time. This is the danger that requires the heat clearances to combustible materials. If they are exposed to temperatures high enough for a long enough time the flash point is lowered making the material easier to ignite should some unusual event happen like a chimney fire.
 

HotCoals

Minister of Fire
Oct 27, 2010
3,429
Rochester,Ny.
Cudos said:
HotCoals said:
I don't think anyone is going to answer that question.
What if some one said you're fine but a month latter your house catches on fire.
Safety first is how I would respond.
I'm looking for opinion and experience here. You obviously don't know, which is fine, but implying no one will have an opinion is premature in my mind. Its a fair question, at what temp does wood ignite, regardless of my setup.
I stand by my statement because you are actually talking about the probability of your wall catching on fire is what it comes down too.
Are you going to be there checking temps 24/7?
It's in your head now that it might not be all that safe...and you might be right.
I would think you want someone who is a expert at theses things to look it over if concerned at all of the possibility of a house fire.
 

BrotherBart

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Cudos

Member
Aug 11, 2009
107
Central Alberta
Thank-You everyone, I have read the link and wow, the variables are indeed many. While I appear to well under the threshold for combustion I now realize that things can change over time. As I am only burning on weekends and in the winter I have some time to look at this. Yes safety first, so I may just add some comfort layering just to be sure. I really thought it was just a case wood gets hot enough then ignites, not realizing that it may be a progressive threat as time and wood characteristics change.

Thanks all for your input.
 

soupy1957

Minister of Fire
Jan 8, 2010
1,365
Connecticut
www.youtube.com
Someone in here had told me some time ago, that surrounding materials need to be at least 450ºF before there is a danger of spontaneous combustion (which is really what we're talking about, since I'm making the assumption that you are not asking if a hot ember can ignite surrounding material).

I use that as a baseline, in my consideration of things, and realize of course that it would take full direct exposure to open flame, to get the surrounding materials to that temp.. (which is why "closing the door" of the stove is such a good thing!! lol)

-Soupy1957
 

Danno77

Minister of Fire
Oct 27, 2008
5,008
Hamilton, IL

Battenkiller

Minister of Fire
Nov 26, 2009
3,739
Just Outside the Blue Line
Danno77 said:
the autoignition of wood is something I've explored quite a bit, just because I like to know stuff and the scientific stuff I found on the topic is kinda neat.

Here are two things that I have bookmarked, but googling some keywords will lead you to more stuff.

http://marioloureiro.net/ciencia/ignicao_vegt/wood_ign.pdf (I love this one)
http://www.waset.org/journals/waset/v47/v47-13.pdf (a good one, too)
Very good stuff, Danno.

Both of these papers are bring up the concept of heat flux. That's what you need to be concerned about with wood stoves. Big stoves put out proportionally more heat at the same temperature because they have larger radiating surface areas. In a nutshell, heat flux is what clearances are all about, not stove temps. You could hold a bright-red glowing poker (>1400ºF) 6" away from a wooden wall for months and it wouldn't ignite the wood because the heat flux is too small due to its extremely small radiating surface area.
 

Jags

Moderate Moderator
Staff member
Aug 2, 2006
18,004
Northern IL
In a nut shell - UL standards allow for a 70-100F temp rise of surrounding walls over room temp. If you have a 70F room temp - you are allowed 140-170F wall temps and are still within the safety guide lines.
 

tfdchief

Minister of Fire
Nov 24, 2009
3,336
Tuscola, IL
myplace.frontier.com
Battenkiller said:
Danno77 said:
the autoignition of wood is something I've explored quite a bit, just because I like to know stuff and the scientific stuff I found on the topic is kinda neat.

Here are two things that I have bookmarked, but googling some keywords will lead you to more stuff.

http://marioloureiro.net/ciencia/ignicao_vegt/wood_ign.pdf (I love this one)
http://www.waset.org/journals/waset/v47/v47-13.pdf (a good one, too)
Very good stuff, Danno.

Both of these papers are bring up the concept of heat flux. That's what you need to be concerned about with wood stoves. Big stoves put out proportionally more heat at the same temperature because they have larger radiating surface areas. In a nutshell, heat flux is what clearances are all about, not stove temps. You could hold a bright-red glowing poker (>1400ºF) 6" away from a wooden wall for months and it wouldn't ignite the wood because the heat flux is too small due to its extremely small radiating surface area.
Time (duration of constant, extended radiation) is so important as well. When it gets cold and firing hard for extended periods of time, things happen that wouldn't otherwise.
 

polaris

Feeling the Heat
Jan 31, 2008
419
KY.
No wood could suffer auto ignition at 130 degrees. If it would there would not be a deck/roof left in the southwest. Not a particularly scientific theory but it does seem to be a matter of common sense(up to a point).
joe
 
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Battenkiller

Minister of Fire
Nov 26, 2009
3,739
Just Outside the Blue Line
tfdchief said:
Time (duration of constant, extended radiation) is so important as well.
Undeniably, time is extremely important because heat transfer is not instantaneous. However, it is the actual amount of heat transferred that is heating the exposed surfaces up, not the temperature of the radiating surface. Another example is an incandescent light bulb. The filament in a 100W light bulb is close to 5000ºF, but you can put a 100W light near a wall for a very long time and the wall will barely get warm. This is because the surface area of the radiating filament is so small it is negligible.

This is why bigger stoves put out more heat. It's not that they hold a larger charge (firebox size), it's that they have more surface area to get heated by that charge. At identical surface temps, a stove that has twice the radiating surface as a smaller stove will put out twice the heat at identical temperatures... not matter how much wood is in the box getting it there.
 

tfdchief

Minister of Fire
Nov 24, 2009
3,336
Tuscola, IL
myplace.frontier.com

begreen

Mooderator
Staff member
Nov 18, 2005
78,033
South Puget Sound, WA
Cudos said:
I have a PE super27 that was installed on a proper hearth and proper specs in relation to the surrounding walls (bare tongue & groove spruce). The stove is in a corner and the distances from the back corners of the stove are within PE safety requirements.

Now I have taken the temps of the wood with an IR gun at the rear corners where it gets hottest with the stove at max operating temps. These temps are usually around 110 - 131F. Is it true that the ignition point of wood is around 500F. While the walls feel quite warm they are not overly hot to the touch. Being bare wood should I cover them, even though they are the proper distance away from the stove.?

Thanks.
We have the Alderlea in a corner install and see the same temps. You are correct, wood ignites around 450F. Your walls are in no danger at those low temps and will be ok up to about 180F, and that is with a healthy margin of safety. Got hot water heat? Often those pipes pass in direct contact with wood with 180F water passing through them.

Enjoy the nice new stove and don't worry about the walls. As long as the stove was installed correctly, respecting the tested clearances, it will be fine.
 

CarbonNeutral

Minister of Fire
Jan 20, 2009
1,132
Nashoba Valley(ish), MA
tfdchief said:
Dakotas Dad said:
There is no set answer, lots of variables..

try here.. http://www.doctorfire.com/low_temp_wood1.pdf
This one really got me! I have been in the Fire Servie for 32 years and would never have thought this could happen from such a low heat source!
Yeah, I don't believe that paper - there must be something else at play - an isolated incident when millions of homes have hot water pipes passing through and touching wood.
 

r_d_gard

Member
Nov 9, 2009
124
Maryland - USA
www.cff.org
Cudos said:
I have a PE super27 that was installed on a proper hearth and proper specs in relation to the surrounding walls (bare tongue & groove spruce). The stove is in a corner and the distances from the back corners of the stove are within PE safety requirements.

Now I have taken the temps of the wood with an IR gun at the rear corners where it gets hottest with the stove at max operating temps. These temps are usually around 110 - 131F. Is it true that the ignition point of wood is around 500F. While the walls feel quite warm they are not overly hot to the touch. Being bare wood should I cover them, even though they are the proper distance away from the stove.?

Thanks.

Ignition temp of paper is 451°F, if that helps any
 

begreen

Mooderator
Staff member
Nov 18, 2005
78,033
South Puget Sound, WA
rayza said:
Ignition temp of paper is 451°F, if that helps any
Bradbury's book left that number permanently inscribed on my brain cells.
 

Battenkiller

Minister of Fire
Nov 26, 2009
3,739
Just Outside the Blue Line
polaris said:
No wood could suffer auto ignition at 130 degrees. If it would there would not be a deck/roof left in the southwest.
Ha, ha! True enough. Not just in the SW either. I was stunned to take an IR reading on my wood pile and found temps after only a few hours in full sun were in the upper 130s. This was in October. Can't imagine how hot that wood got during that hot, dry heat spell we had early this summer.

I'd have to say that if you are following the manufacturers clearances, I think you are probably safe for any normal (up to 750º) burn temps . Still, it makes you leery when just before you go to bed you point that laser dot at the low basement ceiling and those floor joists are 145º... in spite of the fact that you have exceeded the recommended clearances by a healthy margin.
 
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