Soot Mystery: Uncovering the Puzzling Phenomenon in a Wood-Burning Stove Room

In summary, the soot markings are most likely due to poor insulation or the use of a wood burning stove. The markings coincide with studs and are more likely to happen where there is a gap between the studs rather than on the studs themselves. There is no definite answer, but the thermal explanation seems most likely.
  • #1
DaveC426913
Gold Member
22,443
6,109
OK fizziks guys, here's a puzzle.

Took this pic at a friend's house today. They have a wood-burning stove in the room. The ceiling and wall are blackened with soot where ever there is a stud. I can't think of any explanation.

Some deets:
- the room is a closed-in porch, probably uninsulated or at least poorly-insulated
- there's a wood-burning stove just to the left of the pic. It's been in the house for decades.
- those soot-markings are quite clearly coinciding with studs. They're 16 inches apart and have cross braces.

Why would soot prefer to settle on the walls only where there is a stud behind it?
 

Attachments

  • soot.jpg
    soot.jpg
    20 KB · Views: 548
Physics news on Phys.org
  • #2
I can't think of any electrostatic reason.

Thermal conduction through the wall is higher where the studs are. Are these studs in outside walls?
 
  • #3
Bob S said:
I can't think of any electrostatic reason.

Thermal conduction through the wall is higher where the studs are. Are these studs in outside walls?
Yes. It's an enclosed porch. Roof and walls are exposed.

I am dubious about your assertion that the studs are better conductors of heat that the gaps between them. I know 4 inches of air is a good insulator, but so is 4 inches of wood.

That being said, my best hypothesis is also that it has something to do with heat differential, I think the air gaps will be colder. Though I don't know how that would result in the observed phenom.
 
  • #4
I agree that the air gaps should probably be colder, unless there is some insulating material in there.

Could it be related to humidity? The wooden studs might be prone to absorb humidity, whereas the air gaps, if ventilated, would dry out better.
 
  • #5
Are you sure (have you verified) those darkend areas are indeed accumulations of soot?
Could they be discolorations from some other cause?
 
  • #6
I think the thermal reason is the one to go for. But, rather than conductivity, I think it must involve thermal capacity. The areas attached to the studding will change temperature slower than the bits in between. Hence the temperature will be more different from that of the air beneath for longer. After the fire has been lit, the resulting differential temperature lag could produce more condensation of water vapour or, probably more importantly, condensation of oils, distilled from the burning wood. This would then tend to collect more dust, tar and soot particles over the years. There is always more smoke in the room just after a fire has been lit because the chimney has not yet started to 'draw' well so this period would be when there is more grot in the air and also when the temperature differential is greatest.
 
Last edited:
  • #7
sophiecentaur's explanation sounds entirely reasonable to me.
 
  • #8
Since it is DaveC, I will offer the following observations:

1) It is not actually the stud lines that are showing, that is coincidental. The boards are, of course, nailed at the studs, not in between.

2) The marking actually outlines the ceiling boards as can be seen from the transverse markings as well as the longitudinal ones. There may well not be any studs behind these transverse markings.

3) There is likely some material property of the joint filler used between the boards that is causing this. It may have become deliquescent.

go well
 
  • #9
@studiot
There isn't a lot of point in speculating about the construction - the true facts are available and Dave could help us with that (I thought he already had). But, the separation between the lines on walls and ceiling are much much more like stud and joist separation than standard plasterboard size (900mm X 1200mm). Plasterboard joints aren't usually a problem when taped and skimmed correctly.

If we're looking for a non-thermal explanation then wallpaper width would seem to be about right for the pattern. But the lines are too thick and even, I think, to be due to 'chemicals' at the seams.

If it has to be chemical then perhaps the timber for the studs was treated and the treatment chemicals are leaching out into the board. The actual colouration could still be largely due to stuff in the air ending up in some areas more than others. Are they smokers? - I remember people used to need their rooms redecoratied very frequently when everyone smoked in a household.
 
  • #10
I can think of two possible reasons. The first belongs to sophie already and is most likely correct, given the probable lack of insulation. The studs would act like cold plates used in oldtime fruit cellars to control humidity, water vapor condenses on those areas and the soot sticks . The second could be a moisture behind the walls condition. Drywall manufacturers now produce water and mold resistant products to combat this problem in high moisture areas. Are the surfaces painted with a latex or oil based paint? Wallpaper? The situation could be hazardous if the soot is in fact black mold. The reason the mold would grow in a pattern matching the studs is because the studs behind the walls are absorbing water from a leak/improper venting ect. and the moisture is wicking from the wood into the drywall. This could be the case given the conditions of the structure. Poor or no insulation, converted porch with no heating or cooling system, 5 outside walls(alot of surface area for water to leak through in the rain), there could also be a leak in the vent pipe (combustion of materials usually produces CO2 and h2o).
 
Last edited:
  • #11
Studiot said:
Since it is DaveC, I will offer the following observations:

1) It is not actually the stud lines that are showing, that is coincidental. The boards are, of course, nailed at the studs, not in between.

2) The marking actually outlines the ceiling boards as can be seen from the transverse markings as well as the longitudinal ones. There may well not be any studs behind these transverse markings.

3) There is likely some material property of the joint filler used between the boards that is causing this. It may have become deliquescent.

go well

It would be insanity to cut the panels in such tiny pieces.
1] Each panel would be 16 inches wide.
2] They would have to have been cut to different lengths, since the horizontal lines are not aligned. One might be 3 feet up, then the next might bw 5 feet up. This may not be readily apparent in the pic. But I noted it explicitly.

No, they are most certainly studs, not panel edges.
 
  • #12
My first thought was of a more mechanical nature. Soot is made up of fine particulate matter. Ambient noise may cause slight vibration of the drywall which essentially shakes off some of the particulates. Along the lines where the drywall is nailed to the studs it responds less to ambient vibration.
 
  • #13
Whatever is going on, insulating with a proper moisture barrier [facing] inside is almost certainly the appropriate solution.
 
  • #14
mrspeedybob said:
My first thought was of a more mechanical nature. Soot is made up of fine particulate matter. Ambient noise may cause slight vibration of the drywall which essentially shakes off some of the particulates. Along the lines where the drywall is nailed to the studs it responds less to ambient vibration.

I like this explanation.
 
  • #15
mrspeedybob said:
My first thought was of a more mechanical nature. Soot is made up of fine particulate matter. Ambient noise may cause slight vibration of the drywall which essentially shakes off some of the particulates. Along the lines where the drywall is nailed to the studs it responds less to ambient vibration.
I'm not sure the boundary conditions would be right to explain the positions and shapes of the patterns. You' d be needing suitable solutions to the wave equation for rectangular vibrating plates and I don't think the normal modes would support those particular shapes. Also, I think the residents would be wearing ear protectors. Haha.
 
  • #16
I do like mrspeedybob's approach to it, although I don't think its applicable in this situation.
 
  • #17
DaveC426913 said:
Yes. It's an enclosed porch. Roof and walls are exposed.

I am dubious about your assertion that the studs are better conductors of heat that the gaps between them. I know 4 inches of air is a good insulator, but so is 4 inches of wood.

That being said, my best hypothesis is also that it has something to do with heat differential, I think the air gaps will be colder. Though I don't know how that would result in the observed phenom.

Is this in Toronto? I see that you have 3 months of sub-freezing weather during the year. This might be a clue.

And I disagree with you that 4 inches of air is a good insulator. 4 inches of unobstructed air is horrible insulator. There's a reason most thermal pane windows have a 0.6" gap between the panes.

And wood kind of sucks as an insulator also. 0.7 - 1.4 R per inch? That's an R value of 4.9 at best for a 2x4. Nearly 3 times the conductance of my R-13 wall insulation.

I've a wood burning Franklin stove in my living room (they leak like a sieve!), that I've used for almost 20 years during the winter, and I've no such lines on my ceiling or walls.

With so few clues/parameters, it's difficult to deliver little more than a hypothesis.

Mine is that the ceiling and walls do contain insulation, and the thermal conductance of the studs is causing cold spots, which leads to condensation [STRIKE]points[/STRIKE] lines, which leads to soot lines. (In agreement with Sophie and the Jedi's choices, as far as I can tell.)

or perhaps it's not soot at all... perhaps it's the Black Death!

My entire bathroom is covered in that stuff... :redface:
 
  • #18
For a while this winter, I lived in a place where i could look across the street and see a sloped shingled roof (facing east), which usually accumulated a heavy frost every night. The morning sun would hit the roof by about 7:30 am. By about 8 or 9 am, I could see clear lines on the roof where the frost has sublimed. These lines appeared to be directly above roof joists. It wasn't clear whether the frost sublimed because of a heat leak, or because of stored heat capacity in the joists themselves.
 
  • #19
sophiecentaur said:
mrspeedybob said:
My first thought was of a more mechanical nature. Soot is made up of fine particulate matter. Ambient noise may cause slight vibration of the drywall which essentially shakes off some of the particulates. Along the lines where the drywall is nailed to the studs it responds less to ambient vibration.
I'm not sure the boundary conditions would be right to explain the positions and shapes of the patterns. You' d be needing suitable solutions to the wave equation for rectangular vibrating plates and I don't think the normal modes would support those particular shapes.
sophie, you may be overthinking it. It wouldn't have to be standing or resonant waves. It is plausible that the panels where they are secured to the joists will tend to shake less than anywhere else.
OmCheeto said:
Is this in Toronto? I see that you have 3 months of sub-freezing weather during the year. This might be a clue.
Yes, but how?
OmCheeto said:
And I disagree with you that 4 inches of air is a good insulator.
That's what BobS was claiming. He suggested conduction is better through the studs than through the air:
Bob S said:
Thermal conduction through the wall is higher where the studs are.

Bob S said:
For a while this winter, I lived in a place where i could look across the street and see a sloped shingled roof (facing east), which usually accumulated a heavy frost every night. The morning sun would hit the roof by about 7:30 am. By about 8 or 9 am, I could see clear lines on the roof where the frost has sublimed. These lines appeared to be directly above roof joists. It wasn't clear whether the frost sublimed because of a heat leak, or because of stored heat capacity in the joists themselves.
Yes. I think thermal conduction is surely the key to this. But snow is one thing, soot is another.

I see two outstanding questions:
1] Are the studs going to be warmer than the air or vice versa? Or is there a more complex reaction occurring over time?
2] How does thermal change result in changes in soot accumulation?
 
Last edited:
  • #20
If for whatever reason the panels are colder above the studs, then you'd expect these areas to condense more moisture (or volatiles evaporated from the fire). Soot would in turn stick to that. Sophie already pointed that out.

However, I believe that 4 inches of air would conduct more heat than wood, due to convection.
 
  • #21
M Quack said:
If for whatever reason the panels are colder above the studs, then you'd expect these areas to condense more moisture (or volatiles evaporated from the fire). Soot would in turn stick to that. Sophie already pointed that out.

However, I believe that 4 inches of air would conduct more heat than wood, due to convection.

Yes. I believe the air gaps will conduct more heat (and thus feel colder) than the studs. That's also why bridges ice over before level roads. There's no heat capacity in air.

Unfortunately, that gets us the wrong answer, since it leads to the conclusion that more moisture would condense on the colder surfaces i.e. between the studs.
 
  • #22
I think you are ignoring heat capacity and what happens during fast temperature changes.

I've just been watching Silent Witness...
 
  • #23
sophiecentaur said:
I think you are ignoring heat capacity and what happens during fast temperature changes.
I'm all ears.
 
  • #24
I think Bob S is on the right track. Materials can collect soot deposits because they are cooler or have higher moisture content. It’s commonly known that thermophoresis can contribute to soiling of wall surfaces over studs and air conditioning vents.
 
  • #25
SecularSanity said:
I think Bob S is on the right track. Materials can collect soot deposits because they are cooler or have higher moisture content. It’s commonly known that thermophoresis can contribute to soiling of wall surfaces over studs and air conditioning vents.
Hm OK. Thermophoresis lends a plausible explanation as to why the soot would collect on a cooler area.

But, why would the studs cause the panels nearby to
- be cooler
or
- have higher moisture content?
 
  • #26
DaveC426913 said:
I'm all ears.

Look at my earlier post. High thermal capacity means temperature lag. So condensation when the fire is lit and water is produced on cooler surfaces from combustion, perhaps - or drying socks.
 
  • #27
sophiecentaur said:
High thermal capacity means temperature lag. So condensation when the fire is lit ...
Ah. I get it now. Thanks.
 
  • #28
DaveC426913 said:
Hm OK. Thermophoresis lends a plausible explanation as to why the soot would collect on a cooler area.

But, why would the studs cause the panels nearby to
- be cooler
or
- have higher moisture content?

Well, you said that it was blackened with soot where ever there is a stud, right? Doesn’t hygroscopic behavior of the wood stud lead to higher moisture contents?

Just Google soot deposition by thermophoresis, and maybe temperature gradient in studs in the wall.
 
  • #29
Exactly the same happens in my house. At the moment these darker lines are hardly visible, as we painted walls two years ago and they are becoming obvious after 3-4 years. Yes, they are on studs for sure, I have checked it personally, no they have nothing to do with the places where panels merge (although for obvious reasons panels meet on some of the studs).

One additional observation - panels are attached to the studs with screws, and the places where the screw heads are below the plaster and the paint are pretty well marked with even darker spots.
 
  • #30
Bob S said:
For a while this winter, I lived in a place where i could look across the street and see a sloped shingled roof (facing east), which usually accumulated a heavy frost every night. The morning sun would hit the roof by about 7:30 am. By about 8 or 9 am, I could see clear lines on the roof where the frost has sublimed. These lines appeared to be directly above roof joists. It wasn't clear whether the frost sublimed because of a heat leak, or because of stored heat capacity in the joists themselves.
I am fairly sure these roofs were insulated with fiberglass bats, with perhaps R-23 to R-30 insulation rating.
 
  • #31
DaveC426913 said:
...

OmCheeto said:
Is this in Toronto? I see that you have 3 months of sub-freezing weather during the year. This might be a clue.
Yes, but how?

Like I said, I've been using my wood stove for 20 years and have never seen such a thing. It's been at least 15 years since I've painted, and there is absolutely no indication of such marks on my peripheral walls.

Comparing temperatures of a few of the responders:

pf.ave.monthly.temps.jpg


It's obvious that you've got the highest temperature gradient in the winter. And if that really is just an enclosed porch who's only heat source is the wood stove, the studs are going to be ice cubes if the fire goes out. And as SophieC stated, their heat capacity is going to cause them to take a lot longer to warm up.

I see two outstanding questions:
1] Are the studs going to be warmer than the air or vice versa? Or is there a more complex reaction occurring over time?
2] How does thermal change result in changes in soot accumulation?

I'm going to go out on a limb and state that I'm 99% positive that the walls and ceilings are insulated, and the soot is a result of studs being the cold spot.

Borek's January temperatures, and observations regarding the screws, seem to support the hypothesis.

I would make a joke about the studs sucking the thermal energy from the room like a vacuum cleaner, and carrying the soot along with it, but that would be silly.
 
  • #32
OmCheeto said:
It's obvious that you've got the highest temperature gradient in the winter.
To be clear, I was not doubting the temp gradient. I am well aware of it; I just was having trouble connecting the dots about how that lead to the observed phenom.


I think the biggest difficulty I've been having is that I've been intuitively assuming that it would be warmer under the studs than elsewhere. But if it's actually colder under the studs - especially during the initial fire-starting phase when soot emission is highest - then the rest makes sense.

Thanks guys.
 
  • #33
I still wonder whether what you are seeing is actually just 'soot'. I think it's more likely to include tar (sticky) - like you get with cigarette smoke.

Next time you go round, you need to offer to clean their ceiling and walls and see whether you need detergent to shift the marks.
 
  • #34
Ok, the stove is only lit in cold weather. I am assuming that the porch room does not have a connection to the household heating system. Assuming these, I feel safe saying that the studs, drywall, air behind the walls, furniture ect... Have all reached thermal equalibrium as a system. Lighting a fire rapidly heats the room air. That heat is then transferred to all the surrounding matter through the usually channels. All the materials that are in contact with the air are going to warm at different rates. The studs are connected to another wall, the outside one. If the air temp outside is cold enough, I'd think under 50f, then the studs simply take longer to warm. Wood is a great insulator, but it also contains water and retains the ability to absorb it even in the afterlife. This could skew the woods heat capacity. The wooden studs absorb the heat that the drywall (at the point of contact) is absorbing. Depending on the conditions, it is plausible that the studs could take a significant amount of time to heat, and until they reach equalibrium they will continue to act like moisture magnets.
 
  • #35
Does the wall facing the house suffer the same soot lines? I am assuming the outside wall of the house that the porch is attached to in the porch room was not significantly reconstructed when the room was converted. I wouldnt. This means that the porch room is probably insulated from the rest of the home but those studs (likely connected to an inside wall) would not be subject to soot accumalation.
 
<h2>1. What is soot and why does it form in a wood-burning stove room?</h2><p>Soot is a black, powdery substance that is formed when organic matter, such as wood, is burned incompletely. In a wood-burning stove room, soot can form due to a lack of oxygen or improper ventilation, which prevents complete combustion of the wood.</p><h2>2. Is soot harmful to human health?</h2><p>Yes, soot can be harmful to human health if inhaled. It contains small particles that can irritate the respiratory system and may also contain toxic chemicals. It is important to properly ventilate wood-burning stove rooms and regularly clean out any built-up soot to prevent potential health risks.</p><h2>3. How can I prevent soot from forming in my wood-burning stove room?</h2><p>To prevent soot from forming, it is important to properly maintain your wood-burning stove. This includes regularly cleaning out any built-up soot and making sure the stove is getting enough oxygen for complete combustion. It is also important to use dry, seasoned wood and avoid burning materials that produce a lot of smoke.</p><h2>4. Can soot be removed from surfaces in a wood-burning stove room?</h2><p>Yes, soot can be removed from surfaces in a wood-burning stove room. It is best to use a dry cloth or vacuum to remove loose soot particles, and then use a mild soap and water solution to clean any remaining residue. It is important to wear gloves and a mask when cleaning up soot to avoid inhalation.</p><h2>5. Are there any other potential dangers associated with soot in a wood-burning stove room?</h2><p>Aside from potential health risks, soot can also be a fire hazard. It can build up in the chimney and flue, increasing the risk of a chimney fire. It is important to regularly clean and inspect the chimney and flue to prevent this danger. Soot can also stain walls, furniture, and other surfaces, so it is important to clean it up promptly to avoid permanent damage.</p>

1. What is soot and why does it form in a wood-burning stove room?

Soot is a black, powdery substance that is formed when organic matter, such as wood, is burned incompletely. In a wood-burning stove room, soot can form due to a lack of oxygen or improper ventilation, which prevents complete combustion of the wood.

2. Is soot harmful to human health?

Yes, soot can be harmful to human health if inhaled. It contains small particles that can irritate the respiratory system and may also contain toxic chemicals. It is important to properly ventilate wood-burning stove rooms and regularly clean out any built-up soot to prevent potential health risks.

3. How can I prevent soot from forming in my wood-burning stove room?

To prevent soot from forming, it is important to properly maintain your wood-burning stove. This includes regularly cleaning out any built-up soot and making sure the stove is getting enough oxygen for complete combustion. It is also important to use dry, seasoned wood and avoid burning materials that produce a lot of smoke.

4. Can soot be removed from surfaces in a wood-burning stove room?

Yes, soot can be removed from surfaces in a wood-burning stove room. It is best to use a dry cloth or vacuum to remove loose soot particles, and then use a mild soap and water solution to clean any remaining residue. It is important to wear gloves and a mask when cleaning up soot to avoid inhalation.

5. Are there any other potential dangers associated with soot in a wood-burning stove room?

Aside from potential health risks, soot can also be a fire hazard. It can build up in the chimney and flue, increasing the risk of a chimney fire. It is important to regularly clean and inspect the chimney and flue to prevent this danger. Soot can also stain walls, furniture, and other surfaces, so it is important to clean it up promptly to avoid permanent damage.

Back
Top