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> rapidly and cleanly burn a large charge of wood I was under the impression wood-burning stoves produce very high amounts of particulate pollution, is “clean”

> rapidly and cleanly burn a large charge of wood I was under the impression wood-burning stoves produce very high amounts of particulate pollution, is “clean” really an accurate claim?

gjsman-1000 4y ago
Used to, not anymore. Old wood stoves produced as much as 50+g./hr. of particulate matter, current standards are 2.5g./hr. for cord wood for new EPA-certified wood stoves since 2015. Most masonry heaters constructed in the last 20 years are in the 1-3g/hr. range (and for this reason have never needed EPA certification).
cperciva 4y ago
I think "clean" is intended relative to other wood-burning stoves. Because this design of stove burns at relatively high temperature, it yields more complete combustion and emits lower levels of particulate.
- daneel_w 4y ago
  > " Because this design of stove burns at relatively high temperature, it yields more complete combustion and emits lower levels of particulate." This doesn't sound right to me, because there's heavy soot production whether hot or cold stove. Are you sure it's not just because a large masonry stove (and its long chimney) has a lot more surface for soot and particulate to stick on compared to e.g. a tiny portable one?
  - Ekaros 4y ago
    Not too much soot should be produced in well designed burning. Which includes sufficient input of oxygen. Ofc, also the material burned matters. Only untreated wood and with right moisture level. The emissions increase with both too wet and too dry wood.
    - bcbrown 4y ago
      How does too dry wood result in higher particulate emissions?
      - Ekaros 4y ago
        It burns too fast. I'm not entirely certain of mechanism, but it could break up and vaporize faster than wood with bit higher moisture content. The whole process comes back to sufficient supply of oxygen.
  - cperciva 4y ago
    Soot is amorphous carbon; that will absolutely be burned at higher temperatures (given sufficient oxygen). You might be thinking of ash, which consists mostly of inorganic residue (although even there you'll see carbonates at low temperatures and metal oxides at higher temperatures). But when we talk about burning wood cleanly we're really talking about smoke -- and that's almost entirely organics (including large amounts of carbon monoxide, methane, and VOCs) which will combust given sufficient heat and oxygen.
  - 2000UltraDeluxe 4y ago
    If you have a decent masonry stove, good airflow and dry firewood then most of the particles will simply burn. Once the stove is hot enough, the smoke will ignite and most of that soot is converted into heat and energy.
bcbrown 4y ago
Yes, it can be. By carefully designing the size of the various chambers in a stove, full combustion can be achieved such that the only byproducts are CO2 and H20. This does not happen in a conventional fireplace. Part of the motivating design goals for "rocket stoves" is to achieve this sort of complete combustion. If you're interested in the chemical and physical processes that comprise combustion, I cannot recommend the Faraday Lectures highly enough. Michael Faraday was an experimental physicist, and the data resulting from his experiments were what James Maxwell used to derive Maxwell's Equations for electromagnetic phenomena. Separately, he gave a lecture on candles and combustion, which has been recreated in the original language here: https://www.youtube.com/playlist?list=PL0INsTTU1k2UCpOfRuMDR-wlvWkLan1_r https://www.youtube.com/playlist?list=PL0INsTTU1k2UCpOfRuMDR.... The important intuition is that combustion is a gaseous process. When burning (solid) wood, the heated wood will give off gasses and particulate matter (soot). Those gasses and particulates will combine with gaseous oxygen in an exothermic reaction called combustion. In a conventional fireplace, the oxygen and temperature constraints result in incomplete combustion, leading to particulate pollution as you mention. The search term to learn more about overcoming those hurdles is "rocket stove". In these sorts of stoves, there's a few modifications that result in more-complete combustion. There's separate chambers for the wood and the combustion. In the first chamber, the same processes as in a conventional fireplace occur: the wood burns, creating soot and hydrocarbon gasses. In the second chamber, hot air is added to provide a secondary source of oxygen, and the airflow velocity is reduced (by carefully calculating chamber size using the Bernoulli fluid equation), resulting in complete combustion. By having a right angle between the input from the wood chamber and the chimney, you can achieve a chaotic mixing (in terms of chaos theory) between the wood byproducts and the added oxygen, which also helps ensure complete combustion. So the entire system has the following parts: a chamber to burn the wood; a chamber where hot external air is added and full combustion achieved; a tall chimney to ensure a good draft and airflow; a "bell" to slow air velocity of the hot exhaust and ensure good thermal transfer; a final exhaust port. Here's some resources: https://www.youtube.com/watch?v=IsO9vLn8JHw https://www.youtube.com/watch?v=IsO9vLn8JHw https://en.wikipedia.org/wiki/Rocket_mass_heater https://en.wikipedia.org/wiki/Rocket_mass_heater https://paulwheaton.com/efficient-wood-heat/ https://paulwheaton.com/efficient-wood-heat/ https://permies.com/f/260/rocket-mass-heaters https://permies.com/f/260/rocket-mass-heaters

> rapidly and cleanly burn a large charge of wood I was under the impression wood-burning stoves produce very high amounts of particulate pollution, is “clean” really an accurate claim?

gjsman-1000 4y ago

Used to, not anymore. Old wood stoves produced as much as 50+g./hr. of particulate matter, current standards are 2.5g./hr. for cord wood for new EPA-certified wood stoves since 2015. Most masonry heaters constructed in the last 20 years are in the 1-3g/hr. range (and for this reason have never needed EPA certification).

cperciva 4y ago

I think "clean" is intended relative to other wood-burning stoves. Because this design of stove burns at relatively high temperature, it yields more complete combustion and emits lower levels of particulate.

daneel_w 4y ago
> " Because this design of stove burns at relatively high temperature, it yields more complete combustion and emits lower levels of particulate." This doesn't sound right to me, because there's heavy soot production whether hot or cold stove. Are you sure it's not just because a large masonry stove (and its long chimney) has a lot more surface for soot and particulate to stick on compared to e.g. a tiny portable one?
- Ekaros 4y ago
  Not too much soot should be produced in well designed burning. Which includes sufficient input of oxygen. Ofc, also the material burned matters. Only untreated wood and with right moisture level. The emissions increase with both too wet and too dry wood.
  - bcbrown 4y ago
    How does too dry wood result in higher particulate emissions?
    - Ekaros 4y ago
      It burns too fast. I'm not entirely certain of mechanism, but it could break up and vaporize faster than wood with bit higher moisture content. The whole process comes back to sufficient supply of oxygen.
- cperciva 4y ago
  Soot is amorphous carbon; that will absolutely be burned at higher temperatures (given sufficient oxygen). You might be thinking of ash, which consists mostly of inorganic residue (although even there you'll see carbonates at low temperatures and metal oxides at higher temperatures). But when we talk about burning wood cleanly we're really talking about smoke -- and that's almost entirely organics (including large amounts of carbon monoxide, methane, and VOCs) which will combust given sufficient heat and oxygen.
- 2000UltraDeluxe 4y ago
  If you have a decent masonry stove, good airflow and dry firewood then most of the particles will simply burn. Once the stove is hot enough, the smoke will ignite and most of that soot is converted into heat and energy.

bcbrown 4y ago

Yes, it can be. By carefully designing the size of the various chambers in a stove, full combustion can be achieved such that the only byproducts are CO2 and H20. This does not happen in a conventional fireplace. Part of the motivating design goals for "rocket stoves" is to achieve this sort of complete combustion. If you're interested in the chemical and physical processes that comprise combustion, I cannot recommend the Faraday Lectures highly enough. Michael Faraday was an experimental physicist, and the data resulting from his experiments were what James Maxwell used to derive Maxwell's Equations for electromagnetic phenomena. Separately, he gave a lecture on candles and combustion, which has been recreated in the original language here: https://www.youtube.com/playlist?list=PL0INsTTU1k2UCpOfRuMDR-wlvWkLan1_r https://www.youtube.com/playlist?list=PL0INsTTU1k2UCpOfRuMDR.... The important intuition is that combustion is a gaseous process. When burning (solid) wood, the heated wood will give off gasses and particulate matter (soot). Those gasses and particulates will combine with gaseous oxygen in an exothermic reaction called combustion. In a conventional fireplace, the oxygen and temperature constraints result in incomplete combustion, leading to particulate pollution as you mention. The search term to learn more about overcoming those hurdles is "rocket stove". In these sorts of stoves, there's a few modifications that result in more-complete combustion. There's separate chambers for the wood and the combustion. In the first chamber, the same processes as in a conventional fireplace occur: the wood burns, creating soot and hydrocarbon gasses. In the second chamber, hot air is added to provide a secondary source of oxygen, and the airflow velocity is reduced (by carefully calculating chamber size using the Bernoulli fluid equation), resulting in complete combustion. By having a right angle between the input from the wood chamber and the chimney, you can achieve a chaotic mixing (in terms of chaos theory) between the wood byproducts and the added oxygen, which also helps ensure complete combustion. So the entire system has the following parts: a chamber to burn the wood; a chamber where hot external air is added and full combustion achieved; a tall chimney to ensure a good draft and airflow; a "bell" to slow air velocity of the hot exhaust and ensure good thermal transfer; a final exhaust port. Here's some resources: https://www.youtube.com/watch?v=IsO9vLn8JHw https://www.youtube.com/watch?v=IsO9vLn8JHw https://en.wikipedia.org/wiki/Rocket_mass_heater https://en.wikipedia.org/wiki/Rocket_mass_heater https://paulwheaton.com/efficient-wood-heat/ https://paulwheaton.com/efficient-wood-heat/ https://permies.com/f/260/rocket-mass-heaters https://permies.com/f/260/rocket-mass-heaters