How much visible smoke? And other concerns from others

We are about to move into a permaculture commuity in Denmark, where we will build our own off-grid tiny house. Our plan is to heat our home with a combination of passive solar and a batch-box or double shoebox RMH which we also want to utilise at the very least for cooking/baking and to some degree as light-source. But now having started the conversation within our community, while some people themselves like the idea and want to use a woodstove for heating, there are also some people against it, being concerned about the pollution as well as the visible smoke. Part of the concern stems from the fact that we are going to build 25 house on a limited space (from what I can see on the map, roughly 1.2 ha) and if everyone would have a woodstove then in the winter the whole air would be filled with "ugly" clouds and the pollution would be at dangerous levels. Another part of that also comes from people with personal experience about woodstoves (not rocket stoves or RMH). Before we started the conversation most people had never heard of rocket stoves or rocket mass heaters and the additional possibility of adding a "smoke washer" (røgvæsker called here in denmark, essentially just passive particulate filter) at the end of the exhaust.

While people do seem to understand that there is a difference in using a rocket mass heater to even a good standard woodstove, it seems some are still having a horror image in their mind of visible fumes coming out on a cold winter day and poising the air, "being responsible for countless of deaths in denmark". I am starting to collect more and more resources on trying to alleviate these fears, showing that burning wood can be done in a safe manner, even if most of us would have one, and on top of that also could be one of the most efficient and sustainable methods to heat our homes with (maybe even the most efficient and sustainable method after passive solar?).

I have quite a few resources already on how RMHs burn more effeciently and heat more effectively due to the included mass and also the possibility of using that same fire for additional functions, thereby making it even more effective. Even here in denmark there are some good resources defending woodstoves, also on how to collect biomass without felling trees (coppicing/pollarding as well as making use of bamboo), etc.

But I am still missing information on some concrete questions that came up and hopefully someone here can help with:
- How long does one generally need to run a RMH for a day in a northern climate for a small house (30-60m2)? 1-2h? And would it be possible to reduce that with passive solar, that on sunny days one might not even need to heat?
- If one burns correctly, how much smoke is there visible over the duration of a whole run? I assume there will be some smoke at the start-up and maybe the end? Are there some videos that could be shown?
- How long is the "start-up" phase of a well-built and well-lit batch-box or dsr RMH? Some people were specifically worried about that phase, knowing it is the most polluting one and arguing that one central stove, distributing the heat to all houses, would be more efficient and reduce the pollution from the start-up phase (which I don't think I agree with, if we also consider line-loss and other possibilities we now loose, like cooking, etc).

Edit: I have also not found resources that go into details about the exact particles that come out of a RMH exhaust and how they compare to other woodstoves (mostly interested here in how dangerous they are for humans), but given that there are RMH here in the EU that have been certified and are far surpassing the current 2020 regulation as well as the upcoming 2022 regulation, I hope that this will provide enough security for people on that front.

I would say before you bother with all that find out how to connect one to a standard chimney, you have to have it swept and inspected either once or twice a year (it's twice in my present house, was once in the previous) that is a legal requirement and cannot be avoided once bbr has the heating type down. he even has to inspect the second chimney that is not in use and hasn't been for several years.

There's a few threads lying around here on RMH heater smoke and as far as I can see nothing has been actually checked on particle size.
You could try the money angle as well, a central pellet furnace will cost a fortune to run (but produce no visible smoke), straw while it is cheap requires a tractor and really smokes a lot. ground heat would work but is expensive to install and it appears it has a limited lifespan, air/air heatpumps are probably the most obvious solution.

If you figure out how to get one properly allowed can you make a thread on how to do it? it could be very useful for others.

Interesting community issue.
I have witnessed the effect of 'dirty' wood fired heaters and the consequent smell etc.
Something always denied by the perpetrator.

The output of a decent RMH will be clear. There may be some heat shimmers or a small cloud of water vapor condensing that dissipates in less than ten feet, depending on atmospheric conditions. With good, dry wood mine puts out a burning wood campfire smell for less than ten minutes at worst. At temperature, there is a pleasant smell of cleanly gassified wood/charcoal burning.

Skandi Rogers wrote:I would say before you bother with all that find out how to connect one to a standard chimney, you have to have it swept and inspected either once or twice a year (it's twice in my present house, was once in the previous) that is a legal requirement and cannot be avoided once bbr has the heating type down. he even has to inspect the second chimney that is not in use and hasn't been for several years.

There's a few threads lying around here on RMH heater smoke and as far as I can see nothing has been actually checked on particle size.
You could try the money angle as well, a central pellet furnace will cost a fortune to run (but produce no visible smoke), straw while it is cheap requires a tractor and really smokes a lot. ground heat would work but is expensive to install and it appears it has a limited lifespan, air/air heatpumps are probably the most obvious solution.

If you figure out how to get one properly allowed can you make a thread on how to do it? it could be very useful for others.

Hmm, good to know about the chimney inspection, I should have already guessed that it can not be that easy to be off-grid here in denmark and be independent of costly services (and the monetary economy) for most things.

But what do you mean, if I figure out how to get one properly? I know at least two people here in denmark who have a rocket mass heater installed, I have not talked to them about details, but I assumed that it was not that difficult.

I know of two danish comapnies selling RMHs: https://fornyetenergi.dk/ and https://oekobyg.dk/

I think the central pellet furnace is not really anything the majority is interested in, I think it was more for the sake of argument. Yeah, ground heat and air/air heatpumps both have come up and I assume some people will probably go for the latter (if there are not a group of people who will get ground heat together) - but my aim is really to have an as much as possible electricity free house (certainly for all basic appliances like heating), in fact the plan is to not even have electric wiring installed. But yeah will be interesting where we will get to over the coming months. We are already in talks with the "kommune" (district) about some of these topics (off grid in general, but I don't think heating so far) and up until now they have responded positive to our ideas.

Markus Padourek wrote: - How long does one generally need to run a RMH for a day in a northern climate for a small house (30-60m2)? 1-2h? And would it be possible to reduce that with passive solar, that on sunny days one might not even need to heat?

It greatly depends on the level of insulation, but in our passive house in the Netherlands we use a 150 mm batchrocket system with a weight of two metric tons. Our house is larger, but the heater is run one charge of 3 to 6 kg soft wood species in the evening while it isn't freezing. The load is tailored to the weather forecast, more sun during the day means a smaller load. During frost periods we run it twice a day, during breakfast and diner. We had a cold spell in February with lots of sun during the day, one evening charge being enough. I have to admit the house sports a lot of glazing facing south, this helps a lot!

Markus Padourek wrote: - If one burns correctly, how much smoke is there visible over the duration of a whole run? I assume there will be some smoke at the start-up and maybe the end? Are there some videos that could be shown?

In a mass heater the core won't cool down completely between burns. We emploi the top-down lighting method, which emits a very little bit of smoke for about 5 minutes during startup. There's lots of water vapor visible during most of the burn of course, exit temperature at the top of the chimney is estimated between 80 and 100 ºC most of the time. This vapor plume dissolves in the air within a couple of meters and is transparent most of the time. It's appearance is much alike the vapor from a condensing natural gas boiler.
No smoke at all at the end of the burn, definitely.
There's a very old video, illustrating what is visable in frosty weather. At the time I could stand there, my head in the plume and frantically sniffing, only to detect a very faint smell of wet charcoal. Mind you, it happened to be a large fire that was raging in my workshop at the time.

Markus Padourek wrote: - How long is the "start-up" phase of a well-built and well-lit batch-box or dsr RMH? Some people were specifically worried about that phase, knowing it is the most polluting one and arguing that one central stove, distributing the heat to all houses, would be more efficient and reduce the pollution from the start-up phase (which I don't think I agree with, if we also consider line-loss and other possibilities we now loose, like cooking, etc).

Starting up time of a warm-but-not-hot batch box rocket is about 5 minutes, 10 minutes tops.

Markus Padourek wrote:Edit: I have also not found resources that go into details about the exact particles that come out of a RMH exhaust and how they compare to other woodstoves (mostly interested here in how dangerous they are for humans), but given that there are RMH here in the EU that have been certified and are far surpassing the current 2020 regulation as well as the upcoming 2022 regulation, I hope that this will provide enough security for people on that front.

Personally, I've seen the results of two tested batchrockets. First and foremost, those things emits very little smoke to begin with, the dangerous particles are organic, i.e. soot. The particles that remain are anorganic, the residue that can't be burned because these are the minerals that are taken up from the soil by the trees. The limit of dust concentration in the 2022 EU rules is 40 mg/m³ if I remember correctly, both the two rockets did 20 mg/m³. Both were bell constructions, which means gas velocity nearly stalls while entering the bell, so most of the dust is settling at the floor of the bell. The first time I checked my heater I stuck my hand through the cleaning hatch and I couldn't feel a thing. I tried again and waved a bit with my fingers, there was some resistance then. Very fine dust, not what one would call ashes from wood burning.

Suffice to say, batchrocket don't sport an ash drawer because there's no need to, anorganic ash particles are a very very small percentage of the wood's makeup.
I hope this helps.

Those two sites talk about masonry stoves which are indeed common and I doubt that type would be any issue to get certified. I just remember a discussion here that was talking about issues connecting a rocket to a normal chimney, which would then cause an issue here. The solid residue printed on the bags of pellets varies between 3% and 4.5% ish. we notice a change in the ash if anything is slightly off with the furnace. wiki states somewhere between 0.5 and 1.4% as being unburned at over 750C (1380F)

Skandi Rogers wrote:Those two sites talk about masonry stoves which are indeed common and I doubt that type would be any issue to get certified. I just remember a discussion here that was talking about issues connecting a rocket to a normal chimney, which would then cause an issue here. The solid residue printed on the bags of pellets varies between 3% and 4.5% ish. we notice a change in the ash if anything is slightly off with the furnace. wiki states somewhere between 0.5 and 1.4% as being unburned at over 750C (1380F)

Yes, I guess they can build it within the masonry stoves rules, which I have heard is also the case for some states in the US, but they do talk specifically about rocket stoves on their pages: https://fornyetenergi.dk/raketovne/ and http://oekobyg.dk/?page_id=60

But yeah, I don't know that much about these details yet, my plan was to get help from one of these two companies to figure out how it best makes sense to build one in our house.

Peter van den Berg wrote:

Markus Padourek wrote: - How long does one generally need to run a RMH for a day in a northern climate for a small house (30-60m2)? 1-2h? And would it be possible to reduce that with passive solar, that on sunny days one might not even need to heat?

It greatly depends on the level of insulation, but in our passive house in the Netherlands we use a 150 mm batchrocket system with a weight of two metric tons. Our house is larger, but the heater is run one charge of 3 to 6 kg soft wood species in the evening while it isn't freezing. The load is tailored to the weather forecast, more sun during the day means a smaller load. During frost periods we run it twice a day, during breakfast and diner. We had a cold spell in February with lots of sun during the day, one evening charge being enough. I have to admit the house sports a lot of glazing facing south, this helps a lot!

Markus Padourek wrote: - If one burns correctly, how much smoke is there visible over the duration of a whole run? I assume there will be some smoke at the start-up and maybe the end? Are there some videos that could be shown?

In a mass heater the core won't cool down completely between burns. We emploi the top-down lighting method, which emits a very little bit of smoke for about 5 minutes during startup. There's lots of water vapor visible during most of the burn of course, exit temperature at the top of the chimney is estimated between 80 and 100 ºC most of the time. This vapor plume dissolves in the air within a couple of meters and is transparent most of the time. It's appearance is much alike the vapor from a condensing natural gas boiler.
No smoke at all at the end of the burn, definitely.
There's a very old video, illustrating what is visable in frosty weather. At the time I could stand there, my head in the plume and frantically sniffing, only to detect a very faint smell of wet charcoal. Mind you, it happened to be a large fire that was raging in my workshop at the time.

Markus Padourek wrote: - How long is the "start-up" phase of a well-built and well-lit batch-box or dsr RMH? Some people were specifically worried about that phase, knowing it is the most polluting one and arguing that one central stove, distributing the heat to all houses, would be more efficient and reduce the pollution from the start-up phase (which I don't think I agree with, if we also consider line-loss and other possibilities we now loose, like cooking, etc).

Starting up time of a warm-but-not-hot batch box rocket is about 5 minutes, 10 minutes tops.

Markus Padourek wrote:Edit: I have also not found resources that go into details about the exact particles that come out of a RMH exhaust and how they compare to other woodstoves (mostly interested here in how dangerous they are for humans), but given that there are RMH here in the EU that have been certified and are far surpassing the current 2020 regulation as well as the upcoming 2022 regulation, I hope that this will provide enough security for people on that front.

Personally, I've seen the results of two tested batchrockets. First and foremost, those things emits very little smoke to begin with, the dangerous particles are organic, i.e. soot. The particles that remain are anorganic, the residue that can't be burned because these are the minerals that are taken up from the soil by the trees. The limit of dust concentration in the 2022 EU rules is 40 mg/m³ if I remember correctly, both the two rockets did 20 mg/m³. Both were bell constructions, which means gas velocity nearly stalls while entering the bell, so most of the dust is settling at the floor of the bell. The first time I checked my heater I stuck my hand through the cleaning hatch and I couldn't feel a thing. I tried again and waved a bit with my fingers, there was some resistance then. Very fine dust, not what one would call ashes from wood burning.

Suffice to say, batchrocket don't sport an ash drawer because there's no need to, anorganic ash particles are a very very small percentage of the wood's makeup.
I hope this helps.

Thanks for the information Peter, that does indeed help a lot. The idea would be to have well-insulated houses, and at list for our house designed with passiv solar principle, but not to passive house standards. And how long is each run for you on average?

I did not know there was a difference between smoke and vapor plume (I am still relatively new to this topic) - what exactly is vapor plume? Is this purely because the hot air meets with the cold air? And apart from the different smell this is clear visually because it is purley white fumes, rather than the typical dark ones, right?

Also I would be curios, which batchrockets results do you know of? I only know of https://www.uzume.fr/

Markus Padourek wrote:

But yeah, I don't know that much about these details yet, my plan was to get help from one of these two companies to figure out how it best makes sense to build one in our house.

Yes it looks like you will have to get a company in to do the entire thing, as the stove has to be tested and one can't take a rocket mass heater to a testing center! Actually the more I look into it the worse it gets, it varies by council as well good grief they like to make things complicated. I think a quick ring to them and see if it's possible in your kommune the company can probably answer that pretty easily. reading around you even need a license to put one in a greenhouse!

Ovnen – eller typen – skal være afprøvet på et godkendt afprøvningsinstitut. Den må højest udlede 4g partikler pr. kg træ, der fyres med.Prøvningsattesten skal følge med brændeovnen ved salg. Når brændeovnen tilsluttes, skal skorstensfejeren underskrive prøvningsattesten, som ejeren skal gemme som dokumentation. En brugt brændeovn må ikke sælges eller installeres uden prøvningsattest. Måske kan forhandleren, hvor den er købt, skaffe en, hvis typen siden er godkendt.

(stove (or type) must be tested at a certified test center and may only produce 4g of particles per kg wood, (a bit about keeping the documentation with the stove) a used stove may not be sold or installed without the test. Maybe the seller can get it if the type of stove is certificated)

here's the full horror story, but how to apply it I think you'll need their help with
https://www.retsinformation.dk/eli/lta/2020/541

Markus Padourek wrote:Thanks for the information Peter, that does indeed help a lot. The idea would be to have well-insulated houses, and at list for our house designed with passiv solar principle, but not to passive house standards. And how long is each run for you on average?

Duration of a single run is something between 45 minutes and 1 hour, depending on fuel species.

Markus Padourek wrote:I did not know there was a difference between smoke and vapor plume (I am still relatively new to this topic) - what exactly is vapor plume?

Vapor is moist air, lots of water in the exhaust gases. On a chemical level, result of complete combustion is heat, CO² and water. One kilogram of absolutely dry wood will produce 0.5 liter of water. In the exhaust gases this water is in gaseous form so it won't condensate in the chimney as long as the exhaust temperature is above 45 ºC.

Markus Padourek wrote:Is this purely because the hot air meets with the cold air?

Yes, the steam condensates in the cold air as droplets which immediately spreads out and makes clouds of visible "steam" (*fog*) until it spreads out enough to evaporate again. Often the visable plume begins some distance above the chimney exit, 30 cm (1 ft) is no exception.

Markus Padourek wrote:And apart from the different smell this is clear visually because it is purley white fumes, rather than the typical dark ones, right?

Yes, the smell of wet charcoal is from 9-methyl ketone in very small quantities, real complete combustion is very, very close then. Real smoke moves much slower and tend to drift away without disappearing.

Markus Padourek wrote:Also I would be curios, which batchrockets results do you know of? I only know of https://www.uzume.fr/

There's one Dutch guy who used the technology to build his own heater but refuses to recognize my work. He had his heater tested, one page of the report is here:



Another guy, from Belgium this time, implemented his own heater much later, his result page is here:

Peter van den Berg wrote:

Markus Padourek wrote:Thanks for the information Peter, that does indeed help a lot. The idea would be to have well-insulated houses, and at list for our house designed with passiv solar principle, but not to passive house standards. And how long is each run for you on average?

Duration of a single run is something between 45 minutes and 1 hour, depending on fuel species.

Markus Padourek wrote:I did not know there was a difference between smoke and vapor plume (I am still relatively new to this topic) - what exactly is vapor plume?

Vapor is moist air, lots of water in the exhaust gases. On a chemical level, result of complete combustion is heat, CO² and water. One kilogram of absolutely dry wood will produce 0.5 liter of water. In the exhaust gases this water is in gaseous form so it won't condensate in the chimney as long as the exhaust temperature is above 45 ºC.

Markus Padourek wrote:Is this purely because the hot air meets with the cold air?

Yes, the steam condensates in the cold air as droplets which immediately spreads out and makes clouds of visible "steam" (*fog*) until it spreads out enough to evaporate again. Often the visable plume begins some distance above the chimney exit, 30 cm (1 ft) is no exception.

Markus Padourek wrote:And apart from the different smell this is clear visually because it is purley white fumes, rather than the typical dark ones, right?

Yes, the smell of wet charcoal is from 9-methyl ketone in very small quantities, real complete combustion is very, very close then. Real smoke moves much slower and tend to drift away without disappearing.

Markus Padourek wrote:Also I would be curios, which batchrockets results do you know of? I only know of https://www.uzume.fr/

There's one Dutch guy who used the technology to build his own heater but refuses to recognize my work. He had his heater tested, one page of the report is here:



Another guy, from Belgium this time, implemented his own heater much later, his result page is here:

Thank you for that detailed information, I also just had a look at yocoon (https://www.yocoon.com/hoog-rendement/) and this will be super-useful data to show. Especially this paragraph:

"In addition to the quantity in an absolute sense, the composition and toxicity of the emitted dust also differs. With good combustion, the dust emission can be limited to approximately 20-50 mg / m3. The composition of the emitted dust then mainly consists of the inorganic components present in the biomass (salts), the toxicity of which is not significant. In contrast, poor combustion not only drastically increases the amount of dust, but also the content of organic condensable tars and soot. These are often toxic or carcinogenic components, which are of great importance for public health"

Which comes from a report linked from a government agency from the netherlands.

Great, so I can show, that as long as properly dry biomass is used and the fire is started correctly, there will be only very little smoke for about 5 minutes and then for the rest of the burn there will be no smoke, just vapor plume (i.e. steam) and the resulting particle emission has an insignificant impact on our health.

Interesting, I just found https://www.blauer-engel.de/en/products/construction-heating/stoves-for-wood - a voluntary german label where particle concentration has to be max 15mg/m3 and additional a particle count  concentration of 5.000.000/cm³ can not be exceeded. It seems currently certified models achieve this by making use of a filter. I wonder if RMHs could be designed to achieve this level without a filter, but I also wonder, given the writing from the dutch agency and some dansih and swedish studies I read about, if there would even be any health benefits of achieving a particle concentration of 15mg/m3 rather than 20mg/m3.

I have no official information, but I am happy to share my personal experience.

Markus Padourek wrote: - How long does one generally need to run a RMH for a day in a northern climate for a small house (30-60m2)? 1-2h? And would it be possible to reduce that with passive solar, that on sunny days one might not even need to heat?

I have a very large house (340 m2), poorly insulated (R10 or less overall, two story, RMH in the first floor). I don't live in a northern climate.  I use a small amount of passive solar which is concentrated in winter months and the late afternoon. I need to fire my 8" RMH around three hours each morning. More or less depending on weather. We like to sleep cool, so we don't fire in the evening usually.

Markus Padourek wrote: - If one burns correctly, how much smoke is there visible over the duration of a whole run? I assume there will be some smoke at the start-up and maybe the end? Are there some videos that could be shown?

For my machine, there is very little smoke. Unless you're looking for the heat shimmer, most of the time you will see nothing. No lengthy plume of smoke. On start up is be a large plume of water vapor depending on temperature, but this will evaporate quickly, again depending on temperature and humidity. There is likely some smoke in there at first, but it dissipates among the water vapor. After warmup, only heat shimmer. Sometimes there is thin diffuse whitish smoke during the burn with shifting wood and temperatures but compared to the old iron stove I grew up with, you might not even notice. It is very light, and dissipates before leaving the footprint of the house. There is occasional burning wood smell, but pleasant and not obtrusive. Overall, unless you're really paying attention, most people will probably not even notice the stove is operating.

Markus Padourek wrote: - How long is the "start-up" phase of a well-built and well-lit batch-box or dsr RMH? Some people were specifically worried about that phase, knowing it is the most polluting one and arguing that one central stove, distributing the heat to all houses, would be more efficient and reduce the pollution from the start-up phase (which I don't think I agree with, if we also consider line-loss and other possibilities we now loose, like cooking, etc)..

My stove has a ceramic fiber core so warmup is pretty short. 5-10 minutes. However, it is a J-tube. The primary key for a fast warm up is to stick with fine kindling with high surface area that lights quickly. I also use a torch to light, so no smoky paper.

I would say in many cases, especially in cities, central heating systems would be a better solution. But rocket mass heaters are so efficient at point of use, that I would think the overall efficiency is better with a home heating unit. You also have cooking and radiant heat, as well as the ability to burn paper waste (once hot, also it makes a lot of ash) as well as yard waste, sticks, wood waste, construction debris if you can find it, etc. You can't really do these things with a neighborhood scale unit.

If I harvest a tree, I use all of the tree except the stump and roots. I chip the small branches and leaves/needles (for composting toilet substrate) and anything too large for the chipper is firewood. With commercial scale operations, anything involving wood is hugely wasteful. They estimate for lumber, around half the total wood makes it into construction.

Anyway, I hope some of this is helpful.

Markus Padourek wrote:Interesting, I just found https://www.blauer-engel.de/en/products/construction-heating/stoves-for-wood - a voluntary german label where particle concentration has to be max 15mg/m3 and additional a particle count  concentration of 5.000.000/cm³ can not be exceeded. It seems currently certified models achieve this by making use of a filter. I wonder if RMHs could be designed to achieve this level without a filter, but I also wonder, given the writing from the dutch agency and some dansih and swedish studies I read about, if there would even be any health benefits of achieving a particle concentration of 15mg/m3 rather than 20mg/m3.

This is a very interesting question. I wonder with my stove, with a split barrel bench, with a huge surface area inside and much area for particle settling, would have a low particle output.

I remember with the cast iron stove I grew up with, there were always ashes and sparks coming out the chimney.  In mine, about half the ash stays in the firebox, a quarter in the bottom of the manifold, and another quarter in the first half of the bench. The last half of the bench has virtually nothing, only some soot precipatates on edges of things.