carbon monoxide: natural gas vs. wood stove vs. rocket mass heater

I've seen this question come up about nine times in the last two months.  

Here is what I know for sure:

  - anything that burns generates carbon monoxide

  - one tenth the burning leads to one tenth the CO

  - peter tested a rocket mass heater and showed it burning cleaner than natural gas or conventional wood stoves:



  - matt walker had similar results:






I would like to be able to say that running a rocket mass heater typically generates less than 3% of the carbon monoxide than a natural gas heater.  But to get there, the first step is to get an understanding of how much CO does a natural gas heater put out.  And then I would like to get an understanding of how much CO does a conventional wood stove put out?  

My impression is that natural gas heaters need to be adjusted so that the CO in their exhaust is kept low.  Without that, the CO could be huge.



I know that for CO2, heating a home with a standard wood stove puts out about a tenth of the CO2 that a home heated with natural gas puts out.  So there is the potential that it could be similar for CO.


I tried to find information on overall CO emissions for natural gas heat, but ....  my google-ju must be off today.

I think another important point to add in here, is that sometimes somebody freaks out about CO and rocket mass heaters.  This has universally been the issue of confusing "rocket stove" with "rocket mass heater".  A rocket stove is something that is typically not vented to the outside (usually used a bit like a camp stove for outdoor cooking).  A rocket mass heater is always vented to the outside.  

Correct me if I'm wrong here but I've thought that CO2 was a greenhouse gas issue and CO was a safety issue if it's released inside the house.  Assuming that's correct, is the CO that Peter measured at the exhaust or is it inside the residence?

True.

The reason I am asking is that there seems to be fud about rmh and co.  I would like to be able to say that when it comes to co, rmh is much safer than natural gas or conventional wood stoves.

Anything that burns is going to generate CO, sure, but with excess O2, that'll drop off real quickly as the CO burns and forms CO2. 14% would be a lot extra for a natural gas furnace (designed that way so you're not heating up extra air that's going to be exhausted out the stack). Since a RMH cools the exhaust so much, the loss in efficiency from that isn't an issue.


Would be interested in PPM NOX. NOX generally increases with excess air until you add so much you cool the flame temperature, and is generally something heater manufacturers are more worried about than CO. If everything I've seen about RMH is to be believed, you get more than hot enough in the combustion chamber to form NOX. Not knocking RMH by any means, just curious...

I believe the very hottest experimental RMHs can get to nitrogen burning temperatures, but probably any version out in the field won't get that hot. I don't think there is anything (useful) beside nitrogen that is still unburned at those kind of temperatures, so there is no reason to go for the extreme anyway.

Thanks for these numbers.  Can someone please translate to layperson's English what the abbreviations stand for in the meter read-out? what would be the normal comparison for burning natural gas, coal?  Thanks.

I think this is also a good time to point out that nobody has ever gotten sick from storing wood.  Entire houses are made of wood and "leak" constantly, but it would seem that that is not a problem.  

However, if you have a natural gas leak, that can be very serious.  

Trying to get a truthful and accurate conclusion in conversation with New Scientist still. Even meeting and exceeding stringent German emissions limits for particulate for a wood stove is still as bad as driving many bad trucks.  sO--what about sticking a dust mask over your chimney?? Exhaust temperature is way way way below combustion temp for paper 451 Fahrenheit) at about 160 Fahrenheit yes? Im assuming the material is in the ballpark of paper.


Has anyone done this? Any safety issue im missing?  Cost is low--a dust mask is .20 USD from casual web search.  How many burns would one dust mask paper handle?


Thanks!!!

OK, talked with Ernie, the filtering idea seems a) unnecessary and b) impossible.  It woudl require forced air, and the burn that creates emissions is lasting 5" to 15" out of the day cycle.  This may seem obvious to most of you, but when I'm looking at how the legal testing is done, it creates a lot of confusion (one site says the masonry heater passed the emissions test with 1/4 of the legal limit, whereas I would expect it to be far, far lower, if the test is run for a full 24 hours--and it sounds like it simply isn't run that way).

The next question I have is, is anything still burning inside the RMH after the intial burn?  if not, can you simply _close your chimney entirely_? might that not help dispel arguments that the emissions are anything like a constantly smoldering regular/eco-label woodstove?

I'm looking for talking points here, not so much practical strategies.  Thanks!

Once the fire is out, it's out, except for any lingering coals, with no particulates being generated. The coals are still generating some CO2 until they are dead. Any other particulates would come from a draft stirring up the ashes, and if you have sealed the intake with a couple of bricks there will be not enough draft to make eddies and currents.

This is all my speculation, of course, as I have no way to actually measure the output from the chimney, but I think it is reasonable.

I think there is a lot of confusion because we are talking about lots of different things at the same time . They may sound similar but they are not .
Equating the combustion of natural gas - methane with the combustion of what is in effect solid carbon - wood coal etc I do not think should  be regarded as the same .
If you look at what is going on with carbon it's either
C + O2 ~ CO2
2C + O2 ~ 2CO
Thus the effect of an over supply of oxygen will favour the first also promoting the further possibility
2CO + O2 ~ 2 CO2

With methane things are much more complex
CH4 + 2O2 ~ 2H2O + CO2
CH4 + O2.  ~ 2 H2O + C (soot )

The soot then burns as per the coal above in a further reaction . I don't know if folks remember the old lessons with a Bunsen burner and the yellow flame and the blue flame that what we are talking about .
As for nitrogen burning I would not worry as apart from special circumstances such as lightning strikes of enclosed car engines the likelyhood of a reaction is extremely low in a normal fire or even a rocket mass burner . If you manage to do it I suspect Dow or ICI would like to know how and your fortune is made .

David

This was recorded at the 2017 Rocket Mass Heater Workshop Jamboree.   Me, Erica, Donky, Mud and Peter take a stab at carbon monoxide stuff while Ernie just looks pretty.

Mike Jay wrote:Correct me if I'm wrong here but I've thought that CO2 was a greenhouse gas issue and CO was a safety issue if it's released inside the house.  Assuming that's correct, is the CO that Peter measured at the exhaust or is it inside the residence?

Don't fool yourself. CO2 can be posionious  too. Concentrations have to be much higher on a ppm basis. If I remember correctly CO will chemically bind in the blood while CO2 is an absorption issue.

As the last panelist in the video opined it is good insurance to have a CO detector. Its reasonably cheap insurance against an accident.

In my house anyway, of the wood burning stove, the wood/coal boiler, and my propane boiler; the propane boiler is the safest of the three in terms of carbon monoxide.

That is because for safety sake it takes in air from the outside of my house, heats it, then returns it out through the exhaust stack. Because it is a closed loop that does not use air inside my home, it is simply the safest for me and my family. If drafting problems, or components in the appliance fail, the computer instantly shuts down the appliance.

Of the other two stoves, the wood/coal boiler is the next safest because it has a variable speed forced draft eliminating drafting issues on damp, low pressure days, or windy days and like the propane boiler, draws air from outside my home.

My non-EPA compliant 1893 wood burning stove is the least safest only because drafting in that heating appliance can be tricky. I live on a hill so wind is more of an issue then damp low pressure days, but as I type this my eyes are watery from smoke as we just went from a VERY windy day yesterday to dead calm now. I was forced to use the damper to keep the high wind from down drafting the chimney and chuffing smoke into the house yesterday. I woke up with it closed and not drafting up the chimney this morning, so it shows it is very temperamental. Also, unlike my other two heating appliances, it draws air from INSIDE my home.

...

In terms of fuel safety which is another issue entirely, there is no question that a house full of wood does not explode. Here in Maine we do not have much natural gas as it is Propane making it a bit safer as elements are added to make it smell in case of a leak. In 23 years of having back up propane however I have never had a leak. Within propane there are two sides; the liquid side, and then the gas side, and of the two the liquid side is much safer. Should a leak develop, the propane is so cold that it instantly freezes when it hits atmosphere. Then it thaws. Then it freezes. Then it thaws, and so it goes until the product is dispensed. 99% of the time a liquid propane leak for first reponders is to just wait until the problem resolves itself. On the gas side, it is a little more volatile, but people have a unhealthy fear of it when they really shouldn't. My father was an appliance repair man for years and would often check for leaks with a lighter. A leak would blow the flame of his lighter out...not blow up. There is only 11 inches of pressure at an appliance, and the volume of propane to air is so low that combustion is impossible. Now a room pumped full of propane...yes that would blow up, but is very rare, modern regulators are designed to prevent that very thing from happening. Now I have heard of (2) houses in Maine exploding from propane explosions in the last 10 years, yet on my hill alone, of 5 houses, mine has been the only one that has not had a major fire from a wood stove. Three have burned completely to the ground, including my parents.

As for coal, coal explosions can and do happen, and I have experienced one in 23 years of burning the black rock. For the record this has always been Anthracite coal and not Bituminous or Lignite coal which have a bit more coal gas within it than Anthracite.  In my case the explosion happened because of my own stupidity. I was burning coal merrily away and wanted to try a coal/pellet mix to see if I could get extended burn times. When I shoveled in a few pounds of pellets over the burning coal bed, I did not have time to mix the material before the coal gas coming off the coal bed built up, but with ample heat inside the stove, it blew up. It was not huge, and my stove pipe riveted together easily handled the fireball going up the chimney, but I experienced it. But it was 100% my stupidity that caused it and not from normal coal burning.

Safety wise, coal is MUCH safer than wood only because there is no creosote with coal so it is impossible to have a chimney fire. Equally, once the coal is bed is burning, it will slowly begin to dwindle as it begins to plug with ash. This is in contrast to wood that can smoulder for awhile in a wood stove, then suddenly roar to life once certain burn conditions are met. In other words I can leave my home with a coal fire going knowing it will never suddenly roar to life an hour after I am gone. It will only burn in proportion to the amount of air and coal I give it; very predictable.

...

In short propane, natural gas and coal are "safer" only because they are more consistent in content. Because of that, human controls to move and consume the products have been developed over many years of development. However I am not at all advocating for them. With consistency and control over the product, comes control over the product line, and living in Maine I spend too much money to heat my house every year no matter what with, to be held hostage by high prices to any one heating product. Propane is safe and easy, but also expensive. Coal is cheaper, but still comes from a supplier. Wood comes from my own land, but is less safe. Still, for me and my family, I am going to mitigate those safety concerns as best I can, run with scissors like I did in kindergarten, and do the best I can to provide for myself by heating with wood for the majority of my heating needs.

I do not have a Rocket Mass heater so I cannot state experience on them, however they burn wood. Wood is an inconsistent product so it has a lot of unknowns, but I would not say they are inherently dangerous either. Mitigate potential problems and move on without fear...

I just thought of a rather unusual point to add to this discussion.
While I agree that you can't mess around with CO gasses in your home, I don't see what the concern is over the RMH system. Clearly. if you have watched it in action, you can see that any gasses that are being created are being sucked up through the stack. People raise such an alarm over CO poisoning with good reason, but I bet that sitting in your car to let it warm up could give you a higher dose of CO gas than the RMH. When properly installed, I don't really see any concern with the RMH versus other heating sources. We breathe CO every time we step outside near traffic, warm up our cars, or enter a subway.
I personally have a natural gas heater in my home, and the thing malfunctioned one year and filled my home with CO gas. These systems are considered the "standard" and supposed to be safe. My point here is that Mud was right, you should always have a CO monitor if you are concerned about that issue. Any heater can cause this kind of poisoning, so why is no one raising a concerns over their "standard" heaters?
Keep on burning with the RMH!!! And leave the rest to God!

Travis - I have known quite a few folks who had a coal fire and the chimney caught fire it used to be quite common in the UK

David

David Livingston wrote:Travis - I have known quite a few folks who had a coal fire and the chimney caught fire it used to be quite common in the UK

David

That is because the coal in Europe is quite inferior to the coal we have in the United States. The coal we use for heating is known as hard coal, also called Anthracite Coal. Very few places in the world have anthricite coal, and here in the USA it is found in the Northeast part of Pennsylvania and burns incredibly hot and does not produce creosote. With it, it is impossible to have a chimney fire. There are numerous locations here in the US with bituminous coal, but even that is superior to what Europe has which has brown coal or lignite, which lower in quality still.

Sometimes I forget that Permies is quite diverse internationally and should have put a anthracite coal disclaimer on my post. Thanks for keeping me straight.

We do have anthracite over here in Wales which is certainly not inferior to what you have in the United States. It burns very hot with virtually no visible smoke.

We ourselves only burn wood - safely...

I'm being a bad girl and not reading this entire discussion thoroughly. I just wanted to throw in a few Googles I had done in trying to figure out certain system hazards that I didn't see touched on in my un-thorough speed reading of the discussion.

On carbon monoxide and combustion: https://www.abe.iastate.edu/extension-and-outreach/carbon-monoxide-poisoning-checking-for-complete-combustion-aen-175/

On carbon nuetrality:
http://articles.extension.org/pages/43727/is-burning-wood-carbon-neutral

So, link 1, point 1: wood stoves is a bit how they are managed is related to efficiency.

Link 2, point 2, again: management. If you manage your word resources for renewability, then CO2 created is negated, but if you manage unrenewably, which fossil fuels are by definition, you are adding GHGs.

I hope this adds value to the discussion.

John Harrison wrote:We do have anthracite over here in Wales which is certainly not inferior to what you have in the United States. It burns very hot with virtually no visible smoke.

We ourselves only burn wood - safely...

Oh yeah, no smoke at all, and gobs of heat which is why I love it, not to mention incredible long burn times. I was once burn anthracite coal and it was really cold, maybe -20 (f) when my Grandmother across the street asked why I was not burning coal, and I said I was: she could not tell because only a haze was coming off the chimney.

Coal here is making a big comeback. Pellets are dying off as they have not lived up to the hype and promises given. Myself I shuttle between coal and wood a lot, but I have a pot bellied stove so I can do that. It depends on how cold it is. Yesterday was 13 (f) outside so I was burning coal, but today it is 32 (f) so I am burning wood.

Sometimes I am not very clear on what I say, and I think this was a huge case in point. I think the reality is it takes very little carbon monoxide to kill people in residence when the conditions are right. I know of a family of 6 squatters that broke into a mobile home of a family friend, were using a kerosene heater to drive off the cold, and ended up all perishing from carbon monoxide poisoning. That is sad...

So with that being said, to me it is not how much each appliance produces of carbon monoxide, (they all produce it, they all have the potential to kill), it is how many times atmospheric conditions can change to allow that lethal gas to enter a home. In my house, of a propane boiler, a wood/coal boiler, and a wood burning stove...the latter sadly down drafts due to low pressure weather systems, wind, damper settings, etc. So even if my propane boiler did produce more carbon monoxide, because it takes in air from the outside, then expels it back outside it is impossible for it to emit carbon monoxide into my home.

I think in this case people take affront to that because rocket mass heaters and wood stoves play a prominent part in energy independence, and without question a wood burning stove or rocket mass heater is one of the most cost effective appliances to install in a home, look beautiful, and save on energy, but we are not doing ourselves any favors by mitigating a reality either, and that is; downdrafting can be a problem. Sure on a clear, cold day my woodstove drafts perfectly, but what about on a dreary, foggy day when the house is just chilled enough that I want a warming type of fire? Those are atmospheric conditions prone to downdrafting. When constructing these stoves, (even wood burning stoves) we MUST be super diligent in ensuring proper draft.

One result of having less fires is what to do with the firemen ?
I think we also need to be clear when talking about saftey is the differnce between a lot of CO for a short while and a little CO for a long time both can kill but the latter is more difficult to notice .

David

So to address down-drafts in atleast RMH and wood burners. There's ways to plumb the high efficiency wood burners and I'm sure this can go for batch-box RMHs, to pull air from the outside. So although the heat is inside, the airflow is all outside. You then have to just worry about your house being holey and drafts coming back that way. This is supposedly a more efficient way to heat anyway, since then your not sucking cold air in to your house to heat it. If you plumb it like that, then your carbon monoxide problems are virtually nil. You'd have to have a crack somewhere in the pipes or an open window on a strong down-draft day near the intake vent. Even then, you can be extra careful and build hot fires and let the thermal mass be your long-term heat storage. In fact, I think that's kinda how the RMHs are supposed to function, and I theorize the new high efficiency wood burning stoves can do this quite well too. I'm attaching sketches of how mine is both designed and plumbed for comparison to RMH design. Not exactly the same, but close. I have a few more efficiency upgrades I want to do to it and a boat load more for the house to get the sucking-insulating balance right and improve our use of thermal mass.

P.S. You know a topics's good when you wake up thinking about it.

P.P.S.: Sorry the images are so poor quality. Some day I might upgrade to a decent camera phone. In the mean time, I'll explain what your seeing: That's brick surrounding the burner. The burner itself has no direct heat escape (insulation covers most of the top of the chamber) and rests on the cold air input, creating a circulation within the chamber that means you can put your hand above the un-plumbed unit without it burning most of the time. Any heat that does escape up has about 25' of stainless steel plumbing in a brick chimney before it leaves the house. The rest of the heat either stays in the burner which has some thermal mass via fire brick, or dissipates to the surrounding cast iron box and adjacent fire brick, regular old brick, or tile, or comes off the unit as air heat for the room, via the fan.

One more thing to address the CO dangers: old homes, which were designed rather breezy, that then get insulated to stop air movement, and then have a fire lit in an old (sometimes leaky) fire place, which worked fine when the fire didn't have much trouble pulling air through the house is now more prone to back drafting and leaking. Which, would be a problem, but not a huge problem, if the house was still really air leaky. But, with good insulation, CO, which is a light gas and should wander up and away, gets stuck inside in larger quantities than it would have otherwise. Additionally, this well insulated house might not get as cold and therefore not "need" as big of a fire. So the type of fire lit might be one that has incomplete combustion, making it produce a greater quantity of CO. This is my theory as to where you have your biggest CO dangers in homes these days (besides malfunctioning equipment). For these homes the right thing might actually be to always plumb to the outside, especially if, as in most cases, the residents don't understand fire science. This is probably why it is recommended you crack a window when burning a fire, which I assume would not be necessary if it was plumbed to the outside. If this is not an option, a controlled burn system vs open fire is always going to be better. Since CO it's related to the completeness of the burn, which is related to gunk build up, and RMHs tend to be lower than wood burners in this department, RMHs would theoretically be safer. Gases are also controlled because they are made for modern homes.  As much as I love our wood burner, if I wanted to build a pittly unsafe fire on a semi cold day which could back draft in side, especially after I insulate the house, I could. My knowledge will hopefully prevent stupid accidents and if I can insulate the house as completely as I wish I will probably plumb to the outside. However, there are a number of health issues related to good insulation (radon, H2O, CO, CO2, off gassing, etc.). I am watching to get the right balance, but on average, I'm not average, so on average I'd say if you got good insulation, plumb to the outside and call it a day. Oh, and on insulation: just because you hired someone to blow junk in your walls doesn't mean you have good insulation. It just means you potentially do. See my post on houses sucking for more on that rant. And, always have atleast one carbon monoxide sensor in any case. $30 is better than a last accident.