Pellet Stove combustion and Carbon Monoxide

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arnash

arnash

New Member
Jan 24, 2011
228
land of giant redwoods, No.Calif
nc-wow.com
In the now-locked thread about altered stoves dbailp wrote:
"I never read of CO poisoning from a pellet stove, i have read much about a pellet stove leaking in the house & the stink."
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That's always the case with pellet stoves, if your stove could put out CO it wouldn't be produced by itself because the stink of burning wood would accompany it. The kind of stove that can produce lethal amounts of CO is a gas heater, unvented to the outside. That's why they're illegal in California (and other states as well I'd guess). I'm not familiar with oil furnaces but assume they're even worse.

Smokey wrote:
"Unfortunately any device that burns a carbon based fuel will generate CO, and as always it is a matter of concentration and an individual’s ability to tolerate what they are exposed to.

Normally what folks notice is what happens when the stove is not burning correctly or is in the start up stage and there is an installation, maintenance, or improper operation issue.

ETA: Here is a link on wood pellet combustion products (they do not break down the many compounds in the component called TOC, there are however extremely detailed analysis of combustion products in various technical reports and studies).

http://docs.google.com/viewer?a=v&q...9Mihuc&sig=AHIEtbRWui8YmMnGrVnmaQ30RX-Zwv1wIw
Click to expand...

The above link with take you to "English Handbook for Wood Pellet Combustion" -the definitive work on the subject, translated from Danish. It's a scientifically complete analysis of the subject. What stands out in the section that I read about combustion follows:

"Gasification (pyrolysis)
With further heating, the wood pellets start to emit gases. At approximately 270 °C
gasification will produce the heat necessary to continue the process. Carbon monoxide
(CO), hydrogen (H2) and methane (CH4) are created along with other hydrocarbons

Gas combustion
If there is sufficient oxygen present the gases will be ignited when they reach their
ignition temperature. The hydrogen will react with oxygen and create water and the
carbon of the hydrocarbons and the carbon monoxide will burn into carbon dioxide and
water vapor. If the temperature is not high enough or there is not enough oxygen to feed
the combustion, the gasses will be seen as smoke that will burst into flames, when the
temperature or the inflow of oxygen is increased."

It states that Carbon Monoxide is converted into CO2, so I guess that would mean that a stove that isn't vented to the outside may poison you from it's fumes but one of them isn't CO. It would be like sitting near a campfire and breathing its awful smoke, something that few can tolerate (unless they smoke 3-4 packs a day). I'd say that's some good news.
 
I think something was lost in translation.

CH4 + 2 O2 → CO2 + 2 H2O

This is a simple combustion reaction for methane. This applies to combustion in general. For this reaction, CO is not turned into CO2, rather, CO2 is made directly.

Under conditions where oxygen isn't present in high enough quantities (or at the right place at the right time) a different reaction takes place creating CO

2 CH4 + 3 O2 → 2 CO + 4 H2O

Since perfect combustion is not easy, especially w/ solid fuels, the products of most combustion are a mixture of these two.

Now, in the right conditions where it is hot enough and there is still additional oxygen present the following can occur

2 CO (g) + O2 (g) ----> 2 CO2 (g)

Both CO2 and CO will asphyxiate you. With CO2 if you get out of the environment you can quickly recover (IE you hold your breath too long and pass out) The real danger w/ CO is that it has the ability to bind w/ your hemoglobin right where O2 is supposed. Over time, this decreases your bloods ability to even attempt to carry oxygen which is why recoving from CO poisoning is not easy.

Point to all of this? Our beloved heating appliance create gasses that can poison us to the point of death. That fact should not be taken lightly especially when considering modifications.

pen
 
pen said:
I think something was lost in translation.

CH4 + 2 O2 → CO2 + 2 H2O

This is a simple combustion reaction for methane. This applies to combustion in general. For this reaction, CO is not turned into CO2, rather, CO2 is made directly.

Under conditions where oxygen isn't present in high enough quantities (or at the right place at the right time) a different reaction takes place creating CO

2 CH4 + 3 O2 → 2 CO + 4 H2O

Since perfect combustion is not easy, especially w/ solid fuels, the products of most combustion are a mixture of these two.

Now, in the right conditions where it is hot enough and there is still additional oxygen present the following can occur

2 CO (g) + O2 (g) ----> 2 CO2 (g)

Both CO2 and CO will asphyxiate you. With CO2 if you get out of the environment you can quickly recover (IE you hold your breath too long and pass out) The real danger w/ CO is that it has the ability to bind w/ your hemoglobin right where O2 is supposed. Over time, this decreases your bloods ability to even attempt to carry oxygen which is why recoving from CO poisoning is not easy.

Point to all of this? Our beloved heating appliance create gasses that can poison us to the point of death. That fact should not be taken lightly especially when considering modifications.

pen
Click to expand...

Pen:
I'd like to elaborate on your chemistry and description a bit.

CO2 in non-toxic. It is the gas Coke and Pepsi and those types put in soda-pop. The problem with Co2 is it replaces O2 (oxygen) in the air around us. More CO2 --> Less O2. Our bodys work well in air which is about 19% O2, 79% N2, 1% Argon and 1% bad stuff (like CO and other emissions). The problem is - when CO or CO2 increase in the air everything else drops. At about 16 to 17% O2 we (people) begin to gasp for air.

Now CO has the additional problem over CO2 - in that it ties direclty with our hemoglobin - therefore the O2 cannot tie and our bodies (cells) are starved of O2.

Certain combustion reactions favor CO2 and H2O formation over CO. One is the burning of propane gas (C3H8) in an internal combustion engine. That's why some forklifts can be used inside of a building with minimal venting to the outside.

Great chemistry discussion here!

RonB
 
So is the Carbon Monoxide detictor that I have in the same room as the stove even going to detect if the stoves exhust were to start leaking into the room? What is the best detection method?
 
The temperature is insufficient in a pellet burning device to cause all of the CO produced to further undergo oxidation into CO2.

CO2 is an essential gas for life on this planet and it takes a very high concentration before it displaces enough of the other gases in the air to cause problems for people.

Be very careful in assuming any burning device even comes close to operating as theory provides via possible chemical reactions. A pellet burning device does not consume all of its fuel in the highest temperature portion of the device.
 
BradH70 said:
So is the Carbon Monoxide detictor that I have in the same room as the stove even going to detect if the stoves exhust were to start leaking into the room? What is the best detection method?
Click to expand...

In most circumstances a properly placed and maintained carbon monoxide detector will save your life. If you have major health issues with your lungs or heart you have to be certain that the detector has a low enough detection limit for sounding its alarm.
 
pen, one should also point out that even using other fuels perfect combustion is close to impossible. Traces of other than the primary target of combustion carbon is present in the fuel, this can all by itself present major problems with combustion.

One of which a lot of folks have already encountered, namely my good buddy the clinker, all kinds of nasty things happen when those puppies show up in the burn pot.
 
dbailp said:
i think coal smoke is mostly co & co2 & doesnt stink?
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Coal has its own burning odor (and other burn related issues) because even low sulfur coal can produce a bit of various sulfur compounds that stink (and are highly corrosive).
 
A very long time ago I worked on a type of blast furnace called a cupola. It's was water cooled, continuousally running, and coke fired. The operating tempeture internally was 2400-2800 F. It wasn't unusual to reach concentrations of 500 ppm of CO on the charging floor. Take my word for it, it is very dangerous. Low levels of exposure over a period of time can lead to serious medical problems.
 
So I guess the moral of the story is to have sufficient smoke detectors and CO detectors through out your house, and if you haven't changed batteries in a while this maybe a good time to do so.

To many horror stories of CO deaths when they are avoidable!
 
My wife and I cleaned all the smoke detectors in the house and replaced all the batteries on the New Year weekend. The CO detector plugs into an outlet so no need to worry about drained batteries in it.

One thing that I have notice a few times is that when the stove in running at a higher heat level (controlled by the t-stat) is that if the oil furnace kicks on at the same time, there is a slight smell of exhaust fumes in the basement. The problem is that the furnace is directly below the main living space in our house. Makes me wonder if when the pellet stove is running at the higher heat level that it is creating enough negative pressure in the house to cause some of the furnace exhause to escape from the flue pipe.

I currently do not have an OAK installed on the stove. I was planning on hooking one up this summer, now I am DEFINATELY going to install one before the next heating season begins. I have an insert in a masonry fire place, so it will be a bit of a challange, but I have a couple of ideas that may work. Maybe I will post my ideas on the forum and see what kind of responses I get.
 
dbailp said:
Bank said:
So I guess the moral of the story is to have sufficient smoke detectors and CO detectors through out your house, and if you haven't changed batteries in a while this maybe a good time to do so.

To many horror stories of CO deaths when they are avoidable!
Click to expand...
with a name like Bank i can see how thats your moral of the story. money dont grow on trees
Click to expand...

If you haven't priced it lately, a funeral is a heck of a lot more than a couple of CO detectors. With a safe install the risk is quite low but not negligable.
pen
 
dbailp said:
Bank said:
So I guess the moral of the story is to have sufficient smoke detectors and CO detectors through out your house, and if you haven't changed batteries in a while this maybe a good time to do so.

To many horror stories of CO deaths when they are avoidable!
Click to expand...
with a name like Bank i can see how thats your moral of the story. money dont grow on trees
Click to expand...

If you can afford a pellet stove or to buy pellets you can afford a CO detector.
 
dbailp said:
SmokeyTheBear said:
dbailp said:
Bank said:
So I guess the moral of the story is to have sufficient smoke detectors and CO detectors through out your house, and if you haven't changed batteries in a while this maybe a good time to do so.

To many horror stories of CO deaths when they are avoidable!
Click to expand...
with a name like Bank i can see how thats your moral of the story. money dont grow on trees
Click to expand...

If you can afford a pellet stove or to buy pellets you can afford a CO detector.
Click to expand...
have to buy the pellets too. the pelltsmoke stinks & even the coal smoke stinks but i still need to fill the house with co detectors & at the expense of what when no money ?
Click to expand...

Well the normal cure for no money is to get a job and earn some.
 
CO detectors can be had for less than $40 at big box stores, or online. That's a small price to pay to keep you and your family out of the ER, or even worse, a coffin/funeral. ER copays (if you're insured) will run you 5x the cost of a CO detector, if you're uninsured you'll be financing an ER bill for years. Finances aside, the safety issue itself is the most important factor here, these inexpensive devices are life-savers.

Here's one that plugs right into a power outlet and also uses a battery backup, $35 on Amazon.com:
http://www.amazon.com/Kidde-KN-COPP...N86A/ref=sr_1_2?ie=UTF8&qid=1301508061&sr=8-2

Here's another one for $30:
http://www.amazon.com/First-Alert-C...VMKG/ref=sr_1_1?ie=UTF8&qid=1301508061&sr=8-1

You don't need to "fill your house" full of CO detectors. Having just ONE is infinitely better than not having any at all. Generally speaking, most households have two CO detectors, one right near the furnace/pellet stove, and another just outside of a bedroom so that there are no problems hearing the alarm go off at night when everyone in the household is sound asleep. My own house is a new-build, all of the detectors are hard-wired (including the CO detector), if one goes off, they all go off.
 
CO is odorless, colorless, etc., so unless you have superhero abilities, you cannot smell CO. Just because you cannot smell exhaust fumes does *not* mean that you do not have a CO leak issue.
 
I'm not sure what the conversation is about but I hope nobody is arguing that their pellet stove does not produce massive amounts of CO. That is why anything that burns wood is anything but "green".

The likelihood of being poisoned by your pellet stove is next to nill due to the fact that it's been tested and designed in such a way to be resistant to just such a thing but also the fact that's it's a forced draft but to elaborate a little more, your stove is actually under a constant vacuum.

More importantly, you will notice that your stove generally has 1 continuous stamped or cast piece after the blower so that that no "positive pressure" leaks develop in the stove itself. The rest of the stove before the blower is under vacuum and thus it's really impossible to develop anything but at an air leak into the stove itself.

And generally yes, Natural Gas and propane both burn very clean in regards to the amount of CO and HC's they produce. That is why indoor equipment is run off of propane or natural gas and generally has no aftertreatment device on the exhaust.
 
Just a reminder. While you know to change the batteries in those Carbon monoxide and smoke detectors, remember that the detectors also predictably deteriorate and became unreliable. I recently replaced mine with units that have a battery that last the life of the unit, and better yet, no removable battery, a major reason for for detector failure. (someone wants the battery for a game or toy, or doesn't like the false alarms.) If you have one with the replaceable batteries or is hard wired, I think the current shelf life is 10 years.
 
True, I used to own a Kidde Night Hawk CO detector that plugged into the power outlet, after about 6 years it quit with a constant "Err" on the display. I checked the manual and sure enough discovered it had reached the end of its life, had to be thrown out. Many of the new CO detectors do a self-test every so often, so the detectors know when they have deteriorated to the point of being unreliable and shut down permanently.
 
While it's true that the stove runs with a negative pressure (vacuum) inside, the stove isn't even a concern, but the vent system is because it is under a slight positive pressure. But I can say from my experience, that when your vent joints aren't sealed well with silicone, you are going to notice it because the exhaust gases stink! So I'd wager that it is impossible to get enough CO into your system from a vent leak unless you're unconscious because the acrid toxic sooty fumes of combustion will probably wake you up. But that guess comes with two reservations; that one wouldn't want to risk the lives of their loved ones while running a stove 24/7 because being wrong would be disastrous, and 2: what are the odds of a leak developing in a vent system that has no leaks? Damn near zero I'd guess (until the Big One hits) So for a solo fellow, especially one that doesn't run the stove at night, not having a CO detector is no big deal. But not having a Fire & Smoke Detector is a big deal because of fires from unforeseeable sources (bad wiring, for one)

And while on the CO subject, if I had to wager that no one can site a case of a death from CO poisoning due to a pellet stove, I think I'd probably win. So on the side of not sweating CO poisoning from a pellet stove are the facts that 1. the stove is under negative pressure 2. Sealed vent systems will remain sealed and not leak CO alone without the other stinking combustion by-products that your nose will detected probably even before a CO detector could detect CO. 3. Even if a vent has a leak and nothing is done to fix it immediately, you'll get sick of breathing the stinking acrid gases before CO will impair your faculties.

And remember, CO deaths from faulty vents are linked to gas heaters -which lack the stinking combustion by-products that would alert one to the toxic situation. With all that in our favor, one still has to ask oneself if they have confidence in the mounting brackets of their vent pipe if located in earthquake territory. It's possible to sleep through an earthquake, though I don't know that from experience since all the major quakes I've experienced in So. Calif were in the day. (Here I thought I was escaping earthquake danger by moving to near the Oregon border, but then learned that the massive Circadian Fault is not far off shore and hasn't ruptured in a few hundred years. Man, am I ever not ready for that. But hey, I've survived a big one before)
P.S. CO, if I remember right, has 30 times the strength of oxygen to bind to hemoglobin, which is what makes it such a powerful gas at causing unconsciousness .
 
Don't even like this thread. Doomed from the very start....
Stoves.... Negative pressure, Yes... (modern stoves)
Vent pipe..... Positive pressure, Yes...
Pellets burning...... Producing CO, Yes....
Anyone who wants to take the "Gamble", that there Smarter than a CO detector....... STUPID!!!!.... PERIOD.

IF "IT" burns, then "IT" produces CO, therefore "IT" can kill you.

To think that one could outsmart the physics, is just plain stupid. I have 3 CO detectors. 3 Fire/Smoke detectors. 2 of each are battery operated, the other 1 & 1 are powered by standard 120v (CO is plug-in, Smoke is hardwired) both with a battery back-up. Life is to important for me to "Guess" when I am gonna be Lucky and smell my Death coming. My neighbor has No sense of smell. He also has several CO and Smoke detectors. He was born without the sense of smell. 39 yrs old and doesn't know what Bacon smells like (what a shame). Ask him if he can smell the "Death" from his woodstove.

Spend the money and for God's Sake. You spent big money on a stove and venting. If you can smell your pellet stove and don't know what your doing. Have your stove looked at by a Professional. For YOU and/or your FAMILY (if you have one).
 
After reading and commenting on both threads in question I would have to believe the concept of CO was proved beyond any reasonable doubt. The chemical chart (although making my head ache) was precise and to the point. Anyone who can't grasp the concept by this point will never understand or is just argueing for the sake of argueing.
 
TLHinCanada said:
After reading and commenting on both threads in question I would have to believe the concept of CO was proved beyond any reasonable doubt. The chemical chart (although making my head ache) was precise and to the point. Anyone who can't grasp the concept by this point will never understand or is just argueing for the sake of argueing.
Click to expand...

Agreed. And in being well answered it's time to put her to bed.

pen
 
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