Ways to burn cleanly

[begreen]

This letter was posted on the Alliance for Green Heat's FB page. I thought it was worth sharing here. It brings up very good points. It's often not the stoves, but the fuel, draft, and how the stoves are run.

Letter: Ways to clean up wood burning

The trouble is, laboratory testing and real world operation are two different situations

www.cowichanvalleycitizen.com

 

[jalmondale]

Is there any data to back up that top-down fires have less particulate during start-up than bottom-up? I've found a combination bottom-up plus front-to-back to be far and away the most effective way to get my flue gasses up to temp quickly to engage the cat, but I'm curious if this is something I should be experimenting with further (I have tried the top-down method a few times, with fairly lackluster results - many people seem to like that approach, though, so it could easily have been operator error). Typically the flue probe hits 500 in 5 - 15 minutes after a reload (most of the time in less than 10), and I've never had it take longer than 20 (much less 'sputter and spew for hours'). That seems in line with the timing in the stickied post about operating an EPA stove, but maybe I'm misreading that post? Once the cat is engaged, there's no visible smoke from the chimney, and I can't usually smell anything, which seems to pass the letter-writer's test, but if there's a noticeably faster way to get up to full-combustion-temps (or if there are different ways to get there that release different amounts of particulate), I'm certainly happy to try it out.

Edit: I figured I'd add a photo of what I mean by how I'm loading the stove - it's side loading, so the front with the air wash is to the left in the photo. I was able to engage the cat about 7 minutes after lighting the match to kick this off.

 

[snobuilder]

"The trouble is, laboratory testing and real world operation are two different situations" ....LOL....of course! Thats why testing a stove and then putting it into production and then into the final setting removes it from the test by 180 degrees. So many variables yet it is called gospel by some.

"automatic draft control".....Like on my 13 YO wood furnace....LOL


With my modifications I get to the secondary burn in a matter of minutes. Dry wood is the key.
If the author was my neighbot he'd have less to whine about.

 

[clancey]

I think that writing with the article was well done but I do like jalmondale's loading...I had three very good experiences with stoves and maybe two bad to where I am looking at other fuel sources to use in my stove. I love the ambiance but not the bad that could go with burning wood especially if there is a lot of smoke and no action...So just to know the wood is dry I guess I will have to stick to something like environmental logs or another type of name and it is easier for me but more expensive too..clancey

 

[PaulOinMA]

I am currently burning punky wood to get rid of it and working through the piles of kindling branches just off the driveway.

I think I am a Romper Room Don't Bee.

 

[bholler]

"The trouble is, laboratory testing and real world operation are two different situations" ....LOL....of course! Thats why testing a stove and then putting it into production and then into the final setting removes it from the test by 180 degrees. So many variables yet it is called gospel by some.

"automatic draft control".....Like on my 13 YO wood furnace....LOL


With my modifications I get to the secondary burn in a matter of minutes. Dry wood is the key.
If the author was my neighbot he'd have less to whine about.

There are new stoves available with auto air controls just so you know. And it seems more are going that route to remove part of the user variablity. But you are missing a major point I have been trying to get across to you. One of the most important parts of the system is the chimney. It needs to be setup so it is as close as possible to the test conditions so you get optimal performance. Of course proper fuel and proper operation are both very important as well

 

[bholler]

I am currently burning punky wood to get rid of it and working through the piles of kindling branches just off the driveway.

I think I am a Romper Room Don't Bee.

Yeah I am burning up some punky stuff as well currently. Well not today. It's in the 70s today

 

[thisoldgoat]

"This is the point at which the exhaust is actually clear and free of odour."

This is a very good article, but I must disagree with the above statement. My exhaust is never free of odor. I run a hot firebox in a Drolet Myriad 1, flue temps of 600 - 900 degrees F during the most active part of the burn. Emissions are invisible but if I'm downwind of the stack my nose easily detects it. It is a much different odor, certainly, than the "cold" smoke odor emitted early in the burn cycle, but exists nonetheless.

Now, if outdoor temps are very low one can see stuff coming out of the stack, but that certainly is water vapor condensing in the cold air, not smoke.

 

[snobuilder]

"This is the point at which the exhaust is actually clear and free of odour."

This is a very good article, but I must disagree with the above statement. My exhaust is never free of odor. I run a hot firebox in a Drolet Myriad 1, flue temps of 600 - 900 degrees F during the most active part of the burn. Emissions are invisible but if I'm downwind of the stack my nose easily detects it. It is a much different odor, certainly, than the "cold" smoke odor emitted early in the burn cycle, but exists nonetheless.

Now, if outdoor temps are very low one can see stuff coming out of the stack, but that certainly is water vapor condensing in the cold air, not smoke.

I will ask again because I guess I don't know how to burn wood....how are 600 to 900 degrees up and out the chimney an efficient burn?

I know what smell you are referring to it is a hot hot metal smell....lol

 

[bholler]

I will ask again because I guess I don't know how to burn wood....how are 600 to 900 degrees up and out the chimney an efficient burn?

I know what smell you are referring to it is a hot hot metal smell....lol

They shouldn't be running that hot at all normally. 900 is the absolute top of what I like to see. Typical cruising temps are 450 or 500 internal temps which normally keeps you just above the condensation point at the top of the chimney. If the chimney is really well insulated you can run lower. If it's exterior clay or an air cooled chimney possibly a bit higher. It doesn't matter what stove it is those are the temps required to avoid creosote buildup. But no 600 to 900 is not stressing any of the metal excessively. Just wasting heat

 

[EbS-P]

Is there any data to back up that top-down fires have less particulate during start-up than bottom-up? I've found a combination bottom-up plus front-to-back to be far and away the most effective way to get my flue gasses up to temp quickly to engage the cat, but I'm curious if this is something I should be experimenting with further (I have tried the top-down method a few times, with fairly lackluster results - many people seem to like that approach, though, so it could easily have been operator error). Typically the flue probe hits 500 in 5 - 15 minutes after a reload (most of the time in less than 10), and I've never had it take longer than 20 (much less 'sputter and spew for hours'). That seems in line with the timing in the stickied post about operating an EPA stove, but maybe I'm misreading that post? Once the cat is engaged, there's no visible smoke from the chimney, and I can't usually smell anything, which seems to pass the letter-writer's test, but if there's a noticeably faster way to get up to full-combustion-temps (or if there are different ways to get there that release different amounts of particulate), I'm certainly happy to try it out.

Edit: I figured I'd add a photo of what I mean by how I'm loading the stove - it's side loading, so the front with the air wash is to the left in the photo. I was able to engage the cat about 7 minutes after lighting the match to kick this off.

View attachment 293137

For me a good top down fire is 1/4 to 1/3 of the firebox full clear to the top of kindling. At a small fire starter light close the door. Reload in 2-6 hours.

Absolutely think top down is cleaner but have no data. You can get the secondary combustion rolling in 5 minutes. No the stove is not up to temp yet on a cold start but it gets there quickly. On a reload I always start with 3 pieces of kindling on the coals and another two right on top to kick that secondary combustion off ASAP.

My first thought on your picture was there is not enough wood and kindling in that load. Is getting warm out so I understand if that a smaller load but the fewer times you add wood the less smoke goes out the stack unburned.

 

[bigealta]

Is there any data to back up that top-down fires have less particulate during start-up than bottom-up? I've found a combination bottom-up plus front-to-back to be far and away the most effective way to get my flue gasses up to temp quickly to engage the cat, but I'm curious if this is something I should be experimenting with further (I have tried the top-down method a few times, with fairly lackluster results - many people seem to like that approach, though, so it could easily have been operator error). Typically the flue probe hits 500 in 5 - 15 minutes after a reload (most of the time in less than 10), and I've never had it take longer than 20 (much less 'sputter and spew for hours'). That seems in line with the timing in the stickied post about operating an EPA stove, but maybe I'm misreading that post? Once the cat is engaged, there's no visible smoke from the chimney, and I can't usually smell anything, which seems to pass the letter-writer's test, but if there's a noticeably faster way to get up to full-combustion-temps (or if there are different ways to get there that release different amounts of particulate), I'm certainly happy to try it out.

Edit: I figured I'd add a photo of what I mean by how I'm loading the stove - it's side loading, so the front with the air wash is to the left in the photo. I was able to engage the cat about 7 minutes after lighting the match to kick this off.

View attachment 293137

My eyes show me, my top down starts with very little smoke and very fast start of secondary flames. In a non cat stove the starting of robust secondary flames is the key to clean starts that move to clean burns. The bottom splits might not even be warm at the time of secondary establishment, but the firebox is burning cleanly. Bottom up starts shows thick smoke if loading with anything bigger than kindling.

 

[bigealta]

Start at the 4 minute mark and you can see for yourself the minimum smoke this top down set up creates.

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[begreen]

Is there any data to back up that top-down fires have less particulate during start-up than bottom-up? I've found a combination bottom-up plus front-to-back to be far and away the most effective way to get my flue gasses up to temp quickly to engage the cat, but I'm curious if this is something I should be experimenting with further (I have tried the top-down method a few times, with fairly lackluster results - many people seem to like that approach, though, so it could easily have been operator error). Typically the flue probe hits 500 in 5 - 15 minutes after a reload (most of the time in less than 10), and I've never had it take longer than 20 (much less 'sputter and spew for hours'). That seems in line with the timing in the stickied post about operating an EPA stove, but maybe I'm misreading that post? Once the cat is engaged, there's no visible smoke from the chimney, and I can't usually smell anything, which seems to pass the letter-writer's test, but if there's a noticeably faster way to get up to full-combustion-temps (or if there are different ways to get there that release different amounts of particulate), I'm certainly happy to try it out.

Edit: I figured I'd add a photo of what I mean by how I'm loading the stove - it's side loading, so the front with the air wash is to the left in the photo. I was able to engage the cat about 7 minutes after lighting the match to kick this off.

John Gulland did some extensive research on this in Canada. I will see if I can find his research. The conclusion was that top-down was the cleanest.

Pointdexter is in the very smoke-sensitive area of Fairbanks, AK. He wrote up a pretty detailed writeup of what was the quickest way to achieve smoke-free burning several years back.

Anecdotally, I see this with most cold starts in our stove, especially during low-pressure weather. We live on a slope. When starting our stove during a low barometer the smoke doesn't go up, it rolls down the hill and I see it descending in a fuggy cloud. Fortunately, there are woods across the road, but it's embarrassing. The visual difference and time before this smoke roll-out stops are quite noticeable. With a bottom-up start, it can go on for 30 minutes, and looks like a fog has hit the neighborhood. With top-down starting, I have it down to about 10 minutes depending on the kindling used.

 

[snobuilder]

2 large splits rt and left form valley where 2 sheets crumpled paper and various size kindling go then small to medium splits on top straddling all. Gets to a secondary burn in 5 to 10 minutes and clean vapor within 30 minutes.

 

[jalmondale]

For me a good top down fire is 1/4 to 1/3 of the firebox full clear to the top of kindling. At a small fire starter light close the door. Reload in 2-6 hours.

Absolutely think top down is cleaner but have no data. You can get the secondary combustion rolling in 5 minutes. No the stove is not up to temp yet on a cold start but it gets there quickly. On a reload I always start with 3 pieces of kindling on the coals and another two right on top to kick that secondary combustion off ASAP.

My first thought on your picture was there is not enough wood and kindling in that load. Is getting warm out so I understand if that a smaller load but the fewer times you add wood the less smoke goes out the stack unburned.

Yeah, that was a smaller load because of the outside temps - I still didn't need to reload for about 8 hours. I'm not sure I'd be ok sacrificing 1/3 of my firebox to kindling to shave 2 minutes off my startup time, though - that does explain why I might have not had great results with top-down if it needs a lot more kindling than bottom up (I've only got 1.85 cu ft to work with, so when it's not 50 degrees out I need all that space). Might be useful for spring/fall, especially since that's when it takes a little longer to get the stove up to temp.

It sounds like the consensus is that 5-10 minutes is a typical good startup time, and that 20+ would be a problem, so it seems like my approach is getting decent results as far as time-to-engage-the-cat goes. I'll also do some googling for the John Gulland data, that would be interesting to read.

 

[begreen]

It sounds like the consensus is that 5-10 minutes is a typical good startup time, and that 20+ would be a problem,

I would say more like 10-20 minutes for a quick cold start. It takes time to get the firebox and mass of the stove up to temperature.

I'll also do some googling for the John Gulland data, that would be interesting to read.

I may be misattributing this to John, it's been a long time since I read this article. If so, my apology.

Where there's no smoke, there's fire: Time to turn your woodburning upside down? - MinnPost

It's easy to get official advice about choosing a clean-burning woodstove or selecting the best logs — but perfect fuel and equipment can't overcome the built-in flaws of traditional firebuilding techniques.

www.minnpost.com

The steps:

A non-commercial service in support of responsible home heating with wood - Top-Down Fires Step-by-Step

The Wood Heat Organization was formed to support the public in the responsible use of wood energy in the home. We fulfill our mandate by providing reliable information, by conducting research into wood heating-related issues and by representing the public interest in discussions of policies that...

woodheat.org

This is a good read.

https://www.mha-net.org/docs/v8n2/docs/TOPDOWN.pdf

 

[bigealta]

Yeah, that was a smaller load because of the outside temps - I still didn't need to reload for about 8 hours. I'm not sure I'd be ok sacrificing 1/3 of my firebox to kindling to shave 2 minutes off my startup time, though - that does explain why I might have not had great results with top-down if it needs a lot more kindling than bottom up (I've only got 1.85 cu ft to work with, so when it's not 50 degrees out I need all that space). Might be useful for spring/fall, especially since that's when it takes a little longer to get the stove up to temp.

It sounds like the consensus is that 5-10 minutes is a typical good startup time, and that 20+ would be a problem, so it seems like my approach is getting decent results as far as time-to-engage-the-cat goes. I'll also do some googling for the John Gulland data, that would be interesting to read.

1/3 of firebox kindling is overkill, not needed. It will speed up time to high heat if that's your goal. But to get clean burning with low smoke you don't need nearly that much.

Again see for yourself below, in what i call aggressive top down made with not much kindling and mostly large splits for a Full long lasting Fire without need to reload till coaling stage. I even added some SLOW MOTION for your viewing and inspection pleasure.

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[snobuilder]

Yeah, that was a smaller load because of the outside temps - I still didn't need to reload for about 8 hours. I'm not sure I'd be ok sacrificing 1/3 of my firebox to kindling to shave 2 minutes off my startup time, though - that does explain why I might have not had great results with top-down if it needs a lot more kindling than bottom up (I've only got 1.85 cu ft to work with, so when it's not 50 degrees out I need all that space). Might be useful for spring/fall, especially since that's when it takes a little longer to get the stove up to temp.

It sounds like the consensus is that 5-10 minutes is a typical good startup time, and that 20+ would be a problem, so it seems like my approach is getting decent results as far as time-to-engage-the-cat goes. I'll also do some googling for the John Gulland data, that would be interesting to read.

I. Well chit ...ill just leave this here....
Wood burning is not an exact science. Never has been. Never will be. To buy into any or all fire start and build fire suggestions from a single source is true idiocy. YOUR RESULTS MAY AND WILL VARY. Despite the EPA involvement.
Variables abound. The more control you have over them is the key to safe burning.

 

[stoveliker]

I believe that I read that @Poindexter uses a few pounds (3 or 5) of kindling to get up to (cat) temperature quickly. I don't use that much either (and can get my cat engaged in 5-10 minutes -- I know cat temps are different than secondary burn temps, and thus a comparison with the discussion here is not very meaningful but: )

I think a lot of this depends on ones definition of kindling, ones flue set up, ones stove, and the dryness of wood and kindling (and the weather, tightness of the home etc etc).

It's nevertheless good to read how others do things well. Try things out for yourself, and stick with what has the best results in your situation.

 

[Bobbob]

I do believe all this is great information. I've been burning a full year now with my first epa certified insert ( Buck model 81). I have been learning best practices for starting and maintaining a good clean fire with this secondary burn type stove. I have found just about everything that can, will affect both a cold start and burn time. My wife thinks I'm crazy every time I suggest trying something else, but it has been an interesting learning experience that has definitely developed from reading these forums. Thanks to everyone that takes the time to share information so we all can strive to burn efficiently and responsibley. Having a fire to stare at and enjoying the heat are the two things that make cold weather bareable.

 

[qwee]

I read somewhere where some burning pros hooked up their analyzers to see which starting method produced the least pollution. I think they were testing in masonry heater fireboxes in Austria. They figured this would be the top-down method. It made sense - the gasses have to pass right through the flames. They were surprised to find that they got the least amount of pollution (overall) from a different starting method.

The key was to get the fire going and hot ASAP. The top-down method is slow - it takes time. A side fire with lots of kindling and using a torch gets things going quickly, and temps go up faster thus burning more off gasses. If I remember right, this ASAP method created more pollutants initially but it went cleaner faster than the top-down method.

So this ASAP side fire with a torch created less pollution overall - these burning pros were surprised. Most people are convinced the top-down method is the best way - and if it makes people feel good to think they are creating less pollution that is good. But, I'm going with the ASAP method because the data says it is less polluting - though it requires more work and you need a torch. Maybe the other studies go against this. I don't know.

 

[bigealta]

I read somewhere where some burning pros hooked up their analyzers to see which starting method produced the least pollution. I think they were testing in masonry heater fireboxes in Austria. They figured this would be the top-down method. It made sense - the gasses have to pass right through the flames. They were surprised to find that they got the least amount of pollution (overall) from a different starting method.

The key was to get the fire going and hot ASAP. The top-down method is slow - it takes time. A side fire with lots of kindling and using a torch gets things going quickly, and temps go up faster thus burning more off gasses. If I remember right, this ASAP method created more pollutants initially but it went cleaner faster than the top-down method.

So this ASAP side fire with a torch created less pollution overall - these burning pros were surprised. Most people are convinced the top-down method is the best way - and if it makes people feel good to think they are creating less pollution so that is good. But, I'm going with the ASAP method because the data says it is less polluting - though it requires more work and you need a torch. Maybe the other studies go against this. I don't know.

So that was in masonry heater? Did it have secondary tubes? Does not sound like this (if accurate and true) is applicable to a woodstove with secondary reburn baffle / tubes.

 

[thisoldgoat]

I will ask again because I guess I don't know how to burn wood....how are 600 to 900 degrees up and out the chimney an efficient burn?

I know what smell you are referring to it is a hot hot metal smell....lol

Thanks for the tip snobuilder; I'll burn at a lower temp and see if the aroma disappears.

 

[thisoldgoat]

They shouldn't be running that hot at all normally. 900 is the absolute top of what I like to see. Typical cruising temps are 450 or 500 internal temps which normally keeps you just above the condensation point at the top of the chimney. If the chimney is really well insulated you can run lower. If it's exterior clay or an air cooled chimney possibly a bit higher. It doesn't matter what stove it is those are the temps required to avoid creosote buildup. But no 600 to 900 is not stressing any of the metal excessively. Just wasting heat

I owned a chimney fire once upon a time and it may have left me a bit paranoid. So... I tend to let flue temps hover on the high side of the thermometer's happy zone. I'll turn it down some. Thanks