Secondary Burn

[cpop]

Hi All,

I searched through all the existing threads, but can't seem to find answer for secondary burn question so hopefully someone here can help me out. How long on average would you say secondary burn lasts? I have 4 baffles on my insert, when I damper down I will see flames all across the rear baffle, but the 3 closest to the front don't show any flames. This last for 10-20 min. I placed a thermometer on the top of the insert where the fan blows out (Hampton 300) and I do see the temp go up about 150 degrees once I damper it down. Flames dance around the logs, but not at top of stove.

Originally I was thinking my wood wasn't seasoned well enough, but then I tried with BioBricks and experienced the same results. Even dampered all the way down the bios will burn for 3-4 hours, then just glow with no action at top of insert. Perhaps the Bios don't emit enough smoke for secondary burn?

 

[wahoowad]

sometimes sometimes sometimes

Sometimes I get a full blast of secondary burn out of all my tubes, but more often than not it is less than that. Varies. Mine can dance around a lot, getting sprays of secondar burn in different areas, other times getting a consistent output from say 25% of the available area. What I do not get is full seconday burn all the way across the tubes for hours and hours at a time. I have a cycle where it happens for awhile, then I think most of the gasification has happened.

 

[swestall]

I would say you are getting it if you see no smoke out the stack. It isn't always a pretty light show, but its working. Key is smoke or no smoke. Also agree that if gassification is done, no smoke no visible burn.

 

[Moohooya]

I'm have a Lopi Endeavor and I'm having trouble getting the secondary burn going. I can get the stove hot enough, 600F, 300C, but I can't get the tubes to stay lit up. If I open up the air control and get the fire roaring, and then close up the air control 3/4 of the way, the whole fire box lights up along with secondary burn tubes. However within a minute or two the tubes go out, although the fire continues to lethargically burn. Am I still getting complete combustion when the stove is reading 600F even though I'm seeing little if anything in the way of flames, or are unburnt gasses going up the flue due to a lack of oxygen?

I do have a tall chimney (likely a little over the recommended 15-33 feet in the manual), and I think I have an excellent draft. I've not sealed the stove pipe to the stove with cement, and there is a small whistle at the join when the the fire gets going; does this need sealing? I only have a single 90 degree bend between the stove and the chimney.

A final question, how do I get the most amount of heat out of the wood? The stove is in the basement and appears unable to get the basement too hot, and since I also have a boiler to kick in upstairs I'm looking for efficiency rather than comfort. Should I refill it while it is still hot, say 500F, or wait for it to cool down more? I seem to be getting through alot of wood.

Many thanks

 

[Rich M]

how do I get the most amount of heat out of the wood? Should I refill it while it is still hot, say 500F, or wait for it to cool down more? I seem to be getting through alot of wood.

Welcome to the forum.

500 is too hot for reloading. You don't want to "feed the fire" that is a wood waster. A large part of the burn cycle is the coaling stage. Let the coals burn down quite a bit and try reloading around 200-300F.

 

[begreen]

How does the stove burn if you close the air damper down 1/2 way instead of 3/4 closed? Is the stove hard to control or is it very responsive to the air damper? How tall is the stack? Rich has it right about reloading. Add wood when there is a good coal bed to restart the new wood, with a stove temp about 300.

 

[Corie]

Speaking of the wood, is it try and seasoned? I've seen similar results from using wet wood. Don't ask how I know

 

[elkimmeg]

First of all there is only one stage of the burning process you see for secondary burning It begins as part of stage 2 of the burn cycle after the stove is hot enough
and your wood looks charred on the outside. You begin the process of dampering down and closing your primary air secondary combustion needs two elements.
fire box temps of over 1000 ( not to be confused with surface temps) and the presents of smoke particulate to be burned. At times you will achieve a light show of secondary burn
all or at some of the burning tubes. Other stoves that use a down draft mode the smoke path is forced down over the hot coals and some particulate is burned off as it passes threw the coals the remaining particulate burn off occurs in a secondary combustion chamber

the burn tube secondary technology has to be at 1000 degrees or over if it dropps below there is no burning it can be an intermittent process of on and off as temps fluxuate
that does not mean smoke particulate is not being burned the hot fire box may burn off the particulate prior to making it up to the burn tubes you will see gass off flowing from you coals and wood at times that too is secondary burning. As you wood is being burnt it moves into the third stage of the burning cycle approaching coaling stage at this time most of if not all smoke particulate had been burned of exhausted off there will be not secondary burning just that nice clean glow and a few flickers of flames ,but plenty of heat

So there is only one part of the burn cycle that has secondary burning for one third of the time. The tell tale sign is if you look at your chimney and see little or no smoke you are achieving secondary combustion Don't be fooled if you see steam it may look like smoke but in reality there is very little particulate of smoke in steam

 

[Dunadan]

Once my temps get up to 600 (or closer to 700) I will shut the air on my Lopi down to about 1/2 - 3/4. "Shutting the air down" isn't technically what happens, so I hate using that term, but so long as you understand what you are doing is redirecting air through the burn tubes, not really letting less air into your insert, it doesn't matter. I find if I try to redirect the air too soon (i.e. stove top temps about 500) I will get some secondary burn, but not a good long sustained burn. For me 600-700 is the sweet spot for starting to shut things down.

I don't tend to look at the burn tubes as much as look to see if I see secondary burn anywhere in the stove. Sometimes I get the "jets" coming out of the tubes, but more often, as I get further into the secondary burn, it's just the wispy waves of secondary burn that pop up randomly throughout the stove.

Once you pass the "char" stage, and move onto the charcoal, you won't see any secondary burn.

As many have said here, my main indicator now is what's coming out of my chimney. If I don't see anything, I'm happy. If I see smoke coming out, I know I'm running too cool, and need to crank up the fire (by "opening" up the air) to get my temps up to where secondary burn can occur. I'm getting much better at it, but I still find times I see smoke coming out when I leave for work (thinking I had gotten things hot enough) and need to call the wife from the car to crank the fire up before dampering things down.

 

[Moohooya]

First of all, many thanks to everyone who took the time to respond to my post and answer my questions. It is so nice to be welcomed and have so many informative answers.

I'll start reloading at a cooler temp. I've done that a couple of times and noticed it doesn't take long to get the stove back up to temp.

My wood is a little green. I planned on building a wood shed last spring, but that never happened. The wood instead sat outside, some of it covered by a tarp but not all of it. A few pieces I put in do hiss as the water collects at an end, others pieces appear fine. I notice a huge difference in getting the stove up to temp between the dry and wet wood. The wet wood takes forever, the dry wood roars to life in just a few minutes.

If I close down the damper just 1/2 way I get a steady burn with the flames on the logs. It could be described similar to an open fireplace. I think the stove is easy to control, but being a novice, what I consider under control you may not. My normal burn cycle involves lighting the fire with the door ajar for a few minutes. I normally close up the bypass damper during this phase. My understanding is you only open this to stop smoke entering the house. I don't even open this when reloading, the smoke doesn't want to go anywhere but up the chimney. Once the firebox has been roaring for a few minutes I'll close the door and wait 10 minutes for the needle get up to 300 or so. (My thermometer is on the top front of the stove, not on the stove pipe.) I'll then close up the air to perhaps 3/4. Once the stove is up to 500 I'll close it up 1/2 to 3/4. At night I close it approx 7/8 after getting the temp up to 600+

I do see blueish flames around the coals and the logs sometimes, or the wispy flames elsewhere rather than up by the tubes. So it seems this is the smoke being burnt. As for what is coming out of the chimney, I do see something, but considering I typically have a wet log somewhere in the load, I see how it could well be water vapour condensing.

When you say 600-700 is the sweet spot for when you start to shut things down, are you running with the air control fully out up to this point? I'll certainly try bringing up the stove a little higher and seeing how this helps.

As for how tall my stack is, I'm not sure exactly what you mean by the stack. From the top of the stove to the center of the round entrance into the chimney is approx 21". From the top of the stove to the top of the roof is approx 33'. The chimney extends beyond that by a couple of feet, so I'd guess the distance from log to fresh air would be approx 35 feet. Is this what you asked?

Many thanks again

 

[Rhone]

Wet wood certainly plays havoc with secondary burn. I have trouble getting it consistent and going also when my wood is wet. The key as others have stated is look outside and if you see smoke (particularly blue) you're not secondary burning all you should. Also, I've noticed different woods seem to have a different amount of it. Stick a few pieces of dry elm in there and your secondary burn will go nuts. Red oak, and I've found Red Maple aren't particularly secondary burn types of wood. Also, the back secondary burn tube of my Hearthstone Clydesdale is definetely the most active. I think it's because the front is much hotter and secondary burn likely occuring around the front where there's plenty of oxygen and heat whereas the back logs are oxygen starved only getting the scrap oxygen left over which isn't enough for flames so they just gasify. Those gases rise up to the back secondary burn tube where they meet flames & oxygen and then light off. Anyway, that's why I think the back of my unit has a lot more secondary burn action than the front, but on occasion the front tubes will have a little secondary burn action but about 80% of it is often my back 2 tubes and I think my unit has 5.

 

[jqgs214]

I find my red oak has crazy secondaries. Much more than the cherry i've also burned.

 

[BrotherBart]

I find my red oak has crazy secondaries. Much more than the cherry i've also burned.

A little red oak action:

 

[Dunadan]

When you say 600-700 is the sweet spot for when you start to shut things down, are you running with the air control fully out up to this point? I’ll certainly try bringing up the stove a little higher and seeing how this helps.

Yes. I keep the air all the way open (or all air directed out at bottom of firebox) until my temps reach about 600. I normally don't try to get up to 700, but sometimes I don't check my temp quick enough, or the fire heats things quicker than I expected and I'll catch it approaching 700.

If I'm close to 700, I'll close the air down to about 3/4 in (for my Lopi, some stove it would be out) right away. If it's closer to 600, sometimes I'll close it down to 1/2 first, then after a little while drop it down another 1/4 (assuming I'm around and have the time to do keep an eye on things).

For the record, I open my by-pass damper anytime I load new wood (to keep smoke from entering house) and will usually leave open until the the new wood is engulfed in flame (about 3-5 minutes if I have a good bed of coals). If I'm building a fire from scratch, I'll usually leave my by-pass open for a good 15-20 minutes so I'm getting maximum draft and get my wood burning real good before shutting it down.

In the end, the stove-top thermometer rules all. This season I've learned if I go by this, and not by what it looks like is going on in the fire box, in the long-run I have a much more successful (long-burning) fire.

 

[swestall]

That fire show on the secondary burn with OAK is really pretty! Unfourtuantely, we don't have such things with the VC Neverburn system.....
When we figure out what it takes, what it looks like and how to get it, we will share it with all.
I am hoping that Elks work with VC (which I hope to participate in) will help resolve this. For now, I can only say I am totally jealous of those pretty secondary burns the folks with tube based burners are experiencing..
Happy Turkey to All....

 

[James04]

BrotherBart,

Could you please tell us. From a cold stove. What your procedure is. What I would really like to now is how long after a cold start do you close your bypass and start secondary burn. Once engaged do you set the air to your desired burn rate or do you let it burn for a while on the highest or near highest setting before dampening down further. I am starting to wish I had spent half the money on an Englander 30NC.

By the way, how come you don't have the gold trim on the door. Is that removable?

James

 

[Moohooya]

Rhonemas, I think wet wood was my problem. Just before lunch I built a fire, being careful to only use the driest wood. There is a hint of white smoke coming out of the chimney, no blue, and I seem to be getting a reasonable secondary burn. It isn't across all three tubes, fades in and out, but seems fairly good. I'm burning mostly oak, red oak I believe.

Dunadan, thanks for the numbers. It looks like the Endeavor and Revere are very similar, one being an insert and the other a stove. The fire box size is the same.

 

[BrotherBart]

BrotherBart,

Could you please tell us. From a cold stove. What your procedure is. What I would really like to now is how long after a cold start do you close your bypass and start secondary burn. Once engaged do you set the air to your desired burn rate or do you let it burn for a while on the highest or near highest setting before dampening down further. I am starting to wish I had spent half the money on an Englander 30NC.

By the way, how come you don't have the gold trim on the door. Is that removable?

James

I run by the look of the fire and the top temp and don't pay much attention to how long it takes. I use a good bit of split pine kindling to get a me a good coal bed fast and that also brings the stove up to 500 in fairly short order. When the flames on the kindling are starting to die to coals I put three or four splits on and let'er run up to 500 with the primary, no bypass on the 30, open and then back the primary down to about 25%. Most of the time it just eases up to 550 and secondary does its light show for a good while. When the fire is dancing blue flames on top of the wood I take it down to about ten percent and hit the bed.

Probably an hour dead cold to hitting the bed.

I don't like the look of the gold trim on the door and it does not fit anyway. The two times I clipped the thing on there around 400 degrees it popped off onto the hearth. The glass on the sucker is huge and unlike a lot of stoves none of it is blocked at the top by the airwash plate. I don't want anything blocking any of the view of the fire. It is decoration enough and with the contrast of the metallic brown stove body and black door it looks great to us.

 

[James04]

BB,

Thank you for sharing. I too do not, like the gold trim. That is why I asked. If it takes about an hour to get things cooking. Well then, I don't feel so bad. I am new to wood burning and thought an hour was excessive.

The pictures you posted. Are they in JPG format. I am unable to post JPG's as I get an error "The file you are attempting to upload has invalid content for its MIME type". They have been reduced to less than 300kb but still no good.

James

 

[James04]

I think I figured it out. This is as pretty a flame I can get with the down draft. Certainly not as nice as the glowing fires of the burn tubes.

 

[BrotherBart]

BB,

Thank you for sharing. I too do not, like the gold trim. That is why I asked. If it takes about an hour to get things cooking. Well then, I don't feel so bad. I am new to wood burning and thought an hour was excessive.

The pictures you posted. Are they in JPG format. I am unable to post JPG's as I get an error "The file you are attempting to upload has invalid content for its MIME type". They have been reduced to less than 300kb but still no good.

James

An hour up to temp and rolling for any wood stove isn't bad. There is a lot of mass to get up to temperature and the burning stages of wood to deal with. These things take some work but I have always thought it was worth it. I find it relaxing to not rush sometimes and just pull up a beverage and watch the pretty burn prior to the temp getting up to rock and roll territory.

 

[James04]

I'll be sure to clean the glass next time I take any photos. Here is the same fire with no flash. It seems that the camera does not record the dancing blue flames. Or perhaps the exposures just missed them by a fraction of a second.