Secondary combustion for dummies?

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leakypuppy

leakypuppy

Member
Mar 3, 2008
103
Northern NJ
Not really but my inability to observe flames originating from the secondary air tubes in my new Jotul 550 is beginning to piss me off. I've been burning my stove all day long today and I have a nice bed of coals -- the temp. is about 550. I reload with some dry wood I picked up a the supermarket, earlier in the day I picked up a few bundles of kiln dried splits from the hardware store. I load the fire box, open up the air control for about 10 minutes or so until the wood begins to char and then I knock the air down 50% and wait. Nothing, so I close the air a bit more. Still nothing. Coals are red but there is lots of blue and some yellow flames dancing around the box but NOTHING from the secondary tubes. I just check the temp again and its still around 550 degrees. My Rutland stovepipe thermometer is positioned inside the exhaust air slot which is atop the firebox. This is the recommended position from the posts I've read. My chimney is about 39', external brick and was relined when the insert was installed. If anyone could offer me some advise as to what I may be doing wrong/not doing I'd greatly appreciate it. I have sat and watched the fire for quite a while and at times I do see flames just appearing from nothing as if the air is combusting but I guess I'm hung up on the YouTube video of BeGreen's secondary combustion and the fact that i'm NOT seeing it makes me feel as if I don't know what the hell I'm doing!

I know secondary burns don't last forever but should I be getting them after a reload or is it something that will persists throughout the entire burn?

Thanks in advance for your help and advice.
 
Is there smoke coming out of the chimney? I have been using that as my indicator for correct burning, that and clean tan colored firebrick. I usually only get secondary burn when the firebox is full to the top, or when the air control is open and the fire is burning fast. It is just an idea, but I get the feeling that the wood isn't vaporizing fast enough to have enough smoke for the secondary to light off. Secondary burn or not, I don't see any smoke out of the chimney unless the stove is just started or just reloaded.
 
I've been watching the chimney as well and don't have much smoke at all. I made sure to go out and have a look earlier when I reloaded and there was no visible smoke. The bricks are tan -- my first few burns were made w/out much reading so it was no surprise that I quickly had them covered in soot.
 
BeGreen said:
https://www.hearth.com/econtent/index.php/forums/viewthread/16214/
Click to expand...

Thanks BeGreen I'd seen and read that thread.

What temp should I have my stove at for secondary combustion to take place?

Should I expect to see secondary burns on the first burn of the day or only after a reload with an established base of coals?

Thanks,
 
It could be that you are burning a lot of the gas, etc off prior to shutting the air down. Once you have the stove hot, the baffle hot, the secondary should burn the gas (smoke) that is being produced. A couple things to try. When you do the second load and the stove is HOT, try getting the new load flaming well and then shut all the way down and see if the tubes have a burning effect. If it stalls bring it back open and do it again when it gets going. Don't wait forever..
Also, if you have yellow and blue flames dancing around in the firebox that is secondary burning. It isn't the heavy secondary that you will get when the air tubes are burning like a "gas" burner but it is secondary.
Do you have the load up to the top, within a few inches of the tubes. You will get a stronger tube burn when you are loaded up and everything is flaming.
Try those experiments and see what happens.
The prior post about smoke is right on, if you have no smoke out the stack you are getting that smoke burned in the stove.
 
swestall said:
It could be that you are burning a lot of the gas, etc off prior to shutting the air down. Once you have the stove hot, the baffle hot, the secondary should burn the gas (smoke) that is being produced. A couple things to try. When you do the second load and the stove is HOT, try getting the new load flaming well and then shut all the way down and see if the tubes have a burning effect. If it stalls bring it back open and do it again when it gets going. Don't wait forever..
Also, if you have yellow and blue flames dancing around in the firebox that is secondary burning. It isn't the heavy secondary that you will get when the air tubes are burning like a "gas" burner but it is secondary.
Do you have the load up to the top, within a few inches of the tubes. You will get a stronger tube burn when you are loaded up and everything is flaming.
Try those experiments and see what happens.
The prior post about smoke is right on, if you have no smoke out the stack you are getting that smoke burned in the stove.
Click to expand...

Thanks swestall I'll give try and load up close to the tubes but I think that's what I've been doing as I always seem to bang the splits against the secondary tubes. After I reload and open the air up I should just wait until the logs are flaming, perhaps 5-10 mins and then shut the air down or is that too long?

Thanks,

-jim
 
10 minutes when it is "flaming" is usually OK. You have to develop a feel for that as your specific installation and draft are unique to your house.

If the burn stalls, then you know you have to go back to get it a bit hotter. What happens there is that the interior and baffle get up to a temp that can support the secondary combustion and it takes off.

Sometimes it will cool a bit (esp with wood that has too much moisture) and you have to repeat the process to keep it going.
 
leakypuppy what ^they^ said about the lack of smoke.

After 3 years of relentless nagging I bought this stove. And when my wife brought me to the dealer on Rt 13 in Pulaski I was a very difficult customer that questioned all these new fangled secondary burn claims.

The dealer being a great and patient man brought me outside to look at the stack...no smoke. We all know that smoke rises and where there's smoke there's fire ...right? If we know there's a fire but no smoke ya have to ask what happened to it? Well the smoke is re-burned and consumed. Now I'm burning slightly more than half the wood I was before and we are warmer too.

So yeah it was a good move getting the new stove...btw we have a QF4300st.
 
With a super tall stack (39 feet!) I am wondering if you are getting excess draft? The maximum flue height listed for this stove is 33 ft. Did your dealer discuss this with you?

Following the same steps you described, what happens if you close the air control down to 1/4 or even less?
 
BeGreen said:
With a super tall stack (39 feet!) I am wondering if you are getting excess draft? The maximum flue height listed for this stove is 33 ft. Did your dealer discuss this with you?

Following the same steps you described, what happens if you close the air control down to 1/4 or even less?
Click to expand...

There was no mention of my stack height but I recall reading the paperwork when they cleaned the chimney before installing that it was 39' and they would need a 40' ladder. I'll double check the paperwork again later. What would be a sign of excess draft? With regard to your question are you asking what happens if I close the air control to 1/4 instead of all the way?
 
Yes, I'm wondering how the stove responds to the air control being open only 1/4. Also how it responds with the air control fully closed. Does this snuff out the fire or is it still blazing strongly?
 
BeGreen said:
Yes, I'm wondering how the stove responds to the air control being open only 1/4. Also how it responds with the air control fully closed. Does this snuff out the fire or is it still blazing strongly?
Click to expand...

What appeared to be 39' on the paperwork is actually 32' and I can snuff out the fire by closing the air all the way so I would think this is normal. Any idea what temperature I need to be at in order for the secondaries to kick in? I was around 600 degrees yesterday but no joy.

Thanks,
 
I've never seen secondary burn on my stove that looks like flames jetting out of the holes in the tubes. The secondary flame is a nice floating rolling flame in the top of the stove. When the stove is really rolling, it looks like the pits of hell in there with this rolling flame all over the top half of the firebox. I can see spots where the air coming from the holes in the tubes looks like it punches holes in the flames, but it certainly doesn't look like flames coming out of the holes like gas jets.

Just thought I'd mention this in case people have different expectations of what they're looking for.

-SF
 
SlyFerret said:
I've never seen secondary burn on my stove that looks like flames jetting out of the holes in the tubes.
Click to expand...
Mine are like that when the stove is not that hot or the pieces of wood are large (little surface area), but if I get it hot (750/850F) off the glass the flames give the impression of coming from the holes.
 
OK, I don't run my stove that hot. Mine cruises around 500, and I take it a little over 600 occasionally, but try not to go over 700.

-SF
 
bokehman said:
SlyFerret said:
I've never seen secondary burn on my stove that looks like flames jetting out of the holes in the tubes.
Click to expand...
Mine are like that when the stove is not that hot or the pieces of wood are large (little surface area), but if I get it hot (750/850F) off the glass the flames give the impression of coming from the holes.
Click to expand...

Maybe I need to be using smaller pieces of wood and make sure the temp is above 700 degrees. I'll give that a try.
 
Puppy, This is going to sound a little crazy, but, maybe the wood you are buying is so dry that after the initial start up there are no gasses left to create secondary burn. Try getting a few dry, 4" to 5" oak splits and I bet it will make a difference.

Jim
 
jbrown56 said:
Puppy, This is going to sound a little crazy, but, maybe the wood you are buying is so dry that after the initial start up there are no gasses left to create secondary burn. Try getting a few dry, 4" to 5" oak splits and I bet it will make a difference.

Jim
Click to expand...

Don't laugh but I don't know if I could pick an Oak split out of a pile. I'm a total NOOB!
 
Pup, Look for splits with a reddish tint and looks sort of grainy.

Jim
 
Adding my 2 cents worth.

When I get the secondary burn going it looks how Slyferret described it. It happens when I have temp. around 400* on the external magnet mounted on the door so that is a low read compared to where you have your therm. ( My guess would be that your therm. would read 600*-700*)

Air is cut back between 50%-75%. If I go any lower I loose all flames.

There will still be some flame on the wood too.

My chimney is 15' tall.

Compared to my old insert, I do think this one is trickier to learn to operate. Any adjustment on the air makes a significant difference. It seems to take longer to balance itself out once a new load of wood has been added.

Just keep playing around with yours and eventually you will figure out where it has to be to get the secondaries going. Remember, even if you can't see flames and your chimney isn't spewing out smoke - your secondaries are operating so not to worry about a flame show. :coolsmile:
 
Bokeman - Just when I think I understand something -poof- I find out my understanding is wrong....

I thought secondary combustion was taking place even if we can't see flames shooting out of the air tubes.

I thought that secondary combustion was taking place when flames are rolling around the top of the fire box that don't seem to be attached to anything. Ie.- they are not shooting out of the tubes like torches or coming off of the logs. Just bluish orangish wafting flames that roll around the top half of the fire box....

I thought they happened when the hot air from the tubes ignited the gasses in the fire box and that that ignition could happen anywhere within the fire box.

So secondary combustion is ONLY happening when flames are shooting out of the tubes???

This gets more and more confusing. My poor brain needs a vacation. :p
 
perplexed said:
So secondary combustion is ONLY happening when flames are shooting out of the tubes???
Click to expand...
I didn't say that; I said if you can't see flames there is no secondary combustion. You know it is secondary combustion because either not connected to the wood or it extends the primary flames. It doesn't have to be at the air tubes but if the gasification is strong that is where it will be.
 
I finally had some secondary combustion last night. It may have been the Oak split -- I'm not sure -- but I had the temp up to 700 degrees, let a few new splits char and backed the air down 2/3 and then all the way closed. After a few minutes I had flames floating around the firebox not really connected to anything and quite a bit of floating flames at the top rear of the fire box. Nothing really shooting out of the tubes, not sure what I need to do to achieve that but this is a step in the right direction.

Question:

When running the stove as mentioned above I assume temp will slowly start to drop as the air is closed. Once the secondaries are engaged what do I wait and watch for the flames to slowly die and then open up the air? Does that signify the end of the secondary burn cycle for that load?

Thanks to all those who helped me out with this.
 
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