Primary Air Igniting Gasses....this happen to you?

[Woodcutter Tom]

This is for users with secondary burn tube stoves.

On my stove, I do not seem to get the secondary burn that I would expect from the secondary air which comes out of the secondary burn tubes. I also do not get the heat that I would expect transferred to the stove top and then into my living space. The highest I have ever had my stove top is 560 F. This has occurred on refills with some heat already in the stove top, but rarely.

There are times when the primary air that flows downward over the door glass ignites the unburned gasses in my stove. When this happens, the front of the stove looks like the 'gates of hell'. But the secondary burn tubes are not fully creating flames. This happens gradually when I have the primary air fully shut down. The air coming out of the secondary burn tubes is not igniting all the unburned gasses. The gasses start to be ignited by the air from the primary air flow. These become bigger and bigger flames. I can see the gasses be ignited as the air flows down over the face of the glass. It looks quite pretty. The flames dip down and then are sucked back upward. Soon this turns into the gassy 'gates of hell'. But looking back into the stove, the air from secondary tubes is just igniting gasses from the ends of the tubes. There are no flames at the center of the tubes. The heat measured by my 2 inch probe in the stove pipe increases. With the current set up it has reached 1000- 1040 F. Another results of this is that the door glass becomes dirty at the bottom. I think this would be expected as the hot clean air is not getting to the lower section of the glass. It ignites the gasses before getting that far.

Does this happen to any else here? I would expect the hot air from the secondary burn tubes to ignite all the gasses. This keeps the heat inside the firebox and slows the rush of air out the flue. To me, slower moving air results in more heat transfer to the stove top, and into my living space.


This is my understanding how an EPA stove with secondary burn tubes should work. The chimney is the engine of the stove. As the air inside the chimney gets hot it 'pulls' air from the firebox up above the baffle plate and into the chimney. As that air moves by the stove top, it transfers heat to the stove top. If the air moves too fast out the firebox and over the baffle plate it does not have time to heat the stove top plate. This is what is referred to as 'sending all the heat up the chimney'. The air has two places to enter the firebox 1.) the primary air network of square tube channels and 2.) the secondary network of square tube channels. On my stove there is a control level for the primary air; the air enters under the front of the stove inside the pedestal. The secondary air has no control; it enters through an opening at the center of the stove inside the pedestal. Air flow will take the past of least resistance. When the primary air control is wide open, that opening is the path of least resistance. Air will flow into those channels and enter the firebox as hot air above the door glass. The hot air is directed downward which moves the air over the door glass. This is the air wash that keeps the glass clean. As the primary air is shut, the path of least resistance transfers to the secondary system. The air is drawn into the firebox through the secondary burn tubes. This air has been heated as it passed through the secondary air channels. When it enters the firebox it should ignite unburned gasses. The more the primary air is shutdown, the greater the 'pull' on the air through the secondary tubes. The greater the 'pull', the more air through the tubes, and the more secondary burning of the gasses.
My primary air control does not allow the air to be completely shut down. As the control level moves toward the end of it's travel to shut down the air, the air intake actually opens. The plate that covers the intake has a hole that moves over the intake, preventing it from being fully closed. My thought is that this is for air required for the air wash system.


My current set up is 12 foot of straight 6 inch flue above the stove top to the chimney cap. The stove pipe is a double wall telescoping section. I have changed my flue length multiple times. 15' to 17' to 15' to 12' to 14' back to 12'. I am always looking for ways to get heat.

 

[NaturalCauses]

Sounds like you might have a leaky door gasket. Have you tried the dollar bill test to see if it's tight enough?

 

[Sailrmike]

This is for users with secondary burn tube stoves.

On my stove, I do not seem to get the secondary burn that I would expect from the secondary air which comes out of the secondary burn tubes. I also do not get the heat that I would expect transferred to the stove top and then into my living space. The highest I have ever had my stove top is 560 F. This has occurred on refills with some heat already in the stove top, but rarely.

There are times when the primary air that flows downward over the door glass ignites the unburned gasses in my stove. When this happens, the front of the stove looks like the 'gates of hell'. But the secondary burn tubes are not fully creating flames. This happens gradually when I have the primary air fully shut down. The air coming out of the secondary burn tubes is not igniting all the unburned gasses. The gasses start to be ignited by the air from the primary air flow. These become bigger and bigger flames. I can see the gasses be ignited as the air flows down over the face of the glass. It looks quite pretty. The flames dip down and then are sucked back upward. Soon this turns into the gassy 'gates of hell'. But looking back into the stove, the air from secondary tubes is just igniting gasses from the ends of the tubes. There are no flames at the center of the tubes. The heat measured by my 2 inch probe in the stove pipe increases. With the current set up it has reached 1000- 1040 F. Another results of this is that the door glass becomes dirty at the bottom. I think this would be expected as the hot clean air is not getting to the lower section of the glass. It ignites the gasses before getting that far.

Does this happen to any else here? I would expect the hot air from the secondary burn tubes to ignite all the gasses. This keeps the heat inside the firebox and slows the rush of air out the flue. To me, slower moving air results in more heat transfer to the stove top, and into my living space.


This is my understanding how an EPA stove with secondary burn tubes should work. The chimney is the engine of the stove. As the air inside the chimney gets hot it 'pulls' air from the firebox up above the baffle plate and into the chimney. As that air moves by the stove top, it transfers heat to the stove top. If the air moves too fast out the firebox and over the baffle plate it does not have time to heat the stove top plate. This is what is referred to as 'sending all the heat up the chimney'. The air has two places to enter the firebox 1.) the primary air network of square tube channels and 2.) the secondary network of square tube channels. On my stove there is a control level for the primary air; the air enters under the front of the stove inside the pedestal. The secondary air has no control; it enters through an opening at the center of the stove inside the pedestal. Air flow will take the past of least resistance. When the primary air control is wide open, that opening is the path of least resistance. Air will flow into those channels and enter the firebox as hot air above the door glass. The hot air is directed downward which moves the air over the door glass. This is the air wash that keeps the glass clean. As the primary air is shut, the path of least resistance transfers to the secondary system. The air is drawn into the firebox through the secondary burn tubes. This air has been heated as it passed through the secondary air channels. When it enters the firebox it should ignite unburned gasses. The more the primary air is shutdown, the greater the 'pull' on the air through the secondary tubes. The greater the 'pull', the more air through the tubes, and the more secondary burning of the gasses.
My primary air control does not allow the air to be completely shut down. As the control level moves toward the end of it's travel to shut down the air, the air intake actually opens. The plate that covers the intake has a hole that moves over the intake, preventing it from being fully closed. My thought is that this is for air required for the air wash system.


My current set up is 12 foot of straight 6 inch flue above the stove top to the chimney cap. The stove pipe is a double wall telescoping section. I have changed my flue length multiple times. 15' to 17' to 15' to 12' to 14' back to 12'. I am always looking for ways to get heat.

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I get fires exactly as you describe- tubes burning on the ends only, beutiful rolling flames against the glass. It's usually for 1/2hr- 1hr, then she settles. You mist have very dry wood! I also recommend checking your door gasket seal, my stove was new in November, and I've tightened the latch a total of two turns

 

[Woodcutter Tom]

Sounds like you might have a leaky door gasket. Have you tried the dollar bill test to see if it's tight enough?

I tested a few weeks ago. I can do it again when the stove cools down. I use a dollar bill split lengthwise in half. A full bill seems too wide for me. I think it can 'grab' and be tight when in reality there is a section of the door seal that can be leaky.

Please explain why you think it might be the door seal. What is leading you in that direction? I am always trying to learn more.

 

[Woodcutter Tom]

I get fires exactly as you describe- tubes burning on the ends only, beutiful rolling flames against the glass. It's usually for 1/2hr- 1hr, then she settles. You mist have very dry wood! I also recommend checking your door gasket seal, my stove was new in November, and I've tightened the latch a total of two turns

Mine was also new in November. I have not adjusted the door. Did you make any adjustment to the hinge side of the door? On mine there are off-set hinge pins that allow that side to be adjusted also.
I'll recheck the door seal when the stove is warm.

 

[Sailrmike]

Mine was also new in November. I have not adjusted the door. Did you make any adjustment to the hinge side of the door? On mine there are off-set hinge pins that allow that side to be adjusted also.
I'll recheck the door seal when the stove is warm.

No, I didn't adjust my hinge side, need to check my manual, don't think my model has those pins, I had seen the Deco II has them. Thanks for heads up

I have noticed my door latch is looser and moves more freely when stove is at operating temp. At room temp, it's much more snug. I made my second adjustment after noticing this, so the latch would be more snug at operating temp. Hope this helps

 

[bholler]

Mine was also new in November. I have not adjusted the door. Did you make any adjustment to the hinge side of the door? On mine there are off-set hinge pins that allow that side to be adjusted also.
I'll recheck the door seal when the stove is warm.

What stove? What is the chimney setup? What moisture content is the wood at?

 

[Woodcutter Tom]

No, I didn't adjust my hinge side, need to check my manual, don't think my model has those pins, I had seen the Deco II has them. Thanks for heads up

I have noticed my door latch is looser and moves more freely when stove is at operating temp. At room temp, it's much more snug. I made my second adjustment after noticing this, so the latch would be more snug at operating temp. Hope this helps

Just like the 'three holes' the pins are not even mentioned in my manual. Don't see them in yours either. Even on the parts breakdown.

Here is a link to my experience with them: https://www.hearth.com/talk/threads...-broken-drolet-hinge-pin.184653/#post-2478708

 

[Woodcutter Tom]

What stove? What is the chimney setup? What moisture content is the wood at?

DROLET Escape 1500
My current set up is 12 foot of straight 6 inch flue above the stove top to the chimney cap. The stove pipe is a double wall telescoping section. I have changed my flue length multiple times. 15' to 17' to 15' to 12' to 14' back to 12'. I am always looking for ways to get heat.
I have a General and also a SBI brand meter. My wood is walnut (10 - 12 % MC), Hickory (13 - 15 % MC) and Ash (13 - 15 % MC).

 

[nortcan]

Not in the obligation to use a dollar bill, just cut a piece of paper the size you need to. And you wont have your bill dirty LOL.

 

[Sailrmike]

Just like the 'three holes' the pins are not even mentioned in my manual. Don't see them in yours either. Even on the parts breakdown.

Here is a link to my experience with them: https://www.hearth.com/talk/threads...-broken-drolet-hinge-pin.184653/#post-2478708

Excellent, many thanks. I have the set screws, stove is almost cold so I'm going to pop the door off this evening and investigate my pin situation. The engineering that is put into theses stoves is really quite intense, I find them to be an incredible value (esp. In our $$)

 

[ABMax24]

Air flow will take the past of least resistance. When the primary air control is wide open, that opening is the path of least resistance. Air will flow into those channels and enter the firebox as hot air above the door glass. The hot air is directed downward which moves the air over the door glass. This is the air wash that keeps the glass clean. As the primary air is shut, the path of least resistance transfers to the secondary system. The air is drawn into the firebox through the secondary burn tubes. This air has been heated as it passed through the secondary air channels. When it enters the firebox it should ignite unburned gasses. The more the primary air is shutdown, the greater the 'pull' on the air through the secondary tubes. The greater the 'pull', the more air through the tubes, and the more secondary burning of the gasses.

This is not quite accurate. The 6" chimney will flow more air than the primary and secondary controls can supply, even if the primary is full open. Meaning the damper is the restriction on the primary side, and (if your stove is the same as mine) the holes in the secondary tubes are the restriction in that system. The amount of air flowing through the secondary tubes is solely dependent on draft, at startup under low draft secondary air volume is small, once the chimney is hot and draft is strong the secondary tubes supply a lot more air. The primary control only effects this by changing the rate of wood burn in the firebox, which in turn changes the flue temperature.

My primary air control does not allow the air to be completely shut down. As the control level moves toward the end of it's travel to shut down the air, the air intake actually opens. The plate that covers the intake has a hole that moves over the intake, preventing it from being fully closed. My thought is that this is for air required for the air wash system.

That hole is supposed to allow enough airflow to the stove to keep the fire burning, and prevent the fire from smouldering and emitting excessive smoke. Yes it does help with the airwash, but that is not the primary function.

Please see my notes in red first:

Looking at your photo I believe you have more than sufficient air for secondary combustion, and can even see where the air is entering through the flames on the edges. I believe you don't see flames at the tubes in the center because that non-burning "bubble" (for lack of a better term) is cool secondary air that either contains too little wood gas to combust, is too cool to burn, or a combination of the 2. I'd trying turning the damper down a little though, it may be a case of too much primary air for the fuel in the stove.

 

[bholler]

DROLET Escape 1500
My current set up is 12 foot of straight 6 inch flue above the stove top to the chimney cap. The stove pipe is a double wall telescoping section. I have changed my flue length multiple times. 15' to 17' to 15' to 12' to 14' back to 12'. I am always looking for ways to get heat.
I have a General and also a SBI brand meter. My wood is walnut (10 - 12 % MC), Hickory (13 - 15 % MC) and Ash (13 - 15 % MC).

How are you testing the MC?

 

[Woodcutter Tom]

How are you testing the MC?

I warm the wood inside - overnight or for a few days; split it and then measure it on the split face. The wood I burn this year is either in my garage or in an enclosed shed. Nothing comes from outside racks.
The diameter of my splits is small. My stove last year was 1.2 cubic foot. I split my wood small for that stove. If you look at Begreen's 'Starting a Fire' thread, you will see he has 10 splits in his 3.0 cubic foot stove on at N-S start up. Look at my attached picture. This is my Escape 1500, a 1.9 cubic foot stove. Typically there are about 30 pieces. Next year I will have the same size splits. The following year I may have some larger pieces that I split in 2020.

 

[Woodcutter Tom]

Please see my notes in red first:

Looking at your photo I believe you have more than sufficient air for secondary combustion, and can even see where the air is entering through the flames on the edges. I believe you don't see flames at the tubes in the center because that non-burning "bubble" (for lack of a better term) is cool secondary air that either contains too little wood gas to combust, is too cool to burn, or a combination of the 2. I'd trying turning the damper down a little though, it may be a case of too much primary air for the fuel in the stove.

Regarding your comments in red.....I understand that a 6" pipe has more volume than the area where air enters the stove. If I am reading this right, it seems like you state that the primary air and secondary air systems are totally independent and have no effect (relationship) to each other. Considering what you are stating, please answer this: Why does the burning (and flames) of gasses from the secondary burn tubes increase as soon as the primary air is decreased? To me then answer is 'path of least resistance'.


By the way, I do not have a damper in the stove pipe. As I mentioned I used different stove-top to top-of-chimney combinations to create different draft scenarios.

 

[ABMax24]

Regarding your comments in red.....I understand that a 6" pipe has more volume than the area where air enters the stove. If I am reading this right, it seems like you state that the primary air and secondary air systems are totally independent and have no effect (relationship) to each other. Considering what you are stating, please answer this: Why does the burning (and flames) of gasses from the secondary burn tubes increase as soon as the primary air is decreased? To me then answer is 'path of least resistance'.


By the way, I do not have a damper in the stove pipe. As I mentioned I used different stove-top to top-of-chimney combinations to create different draft scenarios.

By damper I mean the primary air control.

The flames increase at the secondary tubes when the primary is turned down because those gases are no longer being burnt by the air from the primary system and travel up toward the secondary tubes to be consumed.

The reason I bring up the 6" chimney is because for practical purposes it is too large to be the choke point for airflow through the stove. In your stove there are 2 entry points for air, the primary system and the secondary system. Each system has a choke point, the primary system is the primary air control, which has an adjustable area, and the secondary system is the holes of the secondary tubes, and is fixed in area. Both the primary air control area at full open and the secondary tube holes have a combined area much smaller than that of the 6" flue. I'd be surprised if this combined area is 25% that of the flue, it's likely much smaller.

When the primary air control is closed its area is reduced, reducing flow. But since the vacuum within the stove remains much the same regardless of primary air control setting the secondary tubes will still deliver the same amount of air. The secondary tubes are just a series of orfices, and the only variables in a simple orfice are differential pressure (vacuum) and area, and if neither of these variables are changed then the volume of air flowing through them doesn't either.

Now there are caveats to this, turbulence in the firebox can affect the perceived differential pressure the secondary tubes see to some extent. Also at high primary air settings friction losses in the stove pipe will result in a small reduction in differential pressure seen at the stove, but this is often more than made up for by higher flue temps.

I've wrestled with this concept as well in my own Osburn model, but under certain conditions (an extremely hot fire with dry wood) you can see that even at high primary air settings the secondary system is delivering air to the firebox. After exploring this I'm not sure I agree with SBI's (parent company of Drolet, Osburn and others) design for these firebox's. The primary control in many ways also turns into a mixture control, I know there are many times at low settings when I'm blowing carbon monoxide and unburnt wood gases out the flue because the secondary system is delivering far too much air making the mixture too cool and too lean to ignite. I'm now a big believer in having some kind of variable control over the secondary air, much like the old Pacific Energy stoves used to use with a rod to control a damper over the secondary inlet that moved in conjunction with the primary control.

 

[Sailrmike]

By damper I mean the primary air control.

The flames increase at the secondary tubes when the primary is turned down because those gases are no longer being burnt by the air from the primary system and travel up toward the secondary tubes to be consumed.

The reason I bring up the 6" chimney is because for practical purposes it is too large to be the choke point for airflow through the stove. In your stove there are 2 entry points for air, the primary system and the secondary system. Each system has a choke point, the primary system is the primary air control, which has an adjustable area, and the secondary system is the holes of the secondary tubes, and is fixed in area. Both the primary air control area at full open and the secondary tube holes have a combined area much smaller than that of the 6" flue. I'd be surprised if this combined area is 25% that of the flue, it's likely much smaller.

When the primary air control is closed its area is reduced, reducing flow. But since the vacuum within the stove remains much the same regardless of primary air control setting the secondary tubes will still deliver the same amount of air. The secondary tubes are just a series of orfices, and the only variables in a simple orfice are differential pressure (vacuum) and area, and if neither of these variables are changed then the volume of air flowing through them doesn't either.

Now there are caveats to this, turbulence in the firebox can affect the perceived differential pressure the secondary tubes see to some extent. Also at high primary air settings friction losses in the stove pipe will result in a small reduction in differential pressure seen at the stove, but this is often more than made up for by higher flue temps.

I've wrestled with this concept as well in my own Osburn model, but under certain conditions (an extremely hot fire with dry wood) you can see that even at high primary air settings the secondary system is delivering air to the firebox. After exploring this I'm not sure I agree with SBI's (parent company of Drolet, Osburn and others) design for these firebox's. The primary control in many ways also turns into a mixture control, I know there are many times at low settings when I'm blowing carbon monoxide and unburnt wood gases out the flue because the secondary system is delivering far too much air making the mixture too cool and too lean to ignite. I'm now a big believer in having some kind of variable control over the secondary air, much like the old Pacific Energy stoves used to use with a rod to control a damper over the secondary inlet that moved in conjunction with the primary control.

Idk, I'm pretty happy with simplicity of one lever. Adding secondary control would make them too draft sensitive. Compared to a lot of inexpensive stoves, the sbi box has a lot of controllability and very clean burning.

 

[ABMax24]

Idk, I'm pretty happy with simplicity of one lever. Adding secondary control would make them too draft sensitive. Compared to a lot of inexpensive stoves, the sbi box has a lot of controllability and very clean burning.

I'm not saying add a second lever, the EPA would never go for it. It would have to be tied in with the primary control. I think it would make the stove less draft sensitive if both were controlled at the same time. I've wrestled with overdraft with my stove since day 1.

 

[Sailrmike]

I think smuch has to do with variation in m.c.
This is relatively more wet wood than I've been burning lately . Much less active primary, better secondary. Op has really dry wood split small, primary fire takes care of most of the combustion, secondaries are less needed. Just my theory lol

 

[Woodcutter Tom]

I tested the door seal this morning. It passed the dollar bill test all the way around.

Sailrmike and ABMax24, do you get the heat from the stove that you expect to get ?? The highest I have ever had my STT is 560 F. Normally I can get to 450 ish pretty regularly but that temp does not heat the room and spread it to other areas very well.

My goal is Heat. That is all I really what I want out of my stove. I'm trying figure out how to get it.

Today is suppose to be very wind 25 - 35 mph, so any testing today will be suspect.

But since the vacuum within the stove remains much the same regardless of primary air control setting the secondary tubes will still deliver the same amount of air.

This is the sentence that makes me scratch my head. My thought pattern leads me to believe that the vacuum would increase as the primary air is reduced. And thus more air would be pulled from the secondary tubes into the vacuum. Time to go back to Physics class. I should have been paying attention instead of looking at the pretty blond girl two desks over.

My stove has four secondary burn tubes; each with 28 holes. Would a reduction in the number of holes slow the air flow and thus increase secondary burn?

 

[Sailrmike]

I tested the door seal this morning. It passed the dollar bill test all the way around.

Sailrmike and ABMax24, do you get the heat from the stove that you expect to get ?? The highest I have ever had my STT is 560 F. Normally I can get to 450 ish pretty regularly but that temp does not heat the room and spread it to other areas very well.

My goal is Heat. That is all I really what I want out of my stove. I'm trying figure out how to get it.

Today is suppose to be very wind 25 - 35 mph, so any testing today will be suspect.


This is the sentence that makes me scratch my head. My thought pattern leads me to believe that the vacuum would increase as the primary air is reduced. And thus more air would be pulled from the secondary tubes into the vacuum. Time to go back to Physics class. I should have been paying attention instead of looking at the pretty blond girl two desks over.

My stove has four secondary burn tubes; each with 28 holes. Would a reduction in the number of holes slow the air flow and thus increase secondary burn?

I get plenty of heat, more than I expected. I've had my stovetop to 600° measured by magnet therm in front of the heat exchanger. These stoves do have a c-cast panel attached to underside of stovetop, I imagine that this keeps temps a little lower. When I measure stovetop temp with my i.r gyn, I can easily get 50-100° hotter near the flue collar

 

[ole]

I think your stove would like bigger splits. My Escape 1800 I can stovetop 700F easy with splits much bigger than your pic.

 

[ABMax24]

Sailrmike and ABMax24, do you get the heat from the stove that you expect to get ?? The highest I have ever had my STT is 560 F. Normally I can get to 450 ish pretty regularly but that temp does not heat the room and spread it to other areas very well.

Yes I get heat that I expect, mine is bigger than yours though, yours is 1.9cuft mine is 2.4cuft. But the design of both fireboxes are nearly the same, proportions just change. I've never checked stove top temps on mine, mine has a steel/soapstone top that makes checking this cumbersome. That being said I have seen the center of the stove top glow a very faint red in a pitch black room, which should be somewhere around 750F, so it gets hot.

I would try different wood loadings, using lots of small splits in a bottom up start, this should get the stove hot. If it doesn't I'd be concerned you have too little draft. Also try opening a window a crack when running the stove, maybe the house is too well sealed to allow proper draft and the window open would alleviate this. The one thing that has me puzzled is your flue temps, if you can hit 1000F in the flue you should easily hit 700F on the stove top. In my above scenario where my stove top was glowing, my flue temp reading was 675F. But I am curious about the C-Cast panel under the stove top that @Sailrmike is referring to, mine definitely doesn't have this, and could reduce stove top temps considerably.

 

[Woodcutter Tom]

These stoves do have a c-cast panel attached to underside of stovetop,

What is a c-cast panel? I never heard of that term. My stove appears to just have the 5/16" stovetop....but one of the diagrams in the manual shows a dark line attached to the underside of the stovetop. That could be it. I'll have to look closer when the tubes and baffle board can be removed.

I think your stove would like bigger splits. My Escape 1800 I can stovetop 700F easy with splits much bigger than your pic.

After I got this stove, I started to split my wood into larger pieces. I have oak, ash and hickory. That won't be seasoned for some time yet. Next years wood is already split....into the smaller pieces. I am going to try to kiln dry some of the larger splits in an attempt to have them ready for next year.

Yes I get heat that I expect, mine is bigger than yours though, yours is 1.9cuft mine is 2.4cuft. But the design of both fireboxes are nearly the same, proportions just change. I've never checked stove top temps on mine, mine has a steel/soapstone top that makes checking this cumbersome. That being said I have seen the center of the stove top glow a very faint red in a pitch black room, which should be somewhere around 750F, so it gets hot.

I would try different wood loadings, using lots of small splits in a bottom up start, this should get the stove hot. If it doesn't I'd be concerned you have too little draft. Also try opening a window a crack when running the stove, maybe the house is too well sealed to allow proper draft and the window open would alleviate this. The one thing that has me puzzled is your flue temps, if you can hit 1000F in the flue you should easily hit 700F on the stove top. In my above scenario where my stove top was glowing, my flue temp reading was 675F. But I am curious about the C-Cast panel under the stove top that @Sailrmike is referring to, mine definitely doesn't have this, and could reduce stove top temps considerably.

I believe that I have good draft. I have an OAK. It is a 5" diameter tube that SBI calls for in their specs. I can feel (and hear) the air entering the end of the tube. My primary air control is very sensitive. Small increments effect the flame in the firebox. I can see the movement of the flames when making adjustments to the primary air control --- The air rushing in and pushing the flames around. That makes me believe that I have good draft. Plus I have tried every combination of chimney height that I can.
If I want, I can create a massive inferno in the firebox. But the heat seems to go out the flue. My highest flue temp was over 1200F when I used some pressed sawdust blocks. I used 5 with a couple of stringers underneath them. The blocks took a while to get going, but when the stringers ignited the blocks soon followed. Big inferno. But the heat did not transfer into the stove top. It went up and out the flue.
It puzzles me that you have STT greater than or equal to the flue temp. I also see that in @begreen's fire staring tutorial where his stove is cruising at 613F Flue and 625F SST.

I am hoping to hear back from SBI soon. I replied earlier this week to some questions they ask me. Hopefully thay can shed some light o this. (but I'll settle for heat, not light)

 

[Woodcutter Tom]

I would try different wood loadings, using lots of small splits in a bottom up start, this should get the stove hot. If it doesn't I'd be concerned you have too little draft.

I'm going to try this: I'll let the stove cool down, sweep out all the ashes and load up new. I'll shut a gate valve I have on the air intake about 1/2 way. Try to slow the draft. Let the air linger longer in the secondary tubes.

Looking at your photo I believe you have more than sufficient air for secondary combustion, and can even see where the air is entering through the flames on the edges. I believe you don't see flames at the tubes in the center because that non-burning "bubble" (for lack of a better term) is cool secondary air that either contains too little wood gas to combust, is too cool to burn, or a combination of the 2. I'd trying turning the damper down a little though, it may be a case of too much primary air for the fuel in the stove.

In that picture the primary air was closed all the way. If the secondary air is too cool, this may heat it up a bit more.