Adding secondary burn to this unique stove

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AtomicDog

Member
Aug 21, 2014
49
East TN
I have a stove that may be perfect for adding secondary burn. I was about to buy a PE Summit, but decided to look into this mod first. The stove has a blower that feeds air through a manifold of welded pipe in the top. It seems like I could weld the ends of the pipes shut and drill a bunch of holes on the inside. The way the stove is shaped should make this work if I understand the process. A lot of hot gasses are trapped in the top section. The air blows through the manifold and out of the ends of the pipes. Hopefully the picture will help. I would like to keep the stove because it can take 32in splits. This is a front view of the stove and top view of the existing manifold:
stove.JPG
 
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stoveliker

Minister of Fire
Nov 17, 2019
2,967
Long Island NY
I'd take off the blower then, have the draft suck in secondary air. Otherwise you risk blowing too much (too fast, and hence cold) air in the top.
 

AtomicDog

Member
Aug 21, 2014
49
East TN
Thanks. My plan is to replace the blower with a valve or shutter. I guess the real question is will I gain anything worthwhile with this mod?
 

stoveliker

Minister of Fire
Nov 17, 2019
2,967
Long Island NY
I don't know... Is that the only air? Was it meant for combustion air, or (b/c blower) just to heat room air to extract heat from the stove?

It won't make the stove go nuclear (x-10 or y-12... - I was at x-10 for 11 years) :)
 
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SpaceBus

Minister of Fire
Nov 18, 2018
6,444
Downeast Maine
Other folks have implemented similar designs to older stoves. It won't be a 75%+ efficient modern stove, but it will be a significant improvement over an old smoke dragon. You may also need some kind of baffle for the flue exit to slow down the gasses enough to combust with the additional preheated air from your manifold. As already mentioned, a blower is not going to be a good plan. It will probably pressurize the stove and push smoke out of the primary intake. Your idea of closing off the tubes and putting some kind of valve or slider on the old blower opening is solid. Eventually you will just leave that air control alone once you figure out where it works best and only adjust the original air control.
 

MR. GLO

Feeling the Heat
Jan 26, 2021
252
Massachusetts
Other folks have implemented similar designs to older stoves. It won't be a 75%+ efficient modern stove, but it will be a significant improvement over an old smoke dragon. You may also need some kind of baffle for the flue exit to slow down the gasses enough to combust with the additional preheated air from your manifold. As already mentioned, a blower is not going to be a good plan. It will probably pressurize the stove and push smoke out of the primary intake. Your idea of closing off the tubes and putting some kind of valve or slider on the old blower opening is solid. Eventually you will just leave that air control alone once you figure out where it works best and only adjust the original air control.
Great info did folks see longer burn times with the new baffle and tubes?

I wonder if somone could buy the pe baffle /tube and get it to work in an old stove.
 

Corey

Minister of Fire
Nov 19, 2005
2,627
Midwest
Can be done. A few things for consideration:

Ideally the secondary air would be brought in fairly low... at or below the floor of the firebox, This will help reduce the possibility of smoke / combustion gasses backing up the tubes and coming out into the room.

Secondary air would ideally be exposed to the firebox internals for a good section of the run, and if you can set up a big chamber so the air slows down and spends even longer exposed to the heat, that is even better. This helps super-heat the air. In combination with firebox heating plus heating in the burn tubes, the air can easily be over 1200ºF before jetting out the tubes. If your tubes aren't stainless, this will eventually degrade them and cause 'burnout'. But even generic thin wall stainless seems quite resistant. My tubes are 0.050" wall and see orange-hot heat each season for 15+ years with no notable degradation.

You might look up the pattern / size of holes from an NC30 as some guidance. But ideally, you're punching an 1/8" hole about every linear inch along the burn tube and at an angle where the flame from any given tube jets downward for a bit, but curves back up so the tip of that flame directly hits the burn tube in front of it. This helps magnify the secondary burn effect as each tube helps heat the tube in front of it. I ended up with 4 tubes x ~22 hole each, so depending on the size of your stove and access, that is a lot of drillin' at what seems to be less than ideal body positioning.

As far as air inlets. I was somewhat surprised on my retrofit. Air intake about the size of a quarter seems to be about right. I was prepared for a much larger inlet, but anything more just flushes too much air through, cools the tubes and kills the effect. Thought I recall seeing a couple others use either a 1" or a 3/4" ball valve. So again, in that size range. You certainly won't need a 2 or 3 inch diameter inlet.

It will also be really hard to judge how well it's working if you don't have a glass door. You obviously can't see through a steel door and the moment you open the door to check, it kills any secondary burn.

Not sure how that 'nub' on top of your stove is insulated. As mentioned, my tubes easily glow orange hot, so would likely be something you'd want to protect the surface of the firebox from.
 
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stoveliker

Minister of Fire
Nov 17, 2019
2,967
Long Island NY
@Blazzinghot also has done this a number of times, I believe.
 

Blazzinghot

Burning Hunk
Dec 5, 2019
231
New Plymouth, Idaho
It would be nice to see a picture of the stove and how it is set up. Sounds like an interesting project. Cory has made a good point about having the secondary air intake at a lower level which will also help to preheat the incoming air. I would like to see how this all plays out when it is finished. I would start with a few holes and then experiment with building fires in the stove. A person could get to much secondary air. But a control valve as mentioned would certainly help as it would be difficult to figure out the ratio or secondary air to that large of a chamber. I don't really don't know but wonder if the size of the tube makes a difference for getting a good secondary burn?
 

3650

Minister of Fire
May 8, 2011
710
midwest
I put secondary air in a stove and I used black pipe to plumb it in the length of the stove making a u turn up and back to the middle then over to the center to a stainless steel h shaped barbecue burner. It worked great!
 

stoveliker

Minister of Fire
Nov 17, 2019
2,967
Long Island NY
I like the blade :)
 

Blazzinghot

Burning Hunk
Dec 5, 2019
231
New Plymouth, Idaho
This gives me a much better perspective of what you are doing. It seems you are going to cap both ends of the blower pipes and have the secondary air come in from the location of where the fan used to be? This is much different than a usual set up and will be curious if it works? Most of the time the secondary air heats up in the lower chamber with ceramic board and insulation on top and then exits to the top chamber and out the stack. You have skipped all this and are mixing the two in the same location. To bad this stove does not have a viewing window to observe the results. Well never hurts to experiment. It seems you are moving right along with this project . Keep us posted with the results.
 

SpaceBus

Minister of Fire
Nov 18, 2018
6,444
Downeast Maine
This gives me a much better perspective of what you are doing. It seems you are going to cap both ends of the blower pipes and have the secondary air come in from the location of where the fan used to be? This is much different than a usual set up and will be curious if it works? Most of the time the secondary air heats up in the lower chamber with ceramic board and insulation on top and then exits to the top chamber and out the stack. You have skipped all this and are mixing the two in the same location. To bad this stove does not have a viewing window to observe the results. Well never hurts to experiment. It seems you are moving right along with this project . Keep us posted with the results.
If you look at the photo from inside the firebox the manifold should get plenty hot. It's almost tailor made for the application.
 
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stoveliker

Minister of Fire
Nov 17, 2019
2,967
Long Island NY
If you look at the photo from inside the firebox the manifold should get plenty hot. It's almost tailor made for the application.
I agree. Nice stove to do this with.
 

AtomicDog

Member
Aug 21, 2014
49
East TN
Head first down the rabbit hole. Based on what everyone has stated, I really need a baffle to make this work. My idea now is to cut open part of the top of the stove on the front edge, then add another chamber on top with a flue opening. This changes the top of the stove to a baffle. Maybe this drawing will help.
Capture.JPG

The grey area is the addition. The hatched area is insulation.
 

stoveliker

Minister of Fire
Nov 17, 2019
2,967
Long Island NY
How tall is your chimney? Baffles will increase impedance in your drafting.
 

AtomicDog

Member
Aug 21, 2014
49
East TN
No one has noticed the second blade behind the stove. That's a heat deflector for my cat. She flattens out like a flounder under the stove. The blade is there to cover the clean out. There's a door held in place by magnets just below the pipe. I normally have a black ring around the pipe. The flash really makes it look a lot worse than it is. My end goal is to cover that wall in some slightly rusted corrugated metal from the barn roof with the blade on top.
 

stoveliker

Minister of Fire
Nov 17, 2019
2,967
Long Island NY
Your chimney should be ok then (in length). I did notice the second blade. Did not want to comment b/c I try to avoid embarrassing people in case this was "just laying there"...
(I.e. I don't want to have people feel they need to apologize for "the mess"...)
 

Blazzinghot

Burning Hunk
Dec 5, 2019
231
New Plymouth, Idaho
AtomicDog it sounds like you have some good ideas. With the flue on the top you will force the air up and around the secondary burners more like on the modern wood stoves. How much room to you have from the tubes to the top of the stove? I was thinking about your project yesterday and was trying to figure out how you could improve it but it looks like you are heading in the right direction. Sounds like a allot of work but for me it is fun work. I am not picturing what you are saying about the cat.o_O

If you haven't already you might study some pictures of secondary burners. You can find diagrams on the internet. I was checking my pictures folder but most of my pictures are for a cat stove or a hybrid.
 
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