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Wood stove hack-secondary burn tubes added

corrupt

corrupt

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What would make a better baffle out of the 2 for secondary burn, 8mm steel plate or 1" thick fire brick? I have the steel plate now, but also have spare 9"x4.5"x1" fire bricks that I could make into a baffle if it would be worth while.
 
Misfit138

Misfit138

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What would make a better baffle out of the 2 for secondary burn, 8mm steel plate or 1" thick fire brick? I have the steel plate now, but also have spare 9"x4.5"x1" fire bricks that I could make into a baffle if it would be worth while.
The 8mm plate should be placed at the top of the firebox and have fire brick placed atop it. In this manner, the fire brick will act as an insulator, keeping the intense heat inside the firebox, and the steel plate will become superheated. There is a product called rockwool which will work even better than the firebrick above the plate.
When the unburnt gases rise and come into contact with the superheated plate, they will ignite (in the presence of sufficient oxygen).
Channeling superheated air up to the plate will enhance the effect.
This can be done (as shown in this thread) with drilled out black pipe.
The total length of the pipes should be long; about 4 feet or more if possible. In this manner, the air (more accurately, the ocygen in the air) will be sufficiently heated to aid in secondary combustion.
Happy stove building.
;)
 
corrupt

corrupt

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Thanks misfit I have still been playing, although its getting cold now so it will have to come back inside shortly. This is what I have come up with. The channel is 25mmx50mmx3mm steel and the tubes are 20mm stainless and a full fire brick lining. The screws in the back tube are from me trying to block them up to try and get slower air movement as the standard pre heat intakes are only 4 inches long and on the out side of the fire box, they will come out.

The stainless tubes hold the 1" fire brick up, do you think that is enough??

 
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corrupt

corrupt

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Thanks misfit, yep I have used it about 6 times so far.
Once it has been running for about an hour and all the bricks are up to temp there is no smoke at all, alright may be a little puff now and then but you have to be looking to see it and only when the clouds are very dark or the sky is blue (I will be in and out of the house about 10 times at different stages checking, the misses thinks im strange).
The best thing is when it dies down a bit and I chuck a fresh log on there and with out adjusting the air supply the whole box is a slow moving ball of flames, its really nice to watch. I like watching it at the very start when the wood first start gassing and you see a little smoke build up then it flashes off is a large flat flame up against the baffle.
I dont get the blue flames out of the secondary pipes like some get but it seems to be doing the job.

Shane
 
Misfit138

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Terrific.
If you really want to get crazy, you can cut down on smoke with a few tricks.
First, when cold-loading the stove, I find that a north-south log orientation facilitates a more efficient, clean burn. This has been the case on every stove I have tried it with. Place the larger logs on the bottom, reducing the size with each level, until the very top level contains only kindling. I light off the kindling with a MAPP gas torch (to my knowledge MAPP gas is no longer available, however there is an alternative product called MAPP-Pro available when this cylinder runs out). I could also lug my acetylene tank up from the cellar, I suppose..
Most people I know are surprised when I tell them that I cold-load in this way, and doubly so when I tell them I fire my stove from the top..however, it works very well and smokes less.
Next, woodstoves seem to smoke the least when you let each load burn completely down to ash and ember and then reload north-south as described above.
When hot-reloading, I remove some ash and ember about every 3rd load. I also place the largest logs on the bottom, at the left and right extremities, keeping more moderately size logs in the center. If you have a large enough firebox, you may want to experiment with just one very large log east-west in the back, and continuing with the rest north-south.
Also, in my experience, splitting the hardwoods slightly smaller than your initial intuition tells you is a big help. They will light off faster and burn nearly smoke-free.
How about some pics from the outside of the stove?
 
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BillsAutomotive

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A week or 2 ago I put a question out on this forum here:
http://www.arboristsite.com/showthread.php?t=85750
Basically, I wanted to know if replacing my stove with a more modern EPA stove would save me much wood. Since I cut my own wood and our stove is in the cellar (where it's not part of the furniture in the living room), it would be pretty hard to justify the $2500+ for a new one, and the one I've got heats the house pretty well. One of the replies was from KSWoodsMan, who said he had put secondary burn tubes in his older stove with good results. Now why didn't I think of that! So instead of cutting wood in the cold yesterday, I worked on the stove. The 1st picture below is of the tube assemblies as they were going to look in the stove. The 2nd is of the tubes mounted in the stove and the 3rd is of the outside. The tubes run up the sides of the stove. Secondary air can be controlled from the gate valves and shut off if there were ever a chimney fire. Then it enters the front of the stove over the fire, is routed through solid pipe to the rear of the stove for preheating, and then is dumped into the top of the burn area just under the baffle through the holes drilled down the length of the burn tubes. I didn't weld the tubes in place in case I ever have to change them, so I added a couple extra 1" washers so the coupling inside the stove and elbow outside the stove could be tightened against the stove wall and sealed with high temperature masonry caulk.

So far, I'm kind of impressed with my cob job. After a lot of experimenting today, I'm finding that I can get nice long hot burns by leaving the secondary valves wide open and closing the primary controls way more closed than I would normally run them. The secondary air doesn't just make the wood burn faster. In fact, it looks like I may be getting longer burns than I would normally get and put out the same or more heat. When the fire is burning at a good rate, opening up the secondaries from the closed position without changing the primary controls gets me about a 100 degree gain measured on the stovepipe. So I guess they're working. Unfortunately, since I don't have a glass door I can't see them working like you guys with the new stoves can :) So if my stove burns a little cleaner and I burn a little less for the same heat, I'll have it made.

So now for the disclaimer. I'm not recommending anyone try this on their own stove. If you try this on your old stove and trash the stove or burn your house down, I don't want to hear about it :) If you do try it and it works, or you improve on my design, let me know so we can compare notes.
very nice ,I need to chat with you
 

FJH

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Well i bought a used pac energy pre after burn for 300 bucks and made an after burn baffle plate for it, it works well also ,I also made the secondary burn adjustable ,I have also found there was no need for the secondary adjustment, other than in the event of a chimney fire a 1 inch by 2 tube feed directly into the plate would have worked just fine with out a control,I regulate the stove with the origanal draft control and leave the air wide open into the baffle and it still will have coals in the morning if i load before bed 8 to 10 hours it is the midsized stove spectrum i beleive You still need to be able to shut it down in case of a chimney fire but you could plug the holes with a rag or anything for that mater as long as the tubes are accesable and away from the heat!
 
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FJH

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Need rig sesmith !
I'm not going to go any further with my install I have tampered quite enough with the stove I am quite happy with the results of the baffel plate and the stove looks somwhat stock for insurance purposes! Also not really interested in baby sitting worring when or when not to engage the Cat!And I do like to burn news paper and paper trash from time to time .If I were the only one operating that would be fine.
 
maulionc

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Misfit138

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The efficiency of the secondary burn tubes may likely be enhanced by adding rock wool (ceramic fiber blanket) insulation to that plate just above the burn tubes.
 
wood burner man

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Is a baffle plate or fire brick needed above the tubes?

To SESMITH or all others:

This morning I came up with the ingenious idea of adding secondary burn tubes to my WoodChuck wood furnace via the ash pan door below. Hence, only 1 big hole in the middle of the ash pan door would feed air to the tubes. This would be the least intrusive surgical approach. And if it didn't work, I would not have 2 holes at the top of the burning chamber to cover up...like you have!

Then, I found out it was an old idea already invented by someone else. It is like joining the military to fight a war, but then learning the war is over.

Well, here is my question:

--I assume a separate baffle plate (or better yet, a layer of fire bricks) at the roof of the burning chamber is necessary to protect the wood stove from overheating due to the 1000 degree heat generated by the secondary burn, and to promote "light off" of the secondary burn?

My WoodChuck can burn either coal or wood, and does not have an existing ceiling baffle plate, and the fire brick only goes half way up the inside burning chamber. Hence, it is not well protected from high burning temperatures inside the fire box. It does have a big secondary heat exchanger tube on top of the burning chamber with a sliding baffle plate on each end, via a hand operated rod over the fire door.

I observed others had fire brick on the ceiling of the fire box, when they added the secondary burn tubes.

Can I assume my stove is not a good candidate for adding the tubes? My operating manual does not list any internal burning temperature maximum. The manufacturer also does not provide for adding a catalytic converter for my unit. I am not excited about a $2XX catalytic converter, since they plug up in 2-4 years and must be replaced.

I am mostly concerned about reducing the smoke from the unit, and to a lesser extent reducing wood consumption and gaining efficiency. We don't go through much wood for our home (about 3 cords (+/-) per season), but our neighborhood is getting more populated and I am concerned about complaints about wood smoke from neighbors.
 
doug4k

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woodchuck mod

i have been considering this mod for my old restored woodchuck that i use in the garage. found this forum and have been researching this mod for awhile. its great to see a completed project that looked so clean. the woodchuck has a huge firebox and with a little welding i think i could add some brackets to install a brick lined secondary chamber similar to a clayton i saw at tsc. dont know if its neccessary. would like to try the pipes only method first and see how hot it gets. i had to weld up some water pipe holes when i restored this unit. they would have been real handy at this point. keep us posted if you do anything to your woodchuck. i doubt ill be able to get to mine this winter.
 

FJH

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Adding air to the top of the fire in my opinion will enhance the burn reguardless of the presence of the insulated baffle!
The insulation will make it more efficent is all!
 
DiskDoctor

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Holes?

Nice work!
I have read and reread this thread with great interest. I found it from a web search, never thought to look here
;-)

Can you tell me the size and spacing of the holes you drilled? Fabbing is not a problem, but I wasn't sure about what to do.

Thank you for your ingenuity and willingness to share your findings and great work!
 
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