# secondary burn tubes



## BAllen83 (Jan 13, 2014)

I have an older sierra rear venting wood stove and was interested in putting secondary burn tubes in it. Has anyone ever done this or can it not be done on a rear venting stove? Looking at building my own if its possible.


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## Huntindog1 (Jan 13, 2014)

Would be cheaper to buy you an entry level stove thats already has the tubes and it would be brand new.

What part of the USA are you in?


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## BAllen83 (Jan 13, 2014)

I live in central Ohio. We really like this stove mainly for the reaon it is the perfect size for our hearth just would like to get longer burn times out of it. Any bigger of a stove wouldn't fit and would probably be over kill as this stove heats the house great. Do you think it would be to expensive to do this or unsafe or just simply to big of a project?


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## Huntindog1 (Jan 13, 2014)

It would not perform like a stove designed from the ground up to do secondary burn.


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## Huntindog1 (Jan 13, 2014)

What size stove is it and how big is your house . How big hearth do you have?


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## BAllen83 (Jan 13, 2014)

Outside measurements of stove are 28"H x 26"L x 18"W. House is right at about 2,000 square feet.


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## Huntindog1 (Jan 13, 2014)

Do you have room to install a top vent stove. In your avatar looks like your opening is taller than the stove you have.


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## BAllen83 (Jan 13, 2014)

Yes I do have the room..but like I said I would like to keep the same stove. I have seen other posts where guys have done this but they were all top venting stoves.


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## BAllen83 (Jan 13, 2014)

Here is the thread i was reading about a guy that made is own on an older fisher stove https://www.hearth.com/talk/threads...ma-bear-or-grandpa-bear-more-efficient.15589/


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## tjcole50 (Jan 13, 2014)

You should get an nc13/30 cut the legs down and partially put in fireplace opening


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## BAllen83 (Jan 13, 2014)

I know a guy that just intalled a nc-30 and was having some problems with heat output. I can aassure you that it had nothing to do with install! Thanks for the advice tjcole50, but i would like to see if this can be done with my current stove!


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## tjcole50 (Jan 13, 2014)

Haha well fix that nc-30 and I think we can do that with you stove only issue is it's shape and is a baffle required on top of burn tubes? Also not sure if rear vent with screw with those plans or not ... Once my internet is back up ill do some research


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## BrotherBart (Jan 13, 2014)

As a twenty year Sierra burner I can tell ya that a liner, dry wood and keeping the stove burning around 500 or over is gonna do all the pup has in it. If you look up in it and see rolling blue flames up at the baffle it is doing secondary burn already.

What they called "Turbo Burn".


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## BrotherBart (Jan 13, 2014)

tjcole50 said:


> Haha well fix that nc-30 and I think we can do that with you stove only issue is it's shape and is a baffle required on top of burn tubes? Also not sure if rear vent with screw with those plans or not ... Once my internet is back up ill do some research



Once you get that 30 working, start giving advice.


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## BAllen83 (Jan 13, 2014)

Haha, thanks brother Bart. I love the stove and the heat it produces, it easily heats my hole 1 story 2,000 square foot house, I was just looking to extend burn time so i dnot have to rely on the wife so much in the evenings while I'm at work...if yout know what I mean! And tjcole.......we'll get that puppy pouring heat into that house yet!


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## tjcole50 (Jan 13, 2014)

Damn straight once we do we need a night off infront of it slammin booze


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## BrotherBart (Jan 13, 2014)

This Sierra T-4500 heated this two story 2,500 sq. foot barn for 21 years. Unfortunately this pic was taken the night after I installed a liner and with the new monster draft I discovered the crack in the firebox behind the baffle and it ran away on me. Pulled it out and replaced it a week later.

I miss that stove. Even though the replacement heats the joint better with half the wood. Just had a lot of history with Old Brownie. Two thirds shut down and with those blue flames rolling under the baffle and no smoke out of the chimney the sucker would burn forever.


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## BAllen83 (Jan 13, 2014)

Very nice set up. After I gof mine all installed with the liner and all I also have monster draft even though my chmney is only 15'. I had a busted up iinsert in when i bought the house aand it was vented directly into chimney no liner at all...luckily the house didnot burn down. Was als going thrrough 7-8 cords a sseason. Now I am down to about 1 1/2 truck loads a mnth aand house staying at 75°


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## Smoke Signals (Jan 14, 2014)

Those are great old stoves and I can understand why you want to hang on to it. Depending on you'r fabricating skills and access to a decent shop you could have a lot of fun modifying it. I think you could modify the baffle and add some secondaries to it if you wanted to but it would be a bit of work. Check out the link in my sig line to see what I did to mine. I'm still working the bugs out but I will do my best to answer any questions you may have.

P.s. as stated in your other thread, for the price and ease of installation I would go with a pipe damper


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## BAllen83 (Jan 14, 2014)

I checked out your thread on your stove mods  and all I can say is I want that! Awesome job! If there is anyway to get plans with more detail i would love to try this. Do you tthink this would work if i kept the outlet of the stove on the back?


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## Corey (Jan 14, 2014)

As a person who has actually converted a stove, I will reply with my observations to some of the above threads.  Sorry in advance, but I will respectfully disagree with some.

1) Cost.  My trip to the scrap yard for ALL steel required for the retrofit was about $40.  Substantially less than a new stove of any make/model.  If you double that for welding consumables, you're still well under $100.  Even the NC30 is probably going to be 7, 8 or 9x that much.  This assumes you have a welder, ways to cut/drill/grind metal, general skill in metalwork and fabrication.  If you're planning to go to a machine shop that could eat most, if not all of the savings.

2) Heat output.  Well, when the old configuration would run away with herself, I have seen stove top temps up to 950F which corresponds to a LOT of heat output.  With the baffle and new controls, I can still make it run away, but it's not 'accidental' anymore.  So at the extreme, I'd say heat output could be the same.

3) Burn efficiency.  I probably go through half the wood I did.  This seems to be a combination of better air controls and more efficient burning.  Every time I see any flame at all on the secondary combustor, I know that is energy which would have gone up the flue before.  The tubes are usually glowing red or orange hot and look like a full-blown gas burner with all the flames coming out, so that is a lot of recovered energy.  I can also control the burn much better to stretch 6, 8 or even 10-12 hours of usable heat out of the stove, whereas before, it was much more of a 'flash fire' 3-4 hours of heat and a quick cool down.

4) Operation.  This is a little more tricky.  Before I had the choice of air or not.  Now I can let air in under the fire, at the air wash for the glass, at the base of the fire, or into the secondary system.  In a factory system, they've done the R&D and this is all gated to work off a single lever.  In DIY, it's a little more tentative.  It's definitely something you have to learn...kind of like running the enrichment, spark advance, etc in an old model T vs just getting in a new car and going.

5) Construction.  Again, I had all the tools and equipment.  If you're planning to farm it out, double check cost first.  I used scrap stainless steel for the secondary tubes and supports.  Seems to work great and can really take the heat.  Typical red/orange operation:





I estimated an opening around 10% of the 6" flue might be good start to feed the secondaries...so around 3 square inches and I threw in about one more square inch thinking it's always easy to close the gate down, but a major pain to cut this one out and weld in a bigger one.  Turns out I seem to have the gate open only a fraction of what it could be...usually a square inch of opening or less.  I based the hole pattern and orientation off the NC-30 (p17)

http://www.homedepot.com/catalog/pdfImages/e3/e3dda524-8c99-482d-af74-764abbb59fef.pdf

If you're seriously considering the retrofit, I'd go give an NC a good lookover, take some measurements and make some notes.  Should give you a good idea of what is needed if you retrofit.

Hope this helps dispell some myths.  Overall, I'm very happy with the conversion...much more even heat output, easily controlled burning, cleaner and less wood consumption.  I've kicked around retrofitting a catalytic combustor to scrub that last bit of soot and gain a bit more efficiency.  But the $200 initial price and estimated 3 year life is a little hard to swallow!

Either way, good luck!


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## BAllen83 (Jan 14, 2014)

Thanks Cory. Gonna try and get some plans and im gonna give this a shot. Still tryin to find out if it can be done on a rear exit stove.


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## Smoke Signals (Jan 14, 2014)

First off I guess I should say that you assume all risk for any mods that you make to your stove. Take all advise that you receive on the interwebs with I big grain of salt. yada yada. Bottom line, don't burn your house down!

Now, with that out of the way, sorry no plans and looking back I would do it differently now any way. Your setup is different than mine but I think you could make it work. You would have to work around hole where the smoke exits the stove. I think that would be the biggest challenge, figuring out how to make your baffle so it doesn't inter fear with the smoke exit and so it doesn't take up too much of your fire box. Maybe you could make a frame out of tubing to preheat you secondary air and support fire brick to create your baffle. I would make my pre heater longer now that I know how it works as is.

In my stove the smoke travels to the left of the fire box, up over the brick baffle and back to the right to exit the stove, With yours, I think you would want the smoke to travel up and towards the front of the fire box, up past the baffle at then to the back where it exits. The secondaries would be under the brick baffle. I think you would want the holes in the tubes pointed towards the front of the fire box. this is my vision of how it would work, you may have a different idea and again this is all speculation on my part so take it for what its worth. One other pice of advice, make your mods bolt on so they are easy to remove if they don't work or if you need to tweak them a little. I welded some of mine to the stove and kind of wish that I hadn't now.


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## BAllen83 (Jan 14, 2014)

Copy that smoke. thanks For the advice and hints. Gonna wait until burn season is over to start this seeing how my stove is primary heat and it is mid January.


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## Smoke Signals (Jan 14, 2014)

Good Luck! Keep us posted.


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## BAllen83 (Jan 14, 2014)

Will do. thanks for all the input fellas!


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## Corey (Jan 15, 2014)

BAllen83 said:


> Thanks Cory. Gonna try and get some plans and im gonna give this a shot. Still tryin to find out if it can be done on a rear exit stove.



I suppose it 'can' be done, though you will need to leave some offset between the top baffle and the back wall where the flue is.  Whereas with a top exit, the only concern is leaving a space between the top of the stove and the top of the baffle/tubes.  Depending on how big your firebox was to begin with and if the reduction in size is acceptable.  I would say allow at least a couple inches of space in each dimension, plus figuring the back wall and top baffle may be a couple of inches thick additionally, this could mean taking 3-4 inches off each dimension.

If that makes things too small, it's not too hard to convert over to a top exit while you're cutting and welding secondaries anyway.  I actually converted from a ~3x14" rectangular hole 'slammer' to a standard 6" flue collar.


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## Smoke Signals (Jan 15, 2014)

I don't know how much top clearance you have but along the lines of what Corey is thinking with the top exit, you could remove the smoke collar you have now and close up the hole. Then weld up a box with the bottom open and a 6' round outlet coming out of the back, cut a hole it the top of the stove and weld (or bolt) this box over it so you would have a top/rear out let or a top outlet that points back. I guess that may ruin the look of the stove but it's and idea. You could also design this top outlet box in a manner that would allow for that addition of a cat and a bypass at a later date if you  decided that you needed one.


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## BAllen83 (Jan 15, 2014)

okay guys next question I work in a tubing factory and have all kinds of access two different sizes the tubes do you think a raw steel tube would be okay to use as the secondary burn tubes to be able to withstand the heat


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## Smoke Signals (Jan 15, 2014)

I'm not sure how long they would last but if the price is rite it's worth a shot in my opinion. Just make them so they are easy to change out.


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## begreen (Jan 18, 2014)

BAllen83 said:


> okay guys next question I work in a tubing factory and have all kinds of access two different sizes the tubes do you think a raw steel tube would be okay to use as the secondary burn tubes to be able to withstand the heat




Stainless will stand up to the heat better if you have access to that tubing.


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## BrotherBart (Jan 18, 2014)

Every stove maker that tried using mild steel for burn tubes has changed to 304 stainless.


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## Corey (Jan 19, 2014)

If it is thick enough, mild steel would work...at least for a moderate amount of time.  If you could get 1" sch 40 pipe, it would have a wall thickness just over 1/8 inch.  Would probably get you a couple years of use before it burns through.  The down side is, ideally you want the tubes to be thin, so they heat up fast and start burning smoke quickly.  Having the 'mass' to hold the heat isn't really a factor because the coaling stage of the fire is pretty clean anyway. 

If you can hit a scrap yard and find some thin wall stainless, it would be ideal, or even prowl around ebay.  You can usually find a 4-6ft stick of 3/4 or 1" dia tubing for under $30.  I got some sections of 2"x2"x1/8" wall square stainless to make my frame and some 1" round stainless tube to cut up into burn tubes.


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## Boil&Toil (Jan 19, 2014)

If you know how to spot it (I can show people, but I have no luck writing a text description) stainless is often cheap at a scrap yard (if they even take it.) You may also find that you can pick some up as a manufactured product, cheaper than you can buy the raw stock - tub/bathroom handicap grab bars come to mind. Generally a non-magnetic stainless will hold up better than a magnetic stainless, and if you're sourcing your material this way, that will be about all you know about the alloy in most cases (if you bring a magnet.)

I would think that using the secondary supply tubes (not the thinner burn tubes, if the burn tubes are quite thin - if they'll take the abuse of having wood dumped on them when hot, thick enough) as a grate would be a good approach to at least part of the preheat for the secondary air.


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## WES999 (Jan 19, 2014)

I used .75 x .06 wall 304 stainless tube for my Fisher conversion.
I purchased from here:
http://www.onlinemetals.com/merchant.cfm?pid=471&step=4&showunits=inches&id=19&top_cat=1
I think I got 2 4' lengths, cost about $40,  it should last almost forever.


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## valley ranch (Jan 20, 2014)

Corey good go! I think adding secondary is the way to go for guy with great old stoves. There are also some nice videos on the net, google and see what you can find. I've seen some quickie jobs and some take your time mods. The all work, some better, some great.

Richard


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## Shwammy (Sep 14, 2014)

BAllen23, I'm working on doing the same thing to my Sierra 1000 as well. Currently I'm building a firebrick baffle to replace the old worn out metal one in the stove. I think I now have devised a way of mounting it loosely but securely without welding it specifically though I do need to weld a strip across the bottom of the old baffle where I've cut it off. I figure I can test/modify/move it this way and get it's design ready first before messing with secondary burn tubes. The baffle will be 4 firebricks set in a steel angle holder and will lean toward to where the sloped top plate meets the flat top plate with about a 3 inch gap left. I plan to cap the ends with firebrick as well to even the distances up around the baffle. Also I talked to a customer at work who builds furnace parts and he's going to bring me some scrap ceramic boards they use as liners so I may just end up using that as a baffle instead of the fire bricks. I just need to test it so I know if my baffle will work the way I want it too without smoking up the house or something, then it's secondary time. Luckily I have most of the materials already. We cut some 1 1/2" stainless tubing at work last week and had about 8 pieces around 3 feet long left over. A few of those will make the manifold portion of my secondaries. For the air tubes I can get 1/2" stainless tubing all day long, we go through miles of the stuff at work and I don't need very long lengths. I probably won't get to the secondaries until after the burning season though. I like to sit on an idea for a while and see if it gels in my head. Plus it will be nice to have a comparison between before and after. I really look forward to it. This stove is of an odd design, but it sure fits right. And so far I only have about $200 in the whole thing and need to spend about $100 more for glass and some more fire bricks. I hope it's not a $300 disaster, we'll see.


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## valley ranch (Sep 16, 2014)

Greetings Shwammy, Just read your post. I can't picture it well, hope you can post pictures. I used a Sierra Benzel or frame when I put glass in the door of my stove. Good luck with the modification. Talk to you later. 

Richard


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## Shwammy (Sep 16, 2014)

The stove is a side door rear exit like in the OP's avatar. The new baffle is just an 18'' wide x 9'' tall steel angle frame with 4 firebricks laid in it instead of the old 10'' wide x 10'' tall steel baffle. It will sit up at around a 60 degree angle or so (not sure on that yet its more of an eyeballing thing). The bottom of the baffle will sitting partly against where I cut off the bottom inch of the old baffle plate so it will actually be taller  There will be bricks cut into triangles sitting on the ends filling the gap from the main part of the baffle to the back wall. This will look like an 18'' wide upside down dryer vent and cause the fire and smoke to travel a much further path as it exits and provide me room to mount secondaries down the underside of the baffles. Before it was just a rectangular box with a piece of steel mounted in it that more or less just kept the flue from being blocked off by an overzealous loader. Now it will have a baffle/smoke shelf which won't be too much of a space hog but will be effective with the rear exit...in theory. I'll take some pics when I get a chance. I'm trying to have the thing finished this weekend, minus the secondaries.


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## valley ranch (Sep 16, 2014)

Sounds great, good for you, get it done.

Richard


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