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Picture of Woodstove Heat Exchanger
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      I wanted to build this heat exchanger to reclaim some of the heat that is lost up the chimney of my wood stove. I use the wood stove to heat my workshop during the winter months . I have seen heat exchanger units available in stores for around $160. Since I'm cheap, and I hate to pay money for things that I think I can build myself,  I set out to create my own heat  exchanger. 
 
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Step 1: Materials and Tools Used

Materials
  1. 2- 12" x 12" pieces of 19 gauge sheet metal
  2. 8- 1-1/4" diameter thin wall steel pipe pieces 11-1/4" long  ( I used Galvanized top rail from chain link fence)
  3. 1- 2-1/2" diameter thin wall steel pipe 11-1/4" long          ( I used Galvanized fence post)
  4. 1- 5 gallon steel bucket , the type that Tar, Asphalt roof coating or Driveway Coating come in.
  5. 2- 6" diameter black steel stove pipe unions
  6. 1 -Can of High Temp Stove Paint
  7. 1-Tube of High-Temp Fireplace Cement
Tools I used
  1. MIG Welder
  2. Bandsaw
  3. Chopsaw
  4. Bench Grinder
  5. Angle Grinder
  6. Rotary Tool
  7. Tin Snips 
  8. Various Drill bits
  9. 1-3/8 " diameter Knockout Punch

Step 2: Preparing the Steel Pipes

Picture of Preparing the Steel Pipes
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      I used left over pieces of galvanized fence posts and top rail for the steel exchanger pipes. I cut 8 pieces of 1-1/4"  pipe to 11-1/4" in length. One piece of 2-1/2" pipe was also cut to 11-1/4" in length. After the pieces were cut , I removed any remaining burrs from the inside of the pipes. Burrs left behind will impede the air flowing through the unit. 
     The fence pipes that I used were Galvanized.  The Zinc coating on the pipes needs to be removed before the pieces can be welded safely. Breathing the fumes from burning Zinc can cause illness. Usually I would use a grinder to remove the Zinc only in the weld area. Since this thing is going to be pumping air into my work space, I wanted to be sure and remove all the Zinc to be on the safe side. The easiest way I could come up with was to use Muriatic Acid. I put all the pipe pieces in a bucket with enough water to cover them all, about 2 gallons. Then I poured in about 2 cups of Muriatic Acid. I left the pipes to soak outdoors. After about 2 hours all of the Zinc coating had lifted off the steel and was floating around the top of the bucket. I rinsed the pipes thoroughly with water and dried them off.  I neutralized the remaining acid solution with a box of Baking Soda before discarding it.


 *Note about Muriatic Acid*

     Use extreme caution when handling Muriatic Acid.  Acid can burn the skin and severly damage the eyes. Wear rubber gloves and eye protection at all times when handling acids.

      Muriatic Acid is a powerful acid used by cement workers to clean concrete from tools and such, it is also added, in diluted solutions, to swimming pools to adjust the P.H. levels. You can purchase Muriatic Acid at most home centers and Hardware stores for about $8 per gallon.


Step 3: Preparing the End Caps

    I started by laying out the pipe locations on the 12' x 12" pieces of sheet metal. I first located the center of the piece. Then laid out 8  center points for the pipes equidistant around a 3-3/4" diameter circle. The holes for the pipes needs to be 1-3/8" diameter. On the prototype version I drilled the holes with a step drill, then ground them to their final size with a Rotary tool with a carbide cutter bit installed. This took a long time and was not much fun at all. This time I used an electricians Knock Out  punch. I was able to borrow one from a friend that  was exactly the size I needed. The K.O. punch requires a 3/4" hole in the metal to be able to be inserted. I first drilled a small pilot hole in each location using a center drill for accuracy. Next I drilled the holes out to 1/2" diameter. Finally, I used a 3/4" drill bit to achieve the final size.
    To use the K.O. punch, the circle cutting die is un-threaded off of the shaft. The shaft is then inserted through the 3/4" hole previously drilled in the work piece. The bolt is then tightened, pulling the cutting die through the sheet metal , creating a perfect hole. I used a pneumatic impact gun to tighten the K.O punch and speed things up.
    Next, I cut the outside shape of the end caps. To do this, I needed to determine the diameter of the bucket that I was using for the housing of the heat exchanger. My bucket was tapered , so one end of the the unit has a 11-1/4" diameter and the other end is 10-1/2" diameter. To cut the end cap in a nearly perfect circle , I used a vertical band saw. I drilled a 1/8" diameter hole in the band saw table the distance away from the blade equal to the radius of the circle desired. I also drilled a 1/8" hole in the center point of the end caps. I then inserted a 1/8" steel pin through the hole in the sheet metal, into the table of the band saw.  Before I started cutting the circle, I had to trim the sheet metal in one spot to allow a location for the band saw blade to begin cutting. Now insert the pin through both holes, turn on the saw and rotate the sheet metal around the center pin to cut a circle.
    Finally , I cut the 2-3/8" center hole. To do this, I drilled a series of 5/16" diameter holes around the circumference of the circle.  Then I used a Rotary tool and carbide cutter to achieve the final shape .

Step 4: Assembling Heat Exchanger Core

    Now it is time to assemble the heat exchanger core. I made a Jig to aid in holding the pipes in place while I'm welding them.To make the Jig, I laid out the same hole pattern as the end caps on a piece of 3/4" plywood. I used a 1-3/8" diameter Forestner bit, in a drill press, to drill a 1/4" deep hole at each location. I set the depth stop on the drill press to assure that all of the holes are the same depth. The Forestner bit bores a flat bottomed hole allowing the pipes to stand straight up.
     I started assembly by aligning an end cap over the wooden assembly jig. Then I inserted the first pipe section, held it in place with a magnetic welding clamp and welded a series of tacks to secure it in place. I made sure to check the squareness of the pipe several times while tack welding it in place. These tack welds will be on the inside of the heat exchanger when completed. I continued welding the other 7 pipes into position in the same manner. Once all 8 1-3/8" pipes are in place, the assembly was removed from the wooden jig. Next I aligned the opposite end cap on the wooden jig, then carefully inserted the opposite ends of the asssembly into the jig. Again I made sure the pipes were perpendicular to the end caps and tack welded them in place. I then removed the assembly from the jig and welded a bead around the entire circumference of each pipe on the outside surface of the end caps. The final step was installing the center, 2-1/2" diameter, pipe. I did not use the jig for this step, instead I held it in place while I tacked it in.

Step 5: Preparing the Housing (Bucket)

Picture of Preparing the Housing (Bucket)
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     When I originally began to build the first prototype, I arranged the exchanger pipes in a rectangular pattern. I was planning on building the outer housing out of sheet metal, in a box shape. Then I had the idea to use a metal bucket. Perfect, it comes pre-made, and the round shape will help with the flow of the chimney. Now to find a bucket. I used an Asphalt Roofing Cement bucket. First I had to clean all of the cement out. To do this I first sloshed some mineral spirits around the inside of the bucket. This removed most of the roofing cement that was still wet. To remove the dried cement I decided the easiest way would be to burn it out. I started a fire in my outdoor fire pit, poked some holes in the bottom of the bucket, and placed the bucket upside down on the fire. I let the bucket burn for about 20 minutes. The previously hardened roofing cement was reduced to ash and could be removed with a wire brush. Once the bucket was cleaned up, I used an Angle grinder with a fiber cut-off wheel installed to cut the bottom of the bucket off.

Step 6: Installing Chimney Inlet and Outlets

     The chimney inlet and outlet are fabricated out of  6" stove pipe unions. I purchased them for $7 each. I inserted the heat exchanger into the bucket while aligning and laying out inlet/outlet locations. Without the exchanger inserted, the bucket becomes oval in shape. The first thing I did is get the bucket propped up level. The bucket I used was tapered at the bottom , so I had to set it up on some shims. I also used the brackets that held the buckets handle in place to aid in alignment.  I was able to measure up from the table to the brackets to verify that both sides were equal distance. This is important when you prepare to locate the outlet on the EXACT opposite side of the bucket, so that the unit will be properly aligned when installed in the chimney pipe..
      Once the bucket was all set up good, I was able to continue laying out the inlet/outlet hole locations. This was an eyeball procedure for me. I set the union on the bucket and centered  it by eye. Both the union and the bucket have a bead/rib rolled around them for added rigidity. I located the union so that its bead would contact the bead on the bucket. This area is more rigid than the rest of the bucket making it a good location for welding. the stove pipe unions are not exactly round. They have a flat side where the seam is. I was sure to keep the seam in the same position while fitting the unions. When I was satisfied with the location of the union, I used a paint marker held tightly to the union to mark the location. I used tin snips to cut out the opening, trimming carefully to try and make to hole just large enough to allow the union to fit as tight as possible. Once I got a good fit, I slid the union into the bucket, then used a paint market to draw a line around the perimeter of the union.
   Next I removed the pipe union from the bucket and offset the line I just transferred by about an inch. I then used tin snips to cut the union to length, cutting on the second offset line. After the union has been cut to length, I made a series of cuts perpendicular to the remaining marker line, spaced about 3/4" apart, around the entire perimeter of the union. Then I re-inserted the union into the bucket, with the exchanger core removed, and folded all of the tabs over to hold the union in place. I also used a hammer to aid in bending the tabs. 
    The final step is to carefully weld the union to the bucket. This was tricky for me because the walls of the metal bucket are only .015 of an inch thick, making it very easy to burn through while welding. Before welding, I used a wire wheel mounted in a angle grinder to remove the paint from both surfaces to be welded. I made a series of "tack welds" to secure the union in place. I'm sure it is not impossible to weld a continuous bead around the seam, but my welding skills are limited. All of the gaps that are left between my weld tacks will be taken care of later in the instructable.
      Now it is time to repeat this procedure on the opposite side of the bucket. Take care to align the chimney inlet with the chimney outlet, to assure that the unit will fit properly in place.
    
    

Step 7: Installing Heat Exchanger Core

    This step is pretty straight forward. After installing both the chimney inlet and outlet, I inserted the heat exchanger core into the bucket. Again I fastened the core into place with a series of tack welds, trying my best not to burn through the thin metal on the bucket. Once the core is secured in place, I applied a bead high temperature fireplace mortar to all of the welded seams. The mortar comes in a caulk tube which makes application fairly simply. I followed the directions on the mortar tube and moistened all of the seams with water before applying. I caulked the circumference of the exchanger core at both ends, and also the chimney inlet and outlets. The caulk covered all of my ugly weld tacks as well as sealing all of the gaps between the welds. After the mortar dries for at least 24 hours, it must be "fired" to cure it. Before firing the mortar, I painted the entire unit with high temperature wood stove paint . After 1 hour of drying, the paint too must be "fired" to cure it as well.


   * A note about sealing the gaps*

     Dont worry if some small gaps remain in some of the seams, most likely they will not leak any smoke into your living space. Once a draft is established in the chimney, the smoke just flows on past the gaps. You can see actual holes in my chimney pipe in some of the photos, below the heat exchanger unit,  from previous experiments.  I could have repaired the holes, but I like them there. They give me a way to monitor the intensity of the fire in the stove, as I can see fire shooting up the stove pipe and into the heat exchanger.  It is possible to get some smoke leakage into the room. This happens when I open the stove door while I have the chimney flue damper partially closed off. I will get a few small puffs of smoke out of the holes in the stove pipe, as well as the seams in the top of my stove where the removable lid is located. No big deal. I gives my shop the nice aroma of burning wood. Sometimes I cause this to happen on purpose, just for the smell.

Step 8: Installing the Heat Exchanger

Picture of Installing the Heat Exchanger
    Installing the heat exchanger in my wood stoves chimney pipe was pretty straight forward. I measured and removed a section on stove pipe to accomodate the unit and slid it in place. The next thing I did was to get the fire started in the stove. I got a pretty good sized fire going, nice and hot, to "cure" all of the fireplace mortar and stove paint. This part was quite smelly. The paint lets off some pretty nasty fumes as it cures. I opened the door to my shop, where my stove is located, and used a fan to help circulate the smelly air out. The smell only lasted about 15 minutes. As the paint cures it turns from a glossy black to a flat black. The fireplace mortar swells up about 50% its original size as it is cured.

Step 9: Building the Circulation Fan

Picture of Building the Circulation Fan
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      I removed the motor from an old table top humidifier that my Dad gave to me. I used some metal rods and scrap pieces of flat stock to create mounting brackets for the fan. To mount the fan to the heat exchanger, I cut slits in some pieces of 1/2" square stock. I then drilled an tapped a hole in perpendicular to the slots to accept a screw that clamps the block to the thin metal housing of the heat exchanger. These "clamp blocks" were then welded to the opposite ends of the metal rods on the fan brackets. The fan blade that came on the humidifier motor had 2 problems. First, it was made of plastic. Second, it blew the wrong direction. It pulled air rather than pushed air. My Dad also had an old aluminum fan blade of the the correct diameter ( 8") laying around. This blade was also a  pitched in the wrong direction, causing it to pull air instead of push air. I looked into trying to change the rotation of the AC fan motor. I checked with a local electric motor repair shop, they said it may be possible to reverse the direction of the motor, but I would have to bring it to them and pay a minimum bench fee of $20.  I'm all about keeping my projects cheap, so instead I was able to carefully twist each blade of the fan in the opposite direction, reversing the direction of airlflow. Viola, my fan blade now pushes air through the heat exchanger , instead of pulling air through. 

Step 10: Heat Exchanger Performance

Picture of Heat Exchanger Performance
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   Well let me first say that this thing works extremely well. It really pumps out the heat. I used to use a kerosene heater to help heat my shop. With this unit I now use only the wood stove to keep my partially insulated  shop warm and toasty. I can raise the temperature from 20 degrees Fahrenheit to 70 degrees F in about 1.5 hours. Previously, using my stove alone with no exchanger, it would take closer to 3.5 hours to warm the shop up. When I really have the fire roaring in the stove , the exchanger core temperature reaches upwards of 800 degrees F. That's a lot of heat otherwise wasted going up the chimney. With a medium sized fire going in the stove, exchanger core temperature stays around 450 Degrees F.  I imagine performance could be improved by using heavier steel pipes in the exchanger core and thicker metal for the housing. Doing this would allow the unit to retain more heat and re-distribute the heat as the fire dies down, keeping  heat output more constant. Also, the large pipe in the center of the exchanger core does'nt really have much airflow through it. This is because the center of the fan blade (hub) does not produce much air flow. The center pipe could be omitted, affecting performance very little.



* A note about my work shop*

     I am using a Vogelzang boxwood stove to heat my shop. It is the smallest stove they make. My shop dimensions are 32' x 16'. It is insulated with R-13 fiberglass batt  on 3 walls and R-19 fiberglass on the ceiling. The fourth wall, which is 32' in length , is not insulated at all, due to the location of my shop. ( underneath the roll out deck of a large skateboard Half-pipe) . The stove is located in the center of the shop adjacent to the outside,insulated wall. I used concrete siding panels, mounted on stand-offs, to protect the walls from the heat of the stove. Since the shop is long and narrow, I have always used another fan ,located near the far end of the shop, to help circulate the heat evenly throughout the space. 

Step 11: Conclusion

     Well I must say that I am very pleased with the performance of this heat exchanger. I can heat my shop up rather quickly on even the coldest winter days . I no longer rely on a kerosene heater for supplemental heat. The ability to heat the shop quicker allows me to get more use out the shop in the winter months. I used to only work in there when I knew I had at least 3 hours available, due to the length of time it took to heat, and the cost of kerosene. Now I have no problem firing up the stove when the shop is 30 degrees F, returning 1/2 hour later to a shop that's at least 50 degrees F, comfortable enough to start working in. Even better I've used no kerosene, burned only wood, which comes free to me via the woods out back and pallets picked out of dumpsters. To top it all of I spent only $25 on materials to build this project. I had the sheet metal and steel fence piping left over from previous projects. I only purchased the stove pipe unions and the fireplace mortar.

     I was in a house recently that had a similar store bought unit, installed in the chimney of the boiler system, supplying heat to the surrounding area. The size and shape of of the unit could be modified to fit other applications. A smaller unit could be built with 4" inlets, and used in place on the chimney stack of a gas burning hot water heater. Alternately , a larger unit could be built with larger inlets for a 8" diameter chimney system. 
    
    Thank you for checking out my Instructable, If you are considering building a project similar to this, DO IT!!  You wont be disappointed with it's performance . I look forward to reading your comments and questions. Now get out there and build something cool and usefull yourself.......and then write an instructable and share it with the rest of us.

    
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cnel35 months ago
From a glance it looks like a steel truck wheel which could probably also be used.
goffronny 6 months ago
I use a wood stove similar to this to heat my garage that is attached to my house. I was amazed by how much the stove alone helped the entire house by heating the empty space and the attic above that is partially owner above the garage. Ian in the process of building my own exchanger for my stove. I am a welder by trade and have my own welders here in the garage but with the help of my company and some scrap, I modified just a little from this one. I rolled a piece of 18 gauge to 10". I did use my own left over fencing materials. Thanks for the muriatic acid info btw. I have in the process learned that a metal coffee can fits perfectly over the crimped end of a stovepipe and is easier to weld to the exchanger as well. Also, for those that want to try this project that may not be able to get a hole punch like the one in the instructable, I used an 1-1/4" bi-metal hole saw bit and a die-grinder to make holes the proper size. Thanks for this instructable and the incentive it gave me to use my trade and skill to make my house warmer for my family. I will add pics when my project is finally complete. Thanks again for this idea.
Bruce A.F8 months ago

The
tube blower heat exchanger will extract more heat from the smoke, but
much more heat could be gained, as much as 60%, by burning that smoke in
a secondary combustion process. The addition of a "heat drum" secondary
combustion chamber and a heated secondary air injection. This is a
crude diagram, but I have built a dozen or so by both modifying
existing stoves and by building from scratch a double barrel system
using barrels for both the primary firebox and and the secondary
combustion. Not only is greater heat produced and extracted, but opacity
of the smoke out the top of the stack cleared to near zero
particulates.

Heat drum2.png

Nice diagram man - I built an outdoor wood furnace using one of those barrel stove kits (https://diybarrelstoveoutdoorfurnace.wordpress.com... and I DEFINITELY NEED TO ADD a secondary combustion system to mine. Your diagram is really cool how it illustrates it. Another guy in one of the forums used square steel stock tubing and welded up a nice cage that has a mounting flange as well as a bunch of small drilled holes. The contraption drastically increased his heat output while also drastically reducing the amt of wood he needs to heat his home. Really awesome, thanks!

Do you have contact info ? I would like to see a finished product and get a quote on you making one and shipping.

ntense997 months ago

Hey man, this project of yours is cool - I love looking at various people's wood burning appliances! Ever think about using one of those small metal buckets that u used for your exchanger for a top-down wood feeding system? That's what I used those buckets for in my stove. I have an instructable on here under my name if you want to check it out, OR just go right to my main web site that has more detail. I build a barrel stove outdoor furnace and some of your techniques kind of reminded me of the stuff I used. Enjoy man, thanks!
https://diybarrelstoveoutdoorfurnace.wordpress.com/

SeanH18 months ago
Very nice seems like it would help a lot thanks for sharing this
Sketch112224813.jpg

Without proper cleaning, this will cause a chimney fire in short order, and in order to properly clean it one of the end plates has to be removable.

Which means it has to be gasketed on the removable end to prevent smoke and CO2 from leaking into the "people space"...and there are very few reliable high-temperature gasket materials besides Asbestos.

Nicely done! Wondering if there's any way to use a thermoelectric module to power fan(s), so that no AC needed, so it'd be totally self-generating.

Wow 1st I wan to say thank you for all the information contained in this post im in the process of creating the same thing I was looking to make something like that but did not have any direction on how to get started thanks to you now I to can make one for my wood burning stove thank you its perfect
VertDude (author)  sgonzalez221 year ago

Im glad you can use some of my ideas to create your own project. Please post a picture when you complete it..

Is that a ramp in the background or a building???
VertDude (author)  camping crazy1 year ago

Its a Vert Ramp and a building, I have storage under one side, and a 16' x 32' work shop under the other side

shannonlove2 years ago
Respectfully, I disagree about ignoring holes and tolerating loose seams. I would recommend as tight a seal as possible on a stove flue if it is used in a modern building.

I was privileged as a youth back in the 1970s to meet many older rural people who came of age before WWII and who still used the old tech. My uncle's mother, who was then in her late 80s was born in the 1890s and distrusted electric heaters. She insisted on her potbelly stove right up to the end. The upshot is that I used these old stoves a lot. 

One of the dangers of pot bellied stoves or any tech burning carbon is that if you get incomplete air flow, you get incomplete combustion which creates carbon monoxide. If you have a stove whose fuel has burnt down to coals and you get an incomplete draft and you have holes, you can leak carbon monoxide. Carbon monoxide is colorless, odor less and its effects subtle. 

Wood burnt down to coals produces no smoke and even little smell (depending on the wood). It has become charcoal at that point. With an incomplete draft, the hot air produced by the coals isn't being sucked up the flue but is just slowly drifting up it by thermal expansion alone. It won't prefer exiting the chimney over leaking out a hole. Even the slots for lifting the cooking plates become an exit point. 

In the past, this was rarely a problem because the buildings, even houses, were drafty with lots of natural air exchange. CO or other gases couldn't concentrate easily. These days houses and even work buildings are insulated to the point of being hermetically sealed. Any gasses emitted inside the structure stay there and concentrate especially overnight when no one is opening and closing doors. 

All technology evolves in an "ecosystem" of other tech. When you move it out of that ecosystem it's associated risk change. Just because a technology has been used safely for decades in one environment doesn't mean it is safe in another.

When we put a pot bellied stove in a modern insulated structure we move it out of the well ventilated environment it was designed for and put in it a closed, air recycling environment, we can make them a hazard. Extra care must be taken in their use and maintenance.




plus u 4got 1 thing that it flow down down then upwards as well. u need a small amount of air inflow in to the structure as well.

VertDude (author)  shannonlove2 years ago
Good Point and thanks for all of the information. My workshop is definately not air tight, nor is the stove, and Im not spending the night out there while the fire dies down. My risk factors are low, although I am going to take the advice of Greenman48 and install a CO meter to be on the safe side..
If your shop is naturally drafty then there really isn't any risk but carbon monoxide detectors are cheap enough that they should be standard in any environment where carbon is burned for any reason.

wat no work gloves.

ok i c now the head. ok heres a thought try filling the void with sand 4 more therm mass soaking?

u need to look at engineer775 channel an look at his water heater set up.

treed161 year ago
Cool! Great job.
SIRJAMES092 years ago
AWESOME IBLE!!
TY for sharing Sir.

I just had a brain fart. :P
is there a way to connect a 2nd fan blade to the center of the blade that is already there??
My thinking is, with the 2nd fan blade, even the center pipe in the heat will put out some heat...
or am I out in left field with this?

static2 years ago
To be stating the obvious, simply getting black pipe would eliminate the need to deal with the zinc removal. unless the galvanized was free or already on hand.
LynxSys2 years ago
That supervising head needs to get some glass between him and that arc! And really, given his lack of regard for personal protective equipment, do you really want this guy--well, head--supervising anything around your shop?

Seriously though, it's a nice and well documented project. I'd be building something similar right now if I had a metal shop of the magnitude that you do!
VertDude (author)  LynxSys2 years ago
LOL, That Head has been hanging around the shop for quite a few years now(14) . He's kind of a shop mascott, by the way, that is not my personal metal shop, just the tool room at work. Thanks for commenting..
Quester552 years ago
First, Let me suggest that the Zinc That comes off after the ACID Bath, Is Now TOXIC & Baking Soda Has NO Effect on Zinc, After it's been Chemically Altered.
Otherwise, You have a Great Project , Glad it worked out for you.
To Avoid the Zinc problem in the future, I Suggest you purchase TAIL-PIPING or Muffler Piping from a local suppler, or Get it Cheap at an auto Pick-a-Part Yard.
Here's a Trick, Find some Indian Clay in the Ground, wash 7 Filter it so you get Just the Clay & Let it build up until you can fill a 5GAL. Bucket, Keep it moist, Using Sheet Metal Flashing make 2 Round Pipes or tubes, 1' about 20" across & one about 18"
Across, Drill Holes in the Lip of the 2 pipes & use 3" Bolts, Washers & nuts, As Spacers for the 2 pipes. Once finished, you should have a pipe Within a Pipe Mold,
Now comes the fun part.
Setting the Pipe mold on the Ground, ( Note using an old Burlap Feed Sack as a Ground pad) & Fill the space with the Clay. Now Cover it up with a Breathable Screen to keep bugs out & let it dry for a few days. When the ends feel dry, Move the Mold to a Hard Dry Surface & Let it Sun dry a week longer, Then with someone to Help you, Build a Fire big enough to surround the mold( Note or Place it on a Grill & ) Bake it Keeping the fire hot for 12 hours.
If All Goes well You'll have a Poor-Mans FIRE-Brick Liner for your Hot-Water-Boiler,,
Pot Belly Stove or Backers Oven.
Just Wish I had a way of Showing you the Steps.
Good Luck.
You can weld galvanized steel safely as long as you use the correct respiratory protection, so it might not have been strictly necessary to remove the zinc (of course, there are plenty of welders who think that "proper respiratory protection" is "keepin' yer melon outta the plume!" but let's not go into that). That said, I don't think that the zinc would be affected by the consistent high temperatures of the stove pipe, but I'm not sure.
VertDude (author)  Quester552 years ago
Cool Idea....By the way, the purpose of the baking soda is to neutralize the remaining Muriatic acid...So as not to corrode plumbing pipes as it is disposed of..
confu2 years ago
Pretty nice build!

If you would have used something with a larger wall thickness as a housing, I would have recommended to weld some fins to it to increase surface.
But I think that won´t work with that bucket and its wall thickness of probably about or less than 1 mm (?!).

And in my "very own perception of fluid dynamics" (since I´m not an engineer), it would be more efficient (for the overall air flow through the pipes) to duct the fan and/or make it "pull the air through" to avoid losses due to turbulences on all those edges/protrusions.
But my GF who actually "is" a mechanical engineer specialising in thermodynamics says that turbulent flows are best for dissipating heat. Hmmm. I really don´t know.
And if you are concerned about overheating the engine of the fan if it "pulls" air, you may extend the motor shaft through the center pipe and install the fan on the other side...

An additional approach for maxing out the efficiency of your stove;
My neighbour uses an almost similar woodstove and he attached an array of steel pipes to the walls of the burning chamber to increase the surface. Seems to work pretty well (as he says).
If you like, I will ask him to take a photo of that build.
VertDude (author)  confu2 years ago
These are some good ideas, I was planning on building the original housing out of thicker steel, but then came across the bucket and it seemed to simple, so i used the bucket...a trained welder with better equipment could surely weld some fins on the bucket...I am interested in your neighbors set up, if you do get a picture..
confu VertDude2 years ago
Took a while, but here you are. He also added a "humidifier" on top now :)
IMG_1929_1.jpg
VertDude (author)  confu2 years ago
Cool.I will have to add some pipes to my stove!. Thanks for the picture.
Switching the fan to a squirrel cage type(like off of a junked van) would solve the problem of the center not getting enough air. for version 2 i would recommend to make it longer and turn it on it's side (so the hot air goes in the little tubes and you blow cold air inside the shell). this way you could make it as long as the vertical rise above the stove. and by forcing air in the top and out the bottom you start differential cooling allowing you to increase efficiency by several times. better yet it wouldn't matter what kind of fan you use as the path is no longer a straight line. so go nuts on fan size. for a better description just google vertical fire tube boiler. Great job.
VertDude (author)  absolutekold2 years ago
Thanks, I will check it out
wudwerks2 years ago
Nice work. I just bought an identical woodburner as yours, and the instructions say to keep a 36" clearance from any combustibles (including 2x4's behind wallboard). I thought about that cement board, too, but don't have much faith in it, as far as keeping the heat off my wall studs. What is your experience with this stuff, as I see your clearance is only about 12" from the walls and your workbench.
VertDude (author)  wudwerks2 years ago
Thanks wudwerks, actually my stove is about 18" in the closest spot, to the wall. the stove is sitting at about 45 degree angle to the wall. The cement board is 5/16" thick James Hardy siding, left over from my house. I used 3" long pieces of 1/2" metal tubing as stand offs,or spacers, between the cement board and the wall. I measure the temp of the board as hot as 375 degrees F , while the wall behind the board remains at 80 degrees, So I am quite confident with it, I also use a piece as an exit flange for my chimney and it remains rather cool as well. I have been using the stove in this location for 4 winters now with no problems
VertDude said: >>I also use a piece as an exit flange for my chimney and it remains rather cool as well.<<
Brilliant! I was wondering what to do about that, too! Thanks.
VertDude (author)  wudwerks2 years ago
Sorry wudwerks I had a typo in my first reply. My stove is only 8" away from the cement board in the closest spot, rear corner of stove...
zawy2 years ago
Thicker steel pipes would reduce heat exchange slightly. You want the steel to transfer the heat actually cool off as much as possible with a larger fan, not retain heat.
zawy2 years ago
The pipes need to be vertical and parallel and in front of the fan and having the hot air flow inside instead of around them, and no outside "drum". The reason is that your fan air flow rate is a lot higher (and should be) than the exhaust airflow rate, so the internal net effective duct width should be smaller. As it is, not much air as able to flow through compared to what the fan is capable of. Heat extracted will be sort of, in a wild sense, proportional to the air flow rate you can get next to the pipes. Since you're dropping the heat only about 30 F on 400 F, you're getting about 10% of what's theoretically possible. My suggested change will cause a lot more creosote and need a good bit of pipe to maintain good exhaust airflow to keep a good fire with low CO. Another option is a benjamin franklin stove (a sideways barrel on top with the inlet and outlet on opposite ends to give the exhaust air a lot more surface area than a simple pipe) . Pumping water over such systems from a larger tank (50 gallon barrel for 400 sq feet) and raised to 140F is more effective than air at extraction and releases the heat energy all night after an evening fire. Use heat capacity of air, estimate exhaust flow rate, and measure the temperature difference to calculate heat output of the exchanger. (13 watts for each liter per second exhaust flow for each 10 C drop in temperature.
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