Step 1: Materials and Tools Used
- 2- 12" x 12" pieces of 19 gauge sheet metal
- 8- 1-1/4" diameter thin wall steel pipe pieces 11-1/4" long ( I used Galvanized top rail from chain link fence)
- 1- 2-1/2" diameter thin wall steel pipe 11-1/4" long ( I used Galvanized fence post)
- 1- 5 gallon steel bucket , the type that Tar, Asphalt roof coating or Driveway Coating come in.
- 2- 6" diameter black steel stove pipe unions
- 1 -Can of High Temp Stove Paint
- 1-Tube of High-Temp Fireplace Cement
- MIG Welder
- Bench Grinder
- Angle Grinder
- Rotary Tool
- Tin Snips
- Various Drill bits
- 1-3/8 " diameter Knockout Punch
Step 2: Preparing the Steel Pipes
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
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
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)
Step 6: Installing Chimney Inlet and Outlets
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
* 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
Step 9: Building the Circulation Fan
Step 10: Heat Exchanger Performance
* 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
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.