Post by foxtatic on Nov 20, 2020 10:54:12 GMT -8
I am pleased to share my journey building "The Sherman Tank." Because builds need fun names. Watching how others have built heaters has helped me immensely, so now I'll share!
Goal- Make a powerful heater with a removable core for an poorly insulated shop. Able to be moved. Able to add mass that can be fine tuned.
Core choice- Peter Van Den Bergs DSR2 (Double Shoebox Rocket version2) Selected because the shape lends itself to my build, it's shape is such that it can be removed, it has a fun window which could become a door and oven, it's super efficient, and it can be ran as a simple open system (no door or secondary air tube, BUT those can be added later in this design.)
Material choice- Ceramic Fiber Board for the core because it is light weight, lending itself to removal. And because it's easier to work with than castables or firebrick. A 300 gallon steel tank for the housing/bell because I had the big ugly thing in my yard already and it fits the bill of an inclusive shell that can be moved, rather than built in place from things like brick and/or cob.
Sizing- I chose a 7 inch system to use with 8 inch flue pipe for better guarantee on proper draw. Also liked 7 inch because it fit my firewood and my tank. The one measurement you can adjust in a core is the firebox length, which I took from 20 inches to 24 inches. This also matched the longest edge of the CFB sheets. Someday I will move a system into my home which has an existing chimney with 8 inch flue.
Problems- Despite the best advise not to, I ordered CFB online, shipped to me. It was damaged. I was able to get a partial refund, but freight or in-person buying is the correct way to go.
There is bad CFB out there, and that's what I got from Phoenix Supply. It did not take the flame well. Spraying the pieces with sodium silicate saved the day. Now instead of fraying, the CFB just gets harder. I did have to water down the thick 40% sodium silicate solution by a third to be able to spray it. A little blue dye helps you see where you've covered.
I'll tell the build story mostly in pictures, but here are a few videos also:
-The initial CFB material test results. This was rather disheartening youtu.be/lwmUGAVHQtk
-The smokeback at the beginning of the burn, likely caused by me still figuring out how to properly light the thing! I was able to fan it back to start the proper burn path youtu.be/JXbv9jMCT7k
-The roaring takeoff of secondary combustion. A great pleasure to behold in real life youtu.be/DS-EtrIa7iA
-Even smokeless burning at about the 20 minute mark. I bet it would have been sooner if I had lit properly (plus the tank residue) youtu.be/hI91G6SjNl8
Using an infrared temp gun, I got the following readings:
500 to 550 degree F Max top temp right above the exit port of the core. Otherwise tank top was 400 to 500.
200 degrees at flue base (where it meets the tank top) but 180 above that.
Towards the end of the burn the whole tank read more evenly around 300 degrees.
Conclusion- Well over a year ago, I started studying rocket mass heaters. And to build one, it takes lots of studying! You have to determine your goals, your style, your materials, then run into obstacles until you hammer out something that will then need a bunch more refinements. Special thanks to Peter Van Den Berg, Matt Walker, Thomas Rubio, Gerry Parent, and all the folks on Donkey's board. Most of this core came from studying the 31 pages of Peters DSR2 build here: donkey32.proboards.com/thread/3503/double-shoebox-rocket-mark-ii
Next up- I'll do an update post when I move it into the shop. This will include how I'll add thermal mass, and how the chimney will interface.
Any comments, criticisms, and questions are welcome!
CFB damaged from shipping.
My cheap CFB could not stand the heat.
Treating with sodium silicate made cheap CFB "Super CFB." No more fraying.
Tested all measurements and sizing with foam before cutting CFB. Excessive maybe, but I discovered a few design mistakes.
All parts ready for sodium silicate treatment.
Stainless screws used in high heat exposed areas.
Three inches may seem excessive for the stub, but per design notes the riser stub must be "less wide" than the fire box and top box.
Nubs from shipping damage trimmed and re-treated. Gaps stuffed with super wool.
The ugly tank in my back yard will get an upcycled new life. It's best to just do these things without telling your wife your intentions.
Angle grinder and reciprocating saw did the job.
Drained 2 gallons of fuel, scraped the sides, and pushed sludge the sludge out.
Bath by fire to clean the residue out. Torch kept going out in the tank because DUH, it was eating all the oxygen.
1/2 inch holes and a few jig saw blades. Torching the inside got a lot easier after this additional hole.
Paint removed with scraper and flap disc on the angle grinder.
Flue suspended 8 inches from floor, spaced one inch off back wall with extra nuts.
Didn't quite fit, needed a little more grinding.
The Sherman Tank! Stainless eye bolt that acts as the bypass handle is visible up top.
Wood and sticks likely too damp to be good fuel, but burned fine.
Soot and condensation quickly burned off.
Discolored firebox but CFB in good shape.
Goal- Make a powerful heater with a removable core for an poorly insulated shop. Able to be moved. Able to add mass that can be fine tuned.
Core choice- Peter Van Den Bergs DSR2 (Double Shoebox Rocket version2) Selected because the shape lends itself to my build, it's shape is such that it can be removed, it has a fun window which could become a door and oven, it's super efficient, and it can be ran as a simple open system (no door or secondary air tube, BUT those can be added later in this design.)
Material choice- Ceramic Fiber Board for the core because it is light weight, lending itself to removal. And because it's easier to work with than castables or firebrick. A 300 gallon steel tank for the housing/bell because I had the big ugly thing in my yard already and it fits the bill of an inclusive shell that can be moved, rather than built in place from things like brick and/or cob.
Sizing- I chose a 7 inch system to use with 8 inch flue pipe for better guarantee on proper draw. Also liked 7 inch because it fit my firewood and my tank. The one measurement you can adjust in a core is the firebox length, which I took from 20 inches to 24 inches. This also matched the longest edge of the CFB sheets. Someday I will move a system into my home which has an existing chimney with 8 inch flue.
Problems- Despite the best advise not to, I ordered CFB online, shipped to me. It was damaged. I was able to get a partial refund, but freight or in-person buying is the correct way to go.
There is bad CFB out there, and that's what I got from Phoenix Supply. It did not take the flame well. Spraying the pieces with sodium silicate saved the day. Now instead of fraying, the CFB just gets harder. I did have to water down the thick 40% sodium silicate solution by a third to be able to spray it. A little blue dye helps you see where you've covered.
I'll tell the build story mostly in pictures, but here are a few videos also:
-The initial CFB material test results. This was rather disheartening youtu.be/lwmUGAVHQtk
-The smokeback at the beginning of the burn, likely caused by me still figuring out how to properly light the thing! I was able to fan it back to start the proper burn path youtu.be/JXbv9jMCT7k
-The roaring takeoff of secondary combustion. A great pleasure to behold in real life youtu.be/DS-EtrIa7iA
-Even smokeless burning at about the 20 minute mark. I bet it would have been sooner if I had lit properly (plus the tank residue) youtu.be/hI91G6SjNl8
Using an infrared temp gun, I got the following readings:
500 to 550 degree F Max top temp right above the exit port of the core. Otherwise tank top was 400 to 500.
200 degrees at flue base (where it meets the tank top) but 180 above that.
Towards the end of the burn the whole tank read more evenly around 300 degrees.
Conclusion- Well over a year ago, I started studying rocket mass heaters. And to build one, it takes lots of studying! You have to determine your goals, your style, your materials, then run into obstacles until you hammer out something that will then need a bunch more refinements. Special thanks to Peter Van Den Berg, Matt Walker, Thomas Rubio, Gerry Parent, and all the folks on Donkey's board. Most of this core came from studying the 31 pages of Peters DSR2 build here: donkey32.proboards.com/thread/3503/double-shoebox-rocket-mark-ii
Next up- I'll do an update post when I move it into the shop. This will include how I'll add thermal mass, and how the chimney will interface.
Any comments, criticisms, and questions are welcome!
CFB damaged from shipping.
My cheap CFB could not stand the heat.
Treating with sodium silicate made cheap CFB "Super CFB." No more fraying.
Tested all measurements and sizing with foam before cutting CFB. Excessive maybe, but I discovered a few design mistakes.
All parts ready for sodium silicate treatment.
Stainless screws used in high heat exposed areas.
Three inches may seem excessive for the stub, but per design notes the riser stub must be "less wide" than the fire box and top box.
Nubs from shipping damage trimmed and re-treated. Gaps stuffed with super wool.
The ugly tank in my back yard will get an upcycled new life. It's best to just do these things without telling your wife your intentions.
Angle grinder and reciprocating saw did the job.
Drained 2 gallons of fuel, scraped the sides, and pushed sludge the sludge out.
Bath by fire to clean the residue out. Torch kept going out in the tank because DUH, it was eating all the oxygen.
1/2 inch holes and a few jig saw blades. Torching the inside got a lot easier after this additional hole.
Paint removed with scraper and flap disc on the angle grinder.
Flue suspended 8 inches from floor, spaced one inch off back wall with extra nuts.
Didn't quite fit, needed a little more grinding.
The Sherman Tank! Stainless eye bolt that acts as the bypass handle is visible up top.
Wood and sticks likely too damp to be good fuel, but burned fine.
Soot and condensation quickly burned off.
Discolored firebox but CFB in good shape.