I was living in a two story cabin with the lower level below grade on three sides. The stove was located in the stair well so that the inside rise was 16 feet using triple wall stove pipe open on the outer layers top and bottom. This scavenged a lot of heat from the flue. The door was on the end with the barrel bungs. the 2 inch bung was fitted with a pipe that ran to the back of the barrel laying horizontal with an elbow and riser to keep the opening above the ashes. With the draft entering at the back I could keep adding wood from the door pushing the fire to the back of the stove. Before I added the door I added a baffle above the height of the door from the back to one foot from the front and a pipe in the small bung running back to the chimney with holes drilled through it to supply air for secondary burn. With the tall flue and baffled air flow this heater was very efficient. To add mass to hold heat would you recommend adding it around the flue or the barrel?
Hans Quistorff : I can only talk in a general manner, and then about where you say you used to live, Insulation on the inside of the Barrel would allow for higher
controlled burn temperatures, allowing you to become smokeless sooner.
The Triple wall pipe was acting like the highly insulated Heat Riser / internal Chimney in a Rocket Mass Heater, I expect that that section of triple wall pipe was
as hot as any triple wall stove pipe ever gets ! To say it burned efficiently is also clearly a given, but I expect that a great deal of the fast flowing hot exhaust
actually got a chance to radiate much heat into the room before it was exhausted out doors ! Yes, you should be able to see some large improvements in the
Amount of heat you could store with a Thermal mass Like Cob !
In the example you gave the main heat radiator was the Barrel. Cobbing that would hold additional heat internally within the barrel and cause the Barrel to fail
sooner, and more heat would go up the insulated chimney, some additional stove pipe mounted below the barrel stove containing a fan and a simple fan limit
switch monted up stairs to turn the fan off and on would scavenge a great deal more of the heat from the exhaust flue pipe !
IF, your stove pipe was brought up to the level of the second floor and then turned at right angles (?) to run horizontally above the 2nd floor, it could then
be wrapped in cob which would hold and then slowly release the heat rather than allowing so much of it to escape up the vertical chimney.
In a Rocket mass heater, we are lining the Burn Tunnel and Heat Riser with refractory materials that resist absorbing heat beyond the immediate surface layers,
glowing orange hot and promoting a high temperature, and a very efficient burn ! In this manner there is a similarity to the way the Heat Riser and your 16 foot
long vertical chimney were working ! The similarity ends there because at the point the R.M.H.s hot exhaust gasses hit the top of the barrel and fall down the
sides of the 55 gal drum they radiate off heat, become cooler, and sink, this force and aiding force helps to then 'pump' the exhaust gases 30 or more feet thru
horizontal pipes where it gives of much of its exhaust heat, usually in the 150 degree F range ! I hope this helps, and that you will want to learn more about high
efficient wood stoves !
For the good of the craft ! Your comments/questions solicited and Welcome ! big AL
riser with Ref
Success has a Thousand Fathers , Failure is an Orphan
The big issue with metal and clean fire is that clean fire temperatures are often at the outside limits of what the metal can handle. Clean fire starts at 1200 F; iron glows red-hot starting around 900 F, and tends to permanently warp in the hottest part of the burn cycle. (If the fire burns clean from near beginning to end, there is often a higher temperature like 1800-2400 F in the middle, hottest part of the burn cycle.)
You can certainly wrap some thermal mass around a metal box stove, for better heat storage; I've seen everything from stacking rocks on top, to a brick hearth wall around it, to cobbing directly onto the stove, or the stovepipe.
but your longevity is limited by the metal, and all that masonry work may need to be removed to replace overheated metal parts.
I'd definitely back Allen's suggestion to get some masonry insulation INSIDE the firebox, for cleaner burn and longer life of your barrels. I'd also suggest looking at the masonry heater designs and rocket mass heater designs, to appreciate them on their own merits.
A Mother-Earth-News-style 'barrel stove' tends to last 3-5 years in steady use, with the barrel serving as firebox and rapidly burning out. With the rocket mass heaters' insulated masonry firebox, and the barrel serving only as a secondary radiator after the main burn is finished, we see the same barrels lasting 10-20 years and more (none wrecked yet as far as I know; the oldest one has been in use for about 25 years now).
Thank you Erica for your fallow up posts.
My wife and son both work with color charts so I am glad you cleared up the inverse nomenclature.
If I had the barrel stove to do again I would line the inside with fire brick and put the secondary burn draft under fire brick like in my current certified wood stove.
The certified stove has a layer of fire brick on top of 3 tubes that run from side to side with holes drilled through at 1/2 inch intervals drawing air from the draft chamber on the right side. The top fire bricks are 1/2 inch thick with another 1/2 inch of fiber glass insulation on top. This fibers area catches any soot or creosote falling on it and burns it off.
My future project if to build a heater for a 1920's era chicken house 100X20 feet with the south end 4 feet off the ground. I have accumulated an oil burner heat exchange unit 4X4X4 feet with top part having convoluted smoke path, and both 6 inch and 2 inch thick fire brick.
The original heater for the chicken house was a mass heater but the brick chimney was removed. It had a 16 inch cement mass from the East side to the center where the brick chimney went from floor to the ridge. I have not had time to investigate the fire box and how the flow was designed inside the mass. Will try to get that done soon.