Howard Hoffman

Hello Scott- I looked through all the Uncle Mudd videos I could find. I have for years seen the cobb benches for mass heaters and also for the Liberator  which I have something like. I didn't really see any videos doing something like I want to do which is without a bench or wall somehow get more heat retention from my heater. At present as long as you are burning it you have heat but when fire goes out or down the cool down in house is almost instant, at least very quickly. In looking at my situation I can put something on the round top of the stove. I was thinking maybe a stack of regular old bricks. I am not a scientist but remembered years ago people would put warmed up bricks at the foot of their bed so maybe this would hold the heat or maybe I should try to build a cobb barrel on top of the heater. I have a good 4 feet below ceiling to catch or retain the heat. If you see a particular video I have missed with something directly on top of the stove if could could maybe post a link as I have never seen anyone do what I am asking about.

I have a stove I built very similar to the Liberator Rocket Stove. I don't have room to put in a large mass bench like many off gridders are doing. I do have room on top of the stove. The question is what would be best to store the heat? I could use bricks or a metal bucket with sand. What would be the best thing I could use on top of the stove to continue to radiate heat Thank you

I have a question about this type of stove I have built one like it and don't have room for a mass- with this exception- on top. So what can I or what should I use to capture heat. I could put a lot of brick up there- that would seem like it could hold heat or could I put a metal bucket of sand up there to continue to radiate heat when fire dies down???

Hello - I am getting ready to build another rocket stove. My design is something similar to what the company with a brand name called " Liberator " is.
I have made one before and am going to build another hopefully with some improvements. The " Liberator"  company seemed to use 5" square stock for the feed tube, burner and rise and I did as well as this was a material fairly easy for me to get. I am certainly a novice at the whole thing having only built 1 stove. I have seen several reviews of their stove and it seems as though they are lining the inside of the riser with a fire brick bolted or screwed to the side of the 5" tube- here is the link in which I saw this---- https://www.youtube.com/watch?v=hG5iRgeK13g----- you can see what I speak of at 15:45 in on video. Several questions- the fire brick seems rather long ( looks like it goes all the way down) is this really firebrick ? can you drill firebrick?  how do you drill through it? and where do you get such a long product?(most I see are 9" long-these seem maybe 30" long)

I've got a question about insulating a burn tube riser. I use 5" square stock tube for burn chamber and riser. How would it work out or has anyone used a 8" stainless triple wall pipe to insulate the burn tubing and then fill in empty space between square tube and burn riser with vermiculite. There is already insulation in a double wall pipe -it would seem this may do a good job. has anyone had any kind of experience with doing something like this? Thank you for your input

Thanks to all who have answered my questions in response to my video. I have watched so many videos of these stoves which have been so amazing. I made another question post which I don't believe anyone saw so I am putting it here as so many seem to answer. I am getting ready to build another heater. I have some 5" square tube lying around so this again will make my J Tube- might as well use up stuff I kind of have. I am going to use the perlite as suggested rather than sand as insulator. I try to remember all I have watched and seen however in my curiosity I get some of it jumbled up. In my original build I did make the heater in many ways similar to the Liberator stove. The height of this is close to the video Paul Wheaton has using a 55 gallon drum as outside of the whole chamber. I believe some have said in videos maybe even Paul that the stoves don't have to be that tall. Question 1) Is there an optimum height of overall stove. Question 2) A previous reply said I need 3" clearance instead of 2" at top of J Tube- is 3" the optimum clearance for this Question #3 what is optimum clearance/space between  J-tube and insulation chamber and also the optimum clearance between insulation chamber and outer barrel. I have a bunch of junk laying around to use however if the chamber pieces I have are not a good diameter I can look around for some other things to use. Of course on the height/ clearance at top of J tube this is just a matter of cutting to size. I know the biggest difference or improvement will be the perlite compared to sand to which I thank all for pointing out. I would like to use the best height and clearance ratios to make the new stove a bit better. Thanks once again for your replies. I may not have this stuff perfect but I have been able to cut my dependance of fuel oil down using the stove I already built. As a bit of help or suggestion I get some woods chips for free delivered by tree cutting companies which I use for some mulch and if I have some of the chips dried out I drop them down the J tube along the burning process which is kind of cool as I don't have to split those up.

Hello one and all. I know there are some very good designers out there and so i have already had some information given to me about a new build to extract more heat. In the asking and sharing of information a couple things were shared and this also brought other questions about optimum size/ height/ clearance. I will include a basic drawing I made which is a fairly typical build design if you are using metal. We have a 5" J-burn tube surrounded by two metal barrels, the first or closet one to j burn chamber insulated. Now the questions. In inches what should be the best clearance between J burn and first barrel and then best clearance in inches in between inner and outer barrel. Please excuse my spelling it is terrible. Also I had saw a video which Paul Wheaton I believe said the outer casing barrel could be shorter which of course means the burn chamber is shorter. Is there an optimum height for this and what would be from your research the optimum height clearance between the j bun chamber and the top of outer barrel.

Thank you Glenn- this seems as a good resource. I will continue to try to learn and am doing more research like this to improve for the future. I am understanding this a bit better now. My idea of insulating the J tube burn area was maybe ok (although wrong insulator) -the real flaw I see now is that even if that mass of sand heated up which I am sure it does, it is setting inside of the outer barrel and not much heat is actually going to transfer into house. Cobb on the outside of the barrel would give some mass to continue with heating room. I will see about the book. I do have a thought since you mentioned  the cobb. Let me know if I am even close to being right. Trying to get the right diameter barrels or tubes took me a while. in the changing world here you can't poke or look around in scrap yards- my outer barrel was a hot water heater and none of the scrap yards would sell me one even though you could clearly see them in piles. Enough of that story I do have a resource to buy flat steel for not to terribly high a price. How about if I took the J burn tube -built a  square box around it -filled that box with perlite or vermiculite, then build  another square box on the outside of that to contain the smoke to send out and up house chimney and then made a third box on the outside which could be filled with cobb. The idea being the cobb couldn't fall off as the walls of the outer box would hold them to the smoke box. Does this sound more reasonable then what I have done previously? Thank you.

Thank you Gerry- I am slowly but surely getting this wrapped around my head better. A few years back ran across a video of a rocket mass heater and it was super cool. I knew I didn't have the capacity in home to build the Cobb style. I also saw a commercial model called a Liberator which I think I loosely pattern my build after. Has the idea changed about the height/ clearance of my J channel burn tube. When I was watching other video's of builds I do remember numerous people saying to make sure that tube came kind of close 1.5 to 2 in to top of your outer barrel. I don't have to use the fan all of the time but instead of running a preheat propane torch in the throat of the burn chamber to force the warm air I use the duct booster fan to get the air flow rally shooting up the chimney so I don't have a backdraft (which I have had) starting. I have experimented with running the fan when the stove gets going good to see if I could really get it a whole lot hotter- it does burn hotter but not crazy hotter. I may be expecting too much from my stove. There is no cobb or mass other than my inner barrel with sand surrounding my J-tube burn pipe. WE actually get fairly good heat from the stove and burning scraps has saved us money from our regular heat bill- the issue is you have to feed and fool with it all the time because when the fire goes out the place does not have that mass and so it gets cool kind of quickly. I thank you for your response.

When the stove gets burning it does have some smoke but not anywhere near as much as in times past when I had a conventional wood stove. I may be getting some of the effect but not full as I have the good rocket sound but not have the afterburn?-maybe if that would be correct. Because I had wooded floors and not a ton of space extra in the house my thought was that the sand barrel around the riser would kind of be like an inside mass so that although I didn't have a cobb bench I may get benefit from the barrel inside filled with sand. I am not sure that idea produced that much lingering heat. I have been impressed by the people who have the long cobb benches and fire their stove up for a couple hours and then don't light it or burn it anymore until the next day. I can't quite do the same and no being an engineer or maybe scientist I simply said hey I've got some sand- the sand should hold some heat after it heats up and continue radiating like the cobb bench. It is possible it does yet the inside barrel is a good 1 1/2 inch away from the outside barrel so how much heat will actually go from that inner barrel?? no so much as we get good heat with the heater as I said around 600 degrees which is much lower than others but you do feel the heat in the house and you do have the rocket sound- the problem or issue kind of is you must feed it all day long with these very small pieces of wood or if it goes out the temperature drops rather quickly in house.