New build heater smokes terrible

I have a question for all the experts here. I will describe my situation. I have just built a rocket heater after watching I think a hundred others doing the same. I don't have measurements exactly but let me describe and maybe you guys who really know these things can advise.  I may even use the wrong terms-please forgive me. The burning and wood feed area are made of 1/4 inch thick 5" square tubing. As others did I made this like a big L- the top of the L comes to about 1 3/4 inches from the top of the outter barrel. I used an old hot water heater shell for the outter chamber. I do not have the same mass type as others have because I did not think my house could support the weight of all the cob. I have regular 6" exhaust stovepipe from the hardware store. The outlet from the stove is at the bottom of the outter burn (hotwater heater) shell. The heater is about 36" high. The short end of the L (5" tubing) has a door with a handle and also gasket material just as any other wood stove. The portion that the wood feeds down from is cut and welded in at a 22 degree angle as many ither do. The otter chamber is 16" I do have a small amount of mass. I took some sheet metal and made a smaller open barrel I guess you could say to surround the square tubing. It comes up about 26 inches and is filled with sand. I did this to create at least a little bit of mass to radiate some heat after fire goes out even if I could not build a sofa out of cob. I just hooked it up yesterday. It had been outside and of course the whole thing was cold and when I went to start it smoke smoke smoke - I mean we had to open every window and door. I thought ok this is because stove is cold very cold from being outside. Well today it is inside and I have other heat so home is warm. My stove is to kind of be a suplimental sourse, anyway I think it will start good today, no such luck. When I started it it was worse I think that yesterday. This stove goes into a regular masonary chimney which has a clay liner. The house is a cape cod. When the stove gets going it seems ok. I mean the chimney outside smokes which as I see others videos seems bad because other people have heaters that produce no smoke. I do get a rcket sound but I don't think my stove burns quite as hot or effecient as others but thats ok i guess but I can't use this thing if every time IO go to start it I have to open every door and window. Does anyone have an idea of what I am doing wrong? I put some small sticks in the down feed and in the bottom I open the hinged from door and have some paper in there which I light. If I leave this door open it smokes terrribly terribly out the top . I close the trap door and used my wife's hair dryer to force air down the throat of the wood down feed area. It was still smoking but if you pulled the hair dryer away immediately the smoke cut into your eyes so bad I almost fall down. I don't quite understand this because if when it gets going it burns reasonably welll what is the start up problem. Can someone please advise? Try to use very kindergarden words I don't understand the technical jargon. I simply tried to do as close to what others did other than the cob sofa as I could but yet there is certainly a problem. Please Help

If I understand your description, you've made what is commonly seen on Youtube, a rocket stove made from square steel and then have a metal barrel sitting over the top of the L, and the tall riser part of the L has sand packed around it? If all of that is correct, I think that build is going to have serious draft issues based on the design.

Unlike a lot of Youtube videos, I don't think you'll find many here that would recommend using metal in the burn tunnel or riser, because a properly functioning rocket heater will destroy that metal very quickly. To get it to perform better, I would replace the sand with perlite or an insulating material like Superwool. That insulation should surround the burn chamber and the heat riser, some will use insulated firebricks as well. A popular riser setup is known as the "5 minute riser", which is a piece of 8" duct with 1" refractory blanket like Superwool inside to make a 6" riser, or 10" pipe to make a 8" riser.

That insulation keeps the riser hotter than the surrounding insides of the barrel, which helps draft. The other insulation helps keep the heat in the combustion area, to provide the maximum heat for the best combustion. Other than the chance a piece of paper or other material is blocking your airflow somewhere in the barrel, I expect it's the metal+no insulation causing draft issues. I would really recommend removing it from the house for further testing, to avoid any CO in your indoor air, or get a CO detector sitting nearby at a minimum.

Thank you for your information. I did build the heater with all metal parts as I have seen these in videos on youtube. I have seen the other types you spoke of and am at least visually familar. I did this kind of design because I thought it may be somewhat lighter although it still weighs a couple hundred pounds and it may just be a crazy thought that the other build would be heavier. I do not have a slab foundation or used in a garage and so I seeing others thought my version would be good enough to burn up the scrap and limbs around here and cut down a bit on the heat bill while giving me a bit of exercise busting it down cutting up and such. I am not an engineer just a guy who see some other people do things and says hey I think I could do that and so this is what I did. I did run into a somewhat similar problem a few years back with a conventional wood stove. I was living in a salt box style house with a basement. I built this house and I am fairly good at cutting and nailing but masonary- not so ,much and so the house did not have a chimney. I decided to burn some wood in a regular cast iron wood stove - I vented the stove with regular 6" stovepipe although I did use stainless so it would not rust. I made a couple brackets to hold the chimney upright. That 6" chimney was about 22' tall. When I tried to start stove same problem happpened. I did not have internet in those days but put my thinking cap on and thought hey maybe the metal pipe is cold and won't let the chimney pull air up while it is cold. I used a fan to blow air into the stove and eventually got a fan to go into the stovepipe blowing smoke up chimney until pipe was hot- once pipe was hot no problem. I did not think this would be a problem here because the stove vents into a masonary chimney with plenty of draw and the stove although metal is sitting in a heated room actually in general vacinity of other space heater.  I don't quite understand about the metal causing the draw problem if the stove is not real cold. I mean the room temperature is 72-75 so that seems kind of warm enough but again I am not a scientist or engineer. If I made a different chamber as you suggest with a blanket or other insulation then my draw is going to improve or my start up will not smoke?? This I wish to make sure of. Is there a video you could recomend with a kind of free standing stove- this is what I would need to build or retrofit mine to? Thanks

Hi Howard, to put it in basic terms ...there are certain areas and components where metal is not a suitable material to use, as  a properly operating, rocket stove is constructed and designed to operate at temperatures beyond the ability for steel to have any longevity and it will quickly degrade.

The heat riser is particularly important and needs to be efficiently insulated if you want a clean burn.

In recent years Ceramic fibre products have proven to be extremely effective in the rocket stoves construction and are easy to use.

There are many threads on this forum that show how a basic J tube can be constructed, if you just want an instant space heater with no heat holding mass, then they are quite easy to build and very basic in design but you need to use proper refractory materials and insulation in the correct areas.

Ceramic fibre is available in several forms, namely ... flexible matting and ridged board, with these products it is possible to construct a long lasting and highly efficient rocket stove.
There are other materials that can be used like refractory cement or clay, insulation materials like perlite, vermiculite that can be mixed in with the clay but they will be far more time consuming to work with .
A basic 6” J tube built with ceramic fibre products and a steel barrel radiator will produce huge amount of radiant heat with no visible smoke exiting the chimney.

Howard Hoffman wrote: the top of the L comes to about 1 3/4 inches from the top of the outter barrel.

Well, first, this is no good! 2 3/4 if you want, not an inch shorter!

Due to turbulences of changing direction, gases don't flow smoothly there and need more space.  http://donkey32.proboards.com/thread/1406/calculating-ring-circumference-projection-gap

You will have to familiarize yourself with terms like CSA or cross sectional area.

One question, do you ever see those mad welders of youtube, do follow ups often?  One year, or two years, of functioning?

Most are "bodgers" as the brits say.  They bodge things up, and don't give a damn shit about it's quality!

And anyway, metal is doomed!   https://permies.com/t/52544/metal-burn-tunnel-heat-riser


A  very nice example of a detailed build, which works straight out of the box.  


https://permies.com/t/122458/Advice-RMH-build-Hokkaido-Japan  

My build, i'm on the fourth heating season.

https://permies.com/t/44806/Cobbling-workshop-heater-cooktop-oven

With detailed construction, and follow ups.

There is several others, but you will have to dig.

Hello all- I thank several of you for your very quick responses. I will have to do some more building probably in the spring of different design however I have discovered something just this morning about smoking or not smoking on lighting. In years past I used to do some chimney cleaning as a side business. One of the simple things I would do if someone said chimney was stopped up was to take a match or twisted up piece of paper and move in front of flue opening. If chimney was clear the flame would bend or suck right toward the chimey flue bending more as you got the flame closer. This morning I took a small piece of paper lit it and put it to top  the feed tube- the flame bent down. Now my ash door was closed. As I have described before I watched others build and use stoves- it seems as though they lit their heater through the ash door. Well anyway as the fire was bending down into the feed tube i kept puting paper rolled up and some very small twigs. I got the stove lit up with no smoke in house. Now my stove is not real great like all the wonderful people here build for I am not having the real mass or am not using the right material so my chimney smokes at top and fire is not burning to terribly hot. I used a digital thermometer and on the burn chamber I got about 575 degrees. This is not all that effecient and I will have to design and build something else to be better but I had a couple purposes in doing this project1) suppliment heat 2) get rid of yard waste in a non wasteful manner 3) get some exercise ( get off the couch.  If my heater will burn without smoking up the house it will be ok for now. I know the burn chamber won't last but I am getting a bit of that rocket sound which is encouraging. Thank you contributors. I will continue to learn.

Well if you are content this will be a temporary design, you could just wrap the steel  with insulation, I think you would likely see a big improvement.

Hi James- thanks for the advice. I am certainly going to need to do some more investigation,On the idea of insulating the riser of the L- it is I think insulated. I put an 11" clyindrical metal tube on outside of 5" square tubing and filled this with sand. This is my portion or attempt to have some "mass" to hold some of the heat after burnout. The sand containment cylinder has about 2" of sand all the way around burn riser. I have this heater completely welded up and so until I make another it is not a simple thing to take apart. I do have a plazma cutter but it is not a bolt together thing its mig welded at every point. I am going to try to understand better what makes the rocket high heat. After getting a decent burn my highest heat reading has not been over 525 degrees and I have heard Paul speak of 2,000 3,000 degree fires- wow now thats hot and if I had that I am sure my metal even though 1/4 inch would burn up super fast. Anyway I'll learn more- this is an ongoing process. Thanks

Howard, in the heat riser of a J tube, at the bottom, it can reach 1000C° Dunno what this is in F°

A build which in interesting lately. Peter's Hokkaido J tube, reaches 371C° on top of the barrel.


My batch sustains 350C° in the oven, 370 when angry.



Your sand is a heatsink at startup, and insulation after, so yes your heat riser is insulated.

I would be really keen to see how it holds after 100 hours of burning. Or more.

One thing to be aware, if it spalls badly, you might have chunks of metal falling down the riser, and block it. Be very careful with this, as it could fill the house with CO gas.