Rocket wood stove

I am building a 8' x 20' little wooden house on wheels, you know solar powered, rain barrel water, sawdust toilet, splash shower, Wi-Fi capable and wood heat. Please see blog posting [glow=red,2,300]http://tinyhouseblog.com/stick-built/hermit-deluxe-update-2011/ [/glow] I found about rocket stoves about 5 months ago and built a rocket stove fired Barbecue, works great! Needing a low cost and a build it myself source of heat for my tiny house, I have been working out a rocket wood stove design. I have a lot of other things to do like finishing the interior of the house for now, but in a couple months I will be building the rocket wood stove to heat my 160 sq ft tiny house and have it ready for winter. I don't know if I will have it finish by then, at least I will have heat to work on it. I was hoping for some input on the design before I build it. Thank You!

with no mass the rocket design may not be your best choice, do you have the book?

I hope to extract most of the heat from the stove with a pot of water, Water distiller, cooking food, lava rocks, bricks, computer cpu heat sinks and sterling powered fan, from the top of drum.

You might want to up the diameter of the pipe to 6."  You might get the 4" to work, but there has been problems with that small of pipe.

I like your design.







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I think I would go with the pocket rocket design from the rocket mass heaters book and sink the bottom half of it into a tub of water or other thermal mass, then I would add a door and a damper so that the pocket rocket could be sealed up when the mass was warm to conserve fuel. the real advantage of the rocket mass design is that it allows for running the exhaust through a large thermal mass extracting most of the heat that would go up the chimney being on wheels you can't pack the ton or more of thermal mass.

also the pocket rocket design is very scalable unlike the rocket mass heater which seems to only work well with 6" or bigger exhaust duct

I think I'd like to see this built, and see how well it works -- also, whether it would be safe to run in such a small dwelling.  I've been trying to figure out what to do for a similar situation (considering taking a 24'-28' cargo trailer or enclosed car hauler trailer and turning it into living quarters for DD and myself until we can build a house).  I wouldn't use water for the mass unless you have it well-enclosed (would slop out if you moved the trailer), and if you have it well enclosed, you'd need steam vents on it.  Would be easier to set the whole construction in a container of cement that was bolted to the floor before the cement was added. 

Kathleen

I wouldn't use galvanized steel.  It's possible to get this puppy hot enough to vaporize the zinc.

And if you build this too close to the kitchen utensils and they are also galvanized, then you'd have everything including the kitchen zinc.

Size and weight are major factors in my design to use in my tiny house. 6" pipe I believe would be great in a 55 gallon drum version. I hope to extract most of the heat at the top of the drum and have a fairly cool exhaust gases to vent. I believe I can over come the any potential 4" venting problems with the quick and efficient venting of the exhaust gases. All the galvanized steel could be replaced with either blued or black pipe and fittings at a increased cost. If this design could be made workable and efficient, I would recommend all stainless steel version including the drum but at a much increased cost.

If you could change that first 'elbow' for something more like an 'L', with a sharper corner, I think it would increase the turbulence, mix the air better, and produce a better burn. 

How about 4" stainless steel exhaust tube custom wielded to replace burn chamber and riser tube. With the added cost of the 4" 304 stainless steel Saf-t Liner tee needed to replace the 4" 304 stainless steel 90, a custom wielded stainless steel tube might be a better option, more efficient and last a lot longer. Thank you I will be looking in that direction. 

Sounds good to me!  But I should point out that I have no first hand experience, anything I know is just theory from what I've read. 

I hadn't heard of "rocket stove" before,  but I see what it is.  I don't think it's practical for heating.  for one thing constant feeding with a consistent fuel size may be an issue.  Ok for cooking where it will get constant attention.  I built a wood gas unit big enough to power a 360 gas engine,  but didn't use it much because it took too much time to process the wood.

I have lived in an 8x14 cabin for several years,  with a little ordinary wood stove in the corner.    Last year I moved in an old motor home with missing engine and very leaky roof,  built a roof over it,  stripped out all the water damaged interior which was all of the stuff on the front half,  kitchen and dining area.  Put in a block base for a stove and a quickly made wood stove out of a hot water heater tank.  chimney went through the old gas refrigerator metal access door.  Been cooking on it all winter.    The rest of the open space became my electronics experimenting shop.  Of course I live on 80 acres way out in the middle of 1000's of acres timber company land.  A little smoke won't bother anyone and fuel is plentiful.  I love land and don't care if my house is small,  since I work outside during daylight hours anyway.  If I had fuel shortage or neighbor/smoke issues I might want a more efficient stove.  Then a little water stove might be good, a  fast low smoke fire once a day and then the hot water keeps me warm the rest of the time.  An old gas water heater might do the job there.      Everything torn off of it and the tank set on top a  little fire box with a chimney out the top.  Would have to allow for easy removal of the chimney to scrape the creosote down from the tube inside frequently.  always use it in open top mode,  just keep it full of water.  The uninsulated tank full of hot water might be enough to keep warm,  if more is needed add a little tiny pump and radiator with fan.  If less is needed,  slap some insulation on one side of the tank.

I was going to build a rocket stove in my mobile home and decided to keep on using my 30 gallon steel drum Volgelzang "air tight."  I lined the drum with fire brick and it turned out to be a really nice stove.  I collect throw away pallets for fire wood.  So far I have been making it through the winter disassembling about 150 pallets that were on the way to the landfill. The good ones are made from Oak.  By the end of March I had to fire up my Britelyte "howler" a couple of times because we had a long cold Spring and I ran out of wood.  My stove works really well though.  I changed my mind about a mass heater in my mobile home because of the space it takes for the mass.  I wasn't worried about the weight though.  In a micro-home on wheels it would make plenty of difference though.  You will need a really efficient heat sink for saving that heat.  Water works well but........ It sure does present some interesting challenges.

I am hoping with my tiny house being well insulated (R15 walls, R24 ceiling, with foil facing inside and 1/2" air space between foil and interior siding) it shouldn't be to hard to heat. I have already a noticeable heat gain in the the building with just incandescent light bulbs burning. A rocket stove design without a major heat sink should provide heat quicker from a cold start then a regular wood stove with the disadvantage of a short burn time unattended. With a J tube type feed, longer wood can be used to increase burn time to a point. Maybe a corn or pellet stove fuel feeder could be used to extend burn time. I am hoping with this design or something similar to work out the bugs and provide the needed heat for my well insulated tiny house, maybe a 30 minute burn every 4 to 6 hours in extreme cold weather. It seams to me this design or a 55 gallon version with a 6" burn tube would make a good work shop heater, heats up quick, uses minimum fuel for the heat output and a quick and safe shut down when heat is no longer needed.

I hope that it is effective.  I am considering a rocket stove heater for my tiny home but that isn't going to happen this year.  Hopefully next year though.

Work on the new rocket wood stove is near complete. Picked up the last needed parts last Tuesday at my local heating supplier. I have dropped about 100 bucks so far, but it really seams to be worth it! Construction took a better part of three afternoons with lots of deliberations and revelations. The 16 gal grease can I got had seen better days, even dented and out of round, it was made to work. I replaced the wood combustion chamber 90 degree elbow with a tee and cap for hopefully a better burn and larger combustion chamber. Attaching the combustion chamber and and riser assembly to the inside of the barrel turned out to be a little tricky. I used a flexible sheet metal L bracket and screwed the combustion chamber to it. Also cutting the combustion chamber heat shield to fit the outside of the barrel turned out to be very time consuming and far from perfect, but it works. The first test seemed to be a success. Lighting the stove without smoke back is a trick I will have to learn. Once stove was lite with fuel under riser, stove heated up fast and burned clean. The only problem seems to be the feed tube is too far away from where the fuel needs to be. I am going to use another 90 degree elbow in top of feed tube to better direct the fuel under the riser and hopefully get less smoke back. Stove works very well feeding fuel though clean out opening. Using a IR temperature tester I read over 800 degrees at the center of the top of the stove and about 140 to 250 degrees at the exhaust tube. The upper side of the exhaust chamber exterior of the drum was anywhere from 500 to 600 degrees at the top to 250 to 350 degrees at the bottom. Below exhaust chamber the exterior of the drum was 180 to 85 degrees. The exhaust fitting on the side of the drum was about 350 degrees. I used 450 degree silicon the seal the fitting to the side of the drum, so that worked out well! Other then the feed tube difficultly which I hope to fix tomorrow, The stove works great! I will be running more tests in the coming days and will post a updated diagram/material list soon with more pictures.

More pictures.

More pictures.

More pictures.

More pictures.

Last picture for now.

I hope to continue testing the capabilities of the stove in a week or two. I am planning to fill the top of the stove with sand or small stones and bury the bottom of a pot in the sand and run some boiling water time trials as my first test. I am open to new ideas or suggestions for any further tests. I have updated the diagram/material list as built, so enjoy.

New feed tube installed and painting completed.

Hermit, what an awesome job you did! I have a question and a suggestion for you. The question is what specifically did you paint it with? i.e. product & brand. The suggestion is to put a shelf on the feed tube with at minimum 1/3 of the tube at the bottom for a cold air feed. I think that will help with convection & ultimately with smoke back! Excellent job! Great pictures too! They are very helpful! Thanks!

The paint I used is Rutland, fast drying, flat black, high temp, 1200 degree, stove paint in a 16 oz spray can, that I bought at home depot for about 12 dollars. I am hoping I can use the clean out as a combustion air entrance and cap the feeder tube after fuel is loaded. I only hope that the fuel burns off on the end and slowly feeds down the tube instead of all the fuel catching fire and burning in the feeder tube and getting smoke back out the seams of the feeder tube. I believe there is a trick there and I will find it! If I end up using the clean out tube as the feed tube then I try inserting a shelf in the clean out for a combustion air entrance. I will also be monitoring the exhaust vent pipe temperature very closely as I made my own roof thimble and will be using single wall pipe though the roof in the Hermit DeLuxe. I don't want the exhaust vent pipe much beyond 160 degrees. It just been too warm around here to fire it up and work around it, but I will find the a time soon.

Fired up the rocket wood stove yesterday and ran it for about 2 1/2 hours. I didn't try to use the feed pipe for this test. I had a little smoke from the fresh paint for a few minutes and then gone. I put a large canning pot and lid with about a gallon of ambient temp rain water on the stove top at the start and after 2 hours or so the water was about 150 to 160 degrees. Great for washing the dishes! I was barbecuing dinner at the time and wanted just to heat up and run the stove to see if there was any apparent problems. The stove worked well, using the fresh air intake as the fuel input. I had a typical rocket stove running experience. During lighting or full operation I had no smoke back and when up to temperature, clean exhaust! Fuel burnt complete to coals and coals stayed hot enough to lite new fuel for about 30 minutes before turning to ash. All in all operation was clean, safe and smoke free with a minimum of my attention. I will be using some sand blasting sand on the top of the stove to put the pot in for the next stove run up. I hope to boil the water next time.

S00per c00L

Sweet........ Can't wait for your next post.

    I have finalized the rocket wood stove installation into the Hermit DeLuxe my 160 sq ft tiny house on wheels. I installed 26 gauge galvanized sheet metal mounted 1" from combustibles  for heat shields under the stove and on the wall next to the stove. Since I used 1/2" emt pipe for legs of the stove, I used 1/2" emt set screw connecters mounted in bottom heat shield to firmly mount the stove in place. I used single wall 4" blued wood stove vent piping from the stove to the 4 ft long 4" double wall gas vent pipe going though my custom 4" roof thimble ,sheet metal roof and roof flashing with a 4" gas vent cap for venting the exhaust gases. I also added additional heat shielding for the vent pipes using 4" blued pipe and 3/4" 10/32 bolts and nuts to obtain 3/4" spacing between shield and vent. I sealed all seams with high temp silicon and painted stove, vent pipe and heat shields with high temp black spray paint. I added a shelf in the fresh air intake to improve combustion.
    I have found I need build a base of red hot coals under the riser tube with easy quick to burn softwood before I start using hard wood. For this test I used the fresh air intake/clean out to fuel the rocket stove. Fuel had to be moved forward every couple minutes to keep the rocket stove firing as in any horizontal      feed rocket stove. Once the stove was up to temp 800F+ top center of drum, loaded with hardwood burning hot and loud, the new paint started smoking and smoked for 10 - 15 minutes before finally curing. I used a box fan in a window to clear the smoke out of the hermit as it was being made and it cleared quickly after the stove stopped smoking. The hermit was about 47f when I started firing the stove, six hours later the hermit 65f to 70f everywhere. I had to restart the stove two times and install new shelf with air holes by removing the burning fuel and coals and installing the shelf quick as the fuel was putting woodsmoke in the hermit and putting the fuel back in. Glad I had a box fan in the window. At near to the end of the day I installed a adjustable fan on a rotating base to the ceiling next to a switched outlet to move air over the stove and hopefully balance out the air temp in the room. In the last hour I poured clean dry playground sand in the top of the rocket wood stove and leveled. The sand was about 47f when I put it in and about 118f right before I left, on a stove I had left the fire to die and the stove to cool off. I will have a post tomorrow night with my results and conclusions. 

  Results: I believe the rocket stove as installed is a mild success. It seams to work safety, near by walls, floor and ceiling were 90f or below at any time during the test. No smoke back and draft occurred almost instantly when starting stove. Stove was easy to start but though operator error flamed out twice for the lack of easy to burn softwood and my hardwood fuel was somewhat wet. Once the stove was up to temp and full of hot burning hardwood the exhaust was smokeless and the room started to heat up nicely. Being it was only mid 40f outside I wonder if there is enough btu output to heat the hermit at 10f or colder? Also the exhaust vent pipes temps where anywhere from 160f to 230f, higher then I wanted
    Conclusions: I believe I can make the stove work as installed with continued improvements. I am hoping using the sand with a pot of water on top of the stove will bring down the exhaust vent pipe temps. Also the design is flawed the vertical fuel feed tube is to far away from the combustion chamber under the riser.  I will be working on a custom wielded steel combustion chamber/riser tube with 60 degree angle feeder tube into the combustion chamber. In the mean time I will be working on using the existing feed tube to fuel the stove and make it work for longer burn times unaided. I will continue to heat the hermit with the rocket stove as needed to finish the hermit over the winter using the wood scraps as I go and so that is the success. I will continue to update this post as any progress is made. Thank You

I wonder if lengthening the exhaust pipe inside would allow you to extract more heat plus lower the exhaust temp.  Nice install job by the way.

Hermit DeLuxe wrote:
    Conclusions: I believe I can make the stove work as installed with continued improvements. I am hoping using the sand with a pot of water on top of the stove will bring down the exhaust vent pipe temps. Also the design is flawed the vertical fuel feed tube is to far away from the combustion chamber under the riser.  I will be working on a custom wielded steel combustion chamber/riser tube with 60 degree angle feeder tube into the combustion chamber. In the mean time I will be working on using the existing feed tube to fuel the stove and make it work for longer burn times unaided. I will continue to heat the hermit with the rocket stove as needed to finish the hermit over the winter using the wood scraps as I go and so that is the success. I will continue to update this post as any progress is made. Thank You

You may want to look at the thread I started about my heater. It has some similarities to this one, but is 6inch and therefore bigger. I used a water heater core for mine and so it is heavier.

https://permies.com/permaculture-forums/10653_0/alternative-energy/yet-another-portable-rmh

I wanted to be able to leave the fueling for long times as well and so have a cartridge system for that. The cartridge tries to be air tight and I use a separate air intake that I will be keeping at only 1/4 CSA intake. I found adding secondary air really helped get a hotter heater and no visible smoke. I am putting bricks around mine that will add about 450lb... this may or not be an option for this one.

One thing that may work as mass without being too heavy is tin. Tin has a low melting point and could store more heat for less space and weight because of phase change. It has been used in some solar cooker designs for cooking after dark with success.

Dave, I have heard the best height of the riser is about 36", my barrel just isn't tall enough. It's seems Len's hot water tank rocket stove design is better suited for a longer riser. Len, I heard the basic rocket stove design is similar to ancient wood fired pottery kiln design. The kiln had fresh air pumped in with hand bellows into the base of the riser just above the combustion chamber to increase temperatures in the kiln. My thought is to have a couple 1/2" to 3/4" pipes from the base of the riser above combustion chamber to the outside of the stove angled down so smoke will not come out. The pipes could supply fresh air at the base of the wood gas fire in the riser and increase combustion temperatures.The combustion gases flowing by the end of the pipes should draw fresh air into the riser not requiring any additional energy to move the air. Just a idea!

Hermit DeLuxe wrote:
Len, I heard the basic rocket stove design is similar to ancient wood fired pottery kiln design.

proto kiln I think are called.

The kiln had fresh air pumped in with hand bellows into the base of the riser just above the combustion chamber to increase temperatures in the kiln. My thought is to have a couple 1/2" to 3/4" pipes from the base of the riser above combustion chamber to the outside of the stove angled down so smoke will not come out. The pipes could supply fresh air at the base of the wood gas fire in the riser and increase combustion temperatures.The combustion gases flowing by the end of the pipes should draw fresh air into the riser not requiring any additional energy to move the air. Just a idea!

Thats what I am finding. I am running an air space through the burn tunnel so the fire preheats the secondary air. I did use a pipe in the first trial which worked great. Next I tried a bend piece of tin but got the air spaces too high up on the sides of the burn tunnel which interfered with the primary burn. I am going to try another plate with all the secondary air (reminds me of "Londonderry air" something  I was tortured with in music lessons) at the bottom... sort of m shaped (not M shaped).

Muzhik wrote:
I wouldn't use galvanized steel.  It's possible to get this puppy hot enough to vaporize the zinc.

And if you build this too close to the kitchen utensils and they are also galvanized, then you'd have everything including the kitchen zinc.

The real issue is not that zinc will deposit on other metals it is that zinc fumes are poisonous.
https://secure.wikimedia.org/wikipedia/en/wiki/Metal_fume_fever
http://www.nlm.nih.gov/medlineplus/ency/article/002570.htm
In severe cases, far worse than what you would have in this case, deaths have occurred.
http://www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo

hepaestus wrote:
The real issue is not that zinc will deposit on other metals it is that zinc fumes are poisonous.
https://secure.wikimedia.org/wikipedia/en/wiki/Metal_fume_fever
http://www.nlm.nih.gov/medlineplus/ency/article/002570.htm
In severe cases, far worse than what you would have in this case, deaths have occurred.
http://www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo

I agree.  Every wood stove I ever built out an old water heater was cut open and heavily fired outdoors until there was no trace of zinc left anywhere. 

I hope the fumes from the galvanized piping and fittings have already gone up the exhaust vent and are gone. All other external galvanized parts are painted with high temp paint and shouldn't cause any problems. 

Hermit DeLuxe wrote:
I hope the fumes from the galvanized piping and fittings have already gone up the exhaust vent and are gone. All other external galvanized parts are painted with high temp paint and shouldn't cause any problems. 

Me too for your sake.

I recently updated the stove, seems to work better.

Dave Bennett wrote:

hepaestus wrote:
The real issue is not that zinc will deposit on other metals it is that zinc fumes are poisonous.
https://secure.wikimedia.org/wikipedia/en/wiki/Metal_fume_fever
http://www.nlm.nih.gov/medlineplus/ency/article/002570.htm
In severe cases, far worse than what you would have in this case, deaths have occurred.
http://www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo

I agree.  Every wood stove I ever built out an old water heater was cut open and heavily fired outdoors until there was no trace of zinc left anywhere. 

I have enjoyed reading your site and the information and ideas you present, but it bothers me to see this forum allows postings and images that can get people injured or killed. Many of the chimney pipe I have seen used with the rocket stove installations appear to be galvanized (HVAC) and can vaporize the zinc coating at the temperatures it is subjected to by the fire. When zinc is vaporized from hot stove pipe, the pipe takes on a frosted appearance. This is just one reason NOT to use HVAC duct as a chimney for a stove. Zinc can vaporize from brass and brazing rod when it gets too hot. It can vaporize from galvanized pipe or other galvanized metals when they are heated or welded. Zinc is very useful as a coating to prevent rust, but can be extremely dangerous when mishandled.

Your first two references are good basie information but the reference #3 to anvilfire bothers me as it was written by a person that is dead. Since the first posting it has been added to several times, presumably by the same dead person. Another reference to Mr. Wilson's death and several references to zinc fumes can be found at http://www.iforgeiron.com/topic/23962-zinc-questions-read-this-first/page__hl__galvanized__fromsearch__1 .

Check the inside of the chimney and is it as clean as the day it was installed or is there a coating of something on the inside? Creosote is a byproduct of incomplete combustion that occurs in a rocket stove at the start of each new fire. With thin wall pipe that I see being used on many of the rocket stove images and videos, what provisions are made to replace the pipe once it starts to rust and or collapses?

With any wood fire there will be ash as a byproduct. Ash is hygroscopic, tending to absorb moisture from the air, and can cause rusting. What provisions are made for a clean out to remove that build up of ash that will build up over time?

We heat with wood and I am very interested in building a rocket stove, but only if it can be used safely without the fear of injuring my family and if it can be maintained with out being rebuilt when something needs replaced.