Rocket stove slide allows for burning of 6 foot long firewood

      I'm not a big fan of handling millions of pieces of little firewood so I plan to cut most of the wood for my rocket stove in long lengths up to 6 feet.

     I have a large resource of maple coppice and 3 to 6 inch alder which needs to be thinned. Much of the alder is dying so in mid summer these thin trees are dry and ready to burn. Living trees which are cut in mid summer while in full leaf dry out very quickly when cut and left with their branches on so that the leaves continue to transpire.

    The plan is to build a U-shaped sheet metal slide which is set about 10° from vertical so that long lengths of firewood will lay straight and automatically feed into the rocket stove. I've chosen the U-shape so that there are no corners for material to catch on and so that nothing falls off the slide. A slide is preferable to a tube because it does not require extreme ceiling height. A 6 foot tube would require a 12 foot ceiling. Even if there was room it would still be awkward to lift material to this height and then lower it to the burn tube. Also with a slide you can see what's going on all the time. With a feed tube it's quite likely that a clog would go undetected which would result in the fire going out.

   The primary reason for going with long lengths is so that I don't have to handle many little chunks of wood but there are other efficiencies as well. When poles are loaded onto a truck they can be stacked so that they protrude just beyond the tailgate as this expedites the unloading process since you never have to climb onto the back of the truck. Rather than stacking the firewood horizontally they can be stood in racks so that it's not necessary to bend over when hauling wood into the house or when feeding the stove. I'll turn an old wheelbarrow into a mini stake truck so a big load of poles can be brought in efficiently and the firewood door will be 3 feet wide. Racks adjacent to the stove will allow these poles to be stored neatly.

    Of course there will be times when I need short pieces of kindling and not every tree lends itself to being cut into nice uniform poles. This short wood will only be handled once. In the course of doing my business I inherit plenty of unwanted garbage cans and boxes. Short firewood and kindling can be loaded into these containers when the material is cut and then all the boxes and cans will be stacked for later use and none of the wood will be handled individually until the containers are brought into the house and they are fed into the stove.

    Does anyone have other ideas on how to reduce the labor associated with cutting, gathering, stacking and finally burning firewood?

I will curious to see how your feed slide works. I read that you can't make to feed tube too high of it can back draft, but having an open slide should not do that. The biggest thing I could imaging going wrong was if the fire burned up your slide. To make cutting and splitting easier for me, I cut 8" pieces to load in the truck and then cut and split where I stack it. I think this is easier than doing it in the woods. I have everything I need in one cleared out space. That and I load fewer pieces into the truck and then just stack the multitude of cut and split pieces once near the furnace. I am building a RMH this winter in a greenhouse and like the idea of using the branches, and smaller trees there. I thought it was interesting you have coppiced maple. I need to clear several maples that have shaded out a few apple trees. coppicing would be a good way to give the apples some day light and get some firewood.
kent

I just read something recently about a feed tube for a rocket stove resulting in the stove burning much too hot, warping metal components, etc. Sorry I can't find the link again. If I recall, that was more to do with a constant supply of fuel than the tube itself.

Hi guys, well just thought about this yesterday. I had an idea, why not put a tube above the feed tube, with four legs, to hold it above the feed tube? The space between magazine tube, and the feed tube should be made two three times the inlet surface, and the magazine tube should be smaller than the feed tube, so wood doesn't bind. And should be made removable obviously to start the fire etc.

    If a tube is used there is a real danger of it turning into a chimney. If the fire moves up the wood it's possible that a tube would create enough draft that the airflow would travel up the pipe and quickly fill the home with smoke. An open slide cannot develop its own draw and it would not interfere with airflow into the burn tube.

    Supposing that this very real danger did not exist a vertical tube would still be a poor choice since materials are more likely to clog when they don't know which way to lay. In using slides for demolition debris I have found that vertical chutes are much more likely to clog than those on a slight incline. Materials on a slide tend to line up nicely with their length parallel to the sides of the slide.

  Try this experiment. Stand a garbage can up in the normal manner and fill it with broomstick sized twigs. Then drop another can on an 80° angle and load the same material. The can on the incline will have a nice neat stack of wood which lays against the side. The can which is stood up vertically will have a wonky load which crisscrosses all over the place. The crisscrossed pile is much more likely to clog.

  And then there's the reason I chose a slide to begin with. The material can simply be set onto the slide and does not have to be lifted to the top and then lowered down. This allows for the burning of quite long material without constantly banging the ceiling while trying to load long materials.

  The coppiced maples are a happy accident. They were cut when the place was logged and have refused to die. One Maple was cut off at about 5 feet from the ground has about 40 coppice trunks 35 feet tall and as big around as my leg seven years later.

dale hodgins wrote:
    If a tube is used there is a real danger of it turning into a chimney. If the fire moves up the wood it's possible that a tube would create enough draft that the airflow would travel up the pipe and quickly fill the home with smoke. An open slide cannot develop its own draw and it would not interfere with airflow into the burn tube.

Pardon me, I misread your initial post. I thought by "slide" you were saying "incline" rather than a vertical feed tube. Didn't comprehend that it was an open shape as well as inclined.

Dale, glad to hear about the maples. Most of our wood lot is covered with maples and I need to thin some out. The crowns are so thick that on a sunny day it is dark and damp while walking around. Maples are the predomenent new growth on our place in the woods, but out in the pasture it is black locus and sumacs.

This is exactly what i've been thinking about.

Something else to note about the design. It wouldn't really matter if you loaded 1 6ft piece of lumber into the slide 2 3ft or 6 1ft, they'd still slide in and burn right up all the same. Also, as long as your slide is slightly narrower than the feed hole you shouldn't have to worry about any pieces catching as they feed in nor any knots catching.

  I think piling various length material on top of one another in the slide may be dangerous since there's a possibility of the upper piece kicking the lower piece out sideways once it's burnt down and not very heavy. Often when wood settles as it burns it doesn't do so completely evenly but rather does it in little jerks. Because of this danger I will install a wide ring made from 18 inches of a 45 gallon drum at the bottom of the slide and encircling the feed tube to prevent a kicked out piece from going anywhere. When I am feeding several long pieces at once I'll put them side by side and they can feed in together.

    I don't envision burning 6 foot plus material all of the time but the long stuff would be very handy since it allows you to ignore the stove for a time. So a couple long skinny chunks would be just enough to keep the stove burning and at any time the operator can add shorter firewood and odd shaped pieces directly to the feed tube to ramp up the fire.

    Several rocket stoves will be needed for various greenhouses, hot tubs and an outdoor spa and I will thoroughly test the slide in these applications before installing one inside the living space.

Not having read the whole thread here, I had a similar thought about feeding some kind of fireplace/stove/whatever using a large pice of scrap pipe (about 12-23 in. diameter). The design problem I run into is that the fire/heat from the stove/etc would want to continue burning the wood right up the slide/ramp/etc.
It would be tricky to keep that from happening.
I will come back to this thread to read the replies and see if that problem has already been addressed.

    I think we've established that a pipe could become a chimney which sucks in the wrong direction.

  An open slide can't develop the chimney effect. So the main issue becomes, how do you avoid clogging the slide? How do we prevent wood from being kicked away from the slide?  Any sort of ring for this purpose would be unacceptable because it defeats the idea of easily loading the slide.

Ok.... I'll give.....

The feed "slide" needs to be a tube; The tube must be horizontal; and for best effect, either the tube must be sealed at the other end, or the other end must be used as a draft control for incoming air.
This way, as far as the burning is concerned, it will work.
The problem of course is how to feed to wood.

It may be possible to have a large, gentle curve going from an incline to the actual feed portion, which would be horizontal, and/or to use the weight of the wood on the incline portion of the curve to push the wood along, possibly through simple mechanical means, as opposed to trying to rely on weight/gravity.

Not entirely true, look up the Kings Cross subway fire where an escalator, an inclined open 1/2 tube, became a chimney. Less likely yes, impossible no!

Dale Hodgins wrote:    An open slide can't develop the chimney effect.

I read up on the fire.

The escalator itself was on fire being made partially of wood and having been operated for fourty years without all the grease being cleaned up. The escalator didn't channel the fire. It was the fire. I've dealt with brand-new escalators and even they contain buckets of grease

I won't use wood or grease in the construction of my slide. I think metal would be a more appropriate material.

The fire engulfed not only the upper surface but the hidden portion which only the technicians see. A 12 mile-per-hour wind assisted this fire.

All of this makes for a poor example of how an open slide could possibly cause a chimney effect. If suddenly there were a strong wind coming from the J tube I suppose the slide would be engulfed. Short of that, I just don't see it happening.

A search around the Internet failed to produce any evidence that an inclined surface could become a chimney.

But just to be extra sure, I'll set up a slide outside and get a fire going at the bottom of it. My expectation is that the heat and smoke will go straight up and will have no reason to follow the plane of the metal. For it to do that there would need to be some force at work making it do that. I believe that in windless conditions the smoke would simply follow the path of least resistance and go straight up.

Try line 7, page 12 of the following. they call it the trench effect.

http://tinyurl.com/bp8sega

I really like this idea. Took an image from the web and modded it as an idea. The feed guide is not a solid tube, but rather an open metal frame. There is a small plate weled to the bottom to only allow one stick at a time to enter the stove. Gravity should feed the stick in as it burns. Once the stick on the bottom is burned a new one should drop in place. I use a similar method for storing/organizing wooden dowels in my shop. It works well for dowels of different lengths and diameters.

Potential issues:

If there is too much friction between the bottom log and the guide it won't slide in via gravity.
Having too much wood loaded into the guide would increase the weight on the bottom stick and increase the friction.
Mixing lengths of wood could cause binding issues, stacking with longest on the bottom would probably negate this.

Other considerations:

Increasing the angle of the guide would decrease the friction with the guide and would allow the stick to slide in via gravity easier.
If the guide angle is too steep you run the risk of the log catching fire outside of the burn area, as you already mentioned.


I think your on the right track with the feeding of one long stick for a long burn, seems like it will be easier to autoload one or two long sticks than a dozen short ones.

:Edit: Added another image of a possible profile view of the log feeder. Left is single stack, right is double stack similar to bullets in a magazine.

Regarding the post directly above – I'd like to see a video of how this thing works. I'm not sure if long poles of twisty firewood would fit into that contraption which holds dowels. Much of my long material will be curved and rough branch material. ---- I won't be trying anything complex. No moving parts equals nothing to break down. I'm going to go as close to vertical as I find practical. No plans to stack very much if anything on top of one another. I could see sending several pieces down side-by-side but I think stacking them would create problems. I have some sheet-metal at the property so I could easily do a quick outdoor mockup and try the slide on various angles and with various types of wood. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- regarding earlier posting------

Well according to that "it can be done." I was unable to determine whether they had a ceiling which was on the same plane as the escalator. If so, this would contribute to a chimney effect. If on the other hand it was a big cavernous building with a horizontal ceiling far above then that wouldn't have much effect. I still think the most important part of that story is that it was a wood and grease fire. The escalator itself was burning.

I've said that I plan to use a U-shaped slide. The font available doesn't show the actual shape. It will comprise no more than one quarter of a complete tube – 90° on the protractor. The higher the sides, the more likely it would contribute to airflow issues. I also plan to end the slide about 1 foot above the J tube. The last little chunk of each log will drop to the fire independently of the slide. A half barrel ring will prevent anything that bounces from escaping into the room.

My plan is to run only a couple of sticks at a time down the slide. If they were piled a dozen deep, then any flattish boards or other wood on top could effectively become a lid which would turn the slide into a chimney.

I did a simple burn test using the cardboard cores from paper towel rolls. The one cut in a shallow trough form burn slower than the one left cylindrical. Of course it needs to be tested on nonflammable material.

The need for constant tending and inability to burn long chunks of wood are the only non-user-friendly issues I have with rocket mass heaters. I haven't heard of anyone burning large diameter material. For a large unit heating a big home or commercial space it would be nice to not have to split everything into toothpick sizes.

Does anyone know if a heater has been built to accommodate large dimension firewood?

I've already gathered some of the materials necessary for this contraption and the first one will be built in my greenhouse/flophouse. Only after a successful season in the greenhouse will I go to the trouble of building an attractive stainless steel version to feed the main heater inside the house.

1/4 tube should be good, part of the Kings Cross problem was the vertical walls of the escalator. The slide angle will be important since too low an angle will loose the self feed of a vertical chamber. The "dowel feed" shown a post previous wouldn't be good. As you pointed out there would be a chimney effect and unlike nicely round dowel, the nubs of branches would almost guarantee binding. A steep angle, 75 degrees or thereabout as a guess, with a shallow support trough would likely work well. Good idea.

I'll take some video when I do burn tests at various angles.

Another totally separate feeding device will be used by my bed in the greenhouse but I would never try it in the main house. I will mount a short length of pipe by my bunk bed so that I can send short chunks of wood airmail to the feeding tube. This pipe would be 18 inches from the fire. It would not store any material. This will be a totally redundant system installed primarily so I can document the results. I expect to spend no more than half an hour hanging a pipe from the ceiling on the right angle to accomplish this.

The impact of a piece being shot into the fire has a distinct danger to it since smaller pieces could be flipped right out of the fire upon impact. Anyone who has ever stacked loose wood or scrap metal has seen this happen. You throw something onto the pile and the force of the impact launches a smaller piece into the air. That's well I'll only do this in the greenhouse as a means of avoiding getting out of my warm bed to feed the fire. No need to tell me the dangers on this one. I've just stated them. I've successfully fed many fires from the comfort of my bed at demolition sites. Never cought the blankets on fire but that was certainly within the realm of possibility.

Dale Hodgins wrote:Regarding the post directly above – I'd like to see a video of how this thing works. I'm not sure if long poles of twisty firewood would fit into that contraption which holds dowels. Much of my long material will be curved and rough branch material.

Sorry no video as it's just an idea I had. Long poles of twisty fire wood would most definetly not fit into my dowel holder, it's 4" PVC, but is a similar idea. Basically just a chute, slide, guide, channel to hold / guide the stick into the feed area with a stopper to only allow to bottom piece to enter. I guess if your using 6' long sticks you probably wouldn't even need to stack them anyway. I have a log rack in my wood burning stove that is similar to this idea. It's like a standard rack but at an angle leading to the back of the stove. You stack wood on it 2-3 rows high and as the bottom back log burns the fastest it turns to coals and the rest of them shlump down to the next spot. This lets me load it up once, once the coal bed is established, then leave it for 4-8 hours without needing to tend it.

mekennedy1313 McCoy wrote: As you pointed out there would be a chimney effect and unlike nicely round dowel, the nubs of branches would almost guarantee binding.

Why would their be a chimney effect?

I agree rough or not uniform branches or sticks would not stack well, but if the branch was long enough there would be no need to stack them. I guess I assumed since the wood was from a coppice it would be semi uniform, but you know what they say about assumptions...

Ok my ms paint pics suck so I made it in Sketchup real quick. I think this is the idea you are describing Dale, or atleast what I envisioned when I was thinking of it. The idea I had earlier about stacking probably isn't the best or necessary. I could see trying to make an auto feeder or loader if you had to use many small sticks but since we are talking about using long sticks I think they would both accomplish the same thing.

In the pic below the log is 8" in diameter and 6' long. The RMH shell was just a quick sketch of the usual shape so not really to scale. The angle of the wood is at 45 deg. I would think trial and error wouldn't take long to get the angle adjusted correctly.

Thoughts on the angle:
A stepper angle is going to put the fire more directly under the feed opening, which could lead to the fire climbing back up the log. Though with the draft of the RMH it might not matter.

A shallower angle would move the fire further into the RHM and perhaps even far enough to not be directly under the feed opening. Too shallow of an angle and the wood might not slide down and autofeed itself.

This is what I was trying to describe about the angle. The steep one is at a 70 deg angle, the shallow one is 30 deg, with respect to the horizontal. These are exagerated angles to help illustrate what I was describing, not suggesting they be at these angles need real trial and error for that.

Hi, I'll say right up front that I'm probably the least experienced on this thread, but I've been doing lots of research prepping for my RMH. Page 54 of Ianto Evans RMH book says that something as simple as the sticks catching on each as they stick up through the intake can cause a chimney effect. So, even an open slide would be suseptable, I would think.

I'm with you Dale, I'm trying to figure out a way to not have to sit full time near the stove and feed it. Even Mr. Evans admitted in his book that this is a drawback to a RMH.

Maybe part of focus needs to be on the exhaust rather than the input, to ensure that the actual chimney is so strong it will pretty much always overtake any tendency for the intake to back up (I hope that makes sense).

Brad's last drawing comes closest to what I envision. The edges would be tipped up a couple inches to prevent material from escaping.

Regarding Sandra's draft concerns.------ I intend to send my exhaust through a chimney that is somewhat higher than normal in order to create draft. In the summer I'll attach it to a tall black stack which will heat in the sun and turn the heater into an exhaust fan on hot days. Sometimes I'll create draft at night so that the thermal mass can cool down and become a heat sink during the day.

I think much of the problem with initial draft is that heaters are allowed to get too cold between uses. If a new fire was run before the unit completely cools, it should be easier to start the airflow in the right direction.--------- My heater will be part of a Trombe wall complex so I will often find it is already warm when it's time for a fire. This should allow me to open the damper and immediately begin airflow.

Sandra Ellane wrote: Ianto Evans RMH book says that something as simple as the sticks catching on each as they stick up through the intake can cause a chimney effect. So, even an open slide would be suseptable, I would think.

That makes perfect sense. I was wondering how a bundle of sticks could create a chimney effect, but I think I got it now.

Dale Hodgins wrote:
Regarding Sandra's draft concerns.------ I intend to send my exhaust through a chimney that is somewhat higher than normal in order to create draft. In the summer I'll attach it to a tall black stack which will heat in the sun and turn the heater into an exhaust fan on hot days. Sometimes I'll create draft at night so that the thermal mass can cool down and become a heat sink during the day.

That is an awesome idea! Basically using the exhaust of the RMH as a solar chimney. I would bet that having a flat black exhaust tube that gets sun would create the heat needed to create and up draft on its own.

Hi Brad. A few months ago I posted my plan for turning a rocket mass heater into an air conditioner and dehumidifier. I will now attempt to cut and paste that information here.---------------------------------------------------------------------------------------------------------------------------------
Rocket mass heater converts to cooler/air conditioner Dale Hodgins 353 views Monday, August 08, 2011 12:53:17 PM by Dale Hodgins
--------------------------------------------------------------------------------------------------------------------------------------------------------- . If you scroll back to the postings of August 8 I describe the plan. Your photo of the earth tube looks like one of the options. I may run a tube through the cold water of a shaded pond on the north side of the house .------------------- I was surprised to find that no one was interested in doing this. It would seem that in southerly locations the air-conditioning and exhaust fan options might be used more than the heating function.

Your photo of the stacked logs illustrates why I don't want to pile things too deeply on a slide. In my case it would be very easy to accidentally create a chimney since I am likely to burn plenty of milled lumber which would naturally create an air seal between various chunks on occasion. But laying side-by-side the same wood is unlikely to create a chimney.

Brad, I wonder if I could get you to post that last photo onto the thread mentioned above? After that is done I'll explain a couple of different ways to alter that system for various purposes. Thank you in advance. I'll post on that now to bring it to the top of the list.

Sandra Ellane wrote:I'm with you Dale, I'm trying to figure out a way to not have to sit full time near the stove and feed it. Even Mr. Evans admitted in his book that this is a drawback to a RMH.

Maybe part of focus needs to be on the exhaust rather than the input, to ensure that the actual chimney is so strong it will pretty much always overtake any tendency for the intake to back up (I hope that makes sense).

If we must feed it that much, then I do not even understand how it can burn less wood than a normal stove!

The problem is the too small feeding mouth, because it must be the smallest part.
So, is the real problem that it is too expansive to use large pipes for the exhaust!?!

An idea came to me, as I also want to see the fire and was planning a glass door.
The important size is the section of the horizontal fire place.
Is it really impossible to have a larger feeding mouth, if the horizontal pipe has the right size?

I just imagine my fireplace behind the window, with the vertical wood coming out, and the horizontal "small" duct behind...
Does it make sense?

I am hoping to burn chipped shredded limbs instead of trying to feed various sizes of random wood. I like seeing ideas though of how to bulk feed these things for extended burn though. Lots of creative people putting their minds together.

This is the solution that has worked jam free for me for over a month and a half:



I need to find a more natural binding method. Any suggestions on what I might be able to grow in Missouri that would be suitable for binding these together?

I've also done an experiment today in burning green wood. Since I plan on using a poplar coppice, most of my wood will be quite small. Small seasoned wood causes boil overs in my furnace. The moisture in the green wood keeps the reaction slower to prevent that. Here's some more info on this experiment which has worked far better than I ever expected. At the moment, I'm over 12 hours into the experiment with no smoke production.

Xisca Nicolas wrote:

Sandra Ellane wrote:I'm with you Dale, I'm trying to figure out a way to not have to sit full time near the stove and feed it. Even Mr. Evans admitted in his book that this is a drawback to a RMH.

Maybe part of focus needs to be on the exhaust rather than the input, to ensure that the actual chimney is so strong it will pretty much always overtake any tendency for the intake to back up (I hope that makes sense).

If we must feed it that much, then I do not even understand how it can burn less wood than a normal stove!

The problem is the too small feeding mouth, because it must be the smallest part.
So, is the real problem that it is too expansive to use large pipes for the exhaust!?!

An idea came to me, as I also want to see the fire and was planning a glass door.
The important size is the section of the horizontal fire place.
Is it really impossible to have a larger feeding mouth, if the horizontal pipe has the right size?

I just imagine my fireplace behind the window, with the vertical wood coming out, and the horizontal "small" duct behind...
Does it make sense?

For me the slide is just one part of an array of choices that I see would be useful for the constant stoking that might be required in heating greenhouses, wood kilns, wood fired pottery kilns and heated swimming pools. Your average guy who is heating with a RMH will likely never need an autofeed. So in that way, I'm solving a problem that doesn't yet exist. If I manage to get city hall on board with my grand vision to create a campground with all of the aforementioned devices, auto feeding will be desireable. To see just how much wood I plan to burn, check out --- DALE'S FIRESTORM OF HOT IDEAS – Includes forge, foundry, pottery and glass kilns and a heated pool. https://permies.com/t/19908/stoves/DALE-FIRESTORM-HOT-IDEAS-Includes

Dale Hodgins : I think you and Geo Shoonmaker are both on the cutting edge of the simple breakthru - an auto wood fuel feeding system - that will make the
Rocket Stove Mass Heater more user friendly for the average person considering D.I.Y. home heating choices ! Keep up the good work ! Be safe, Keep warm,
PYRO Magic - ally yours, Allen L.

I also like the thoughts of not having to tend the stove so often and have had the following thoughts scrambling around my little peabrain: What if a sealed metal locker was used to load the wood over the burn hole. Completely air tight so the fire could not go up inside, but the draft was taken from the bottom and drawn across the lowest part of the wood. Like dropping the wood into an inverted T-pipe. If the draft needed to be raised because of smoke backing up, then an elbow and maybe a little extra pipe to get the height you need. With the air passing along the bottom of the longer logs and the rest of the logs inside the sealed locker then fire shouldn't be able to climb the logs. Plus you dont need a high ceiling to load because you open the door, load the wood, shut the door. Whaddayathink? Im here to learn so give me your best feedback!

Linwood Bridges wrote:I also like the thoughts of not having to tend the stove so often and have had the following thoughts scrambling around my little peabrain: What if a sealed metal locker was used to load the wood over the burn hole. Completely air tight so the fire could not go up inside, but the draft was taken from the bottom and drawn across the lowest part of the wood. Like dropping the wood into an inverted T-pipe. If the draft needed to be raised because of smoke backing up, then an elbow and maybe a little extra pipe to get the height you need. With the air passing along the bottom of the longer logs and the rest of the logs inside the sealed locker then fire shouldn't be able to climb the logs. Plus you dont need a high ceiling to load because you open the door, load the wood, shut the door. Whaddayathink? Im here to learn so give me your best feedback!

I originally set my rocket stove up just like you described. It worked very well except for one thing - the coals got so hot from the intake air rushing over them that the wood in the feed tube would gasify. Then when the lid was opened, smoke would billow out, making it unpleasant to feed the fire. If you took too long adding wood, the smoke would ignite, leading to a feed tube fire. This would happen with or without forced air induction. BTU output and thus wood consumption went way up. It works in a rocket stove only if the feed tube is really short and you wait to refill until the wood is nearly consumed before refilling. If the feed tube is long, dangerous amounts of pressure build up from the woodgas, and leaks will manifest themselves as smoke billows out. Whether or not the system will work for you is based on how long you need to burn to heat your home. In a RMH, you can probably get away with a shorter tube. Since I'm using water as my heating medium, the fire has to go continuously, making the long feed tube a necessity.

I think there is a great potential in a system like this if you wanted to produce woodgas to run a generator. It is something that would be well worth developing if you wanted to produce heat and electricity at the same time.

Luckily for me, it was easy to switch the air feed to the top. A PC fan powered by a deep cycle battery charged by a 15 W solar panel provides just enough push to prevent the draft from going up the feed tube, which is actually longer than my chimney.

Did you shut off the air intake (down below the locker) before opening the feed tube(door) to allow the draft to be taken from inside the locker with the door cracked slightly? I thought this might pull any smoke inside through the system to be burned. That's only a thought though, obviously you have real world experience in this area. I also thought of using water as a heating medium to run through my garage floor since I have the tubing already in. I have not built a stove yet because i am in hopes to have most of the details figured out before hand. (hopefully!) Thanks, and Merry Christmas to all!

Linwood Bridges wrote:Did you shut off the air intake (down below the locker) before opening the feed tube(door) to allow the draft to be taken from inside the locker with the door cracked slightly? I thought this might pull any smoke inside through the system to be burned. That's only a thought though, obviously you have real world experience in this area. I also thought of using water as a heating medium to run through my garage floor since I have the tubing already in. I have not built a stove yet because i am in hopes to have most of the details figured out before hand. (hopefully!) Thanks, and Merry Christmas to all!

I've tried that, but the problem lies in the volume of smoke being created by the wood gasifying in the feed tube. It creates a dangerous situation familiar to those who use wood gasifiers. When you shut the intake from the bottom, the fire smothers, creating more smoke. When the feed lid is opened, smoke billows out and fresh air rushes in, creating potential for explosion. I had a small one, luckily for me, it only blew the cap off and startled the living crap out of me.

It sounds like water would be a great heating medium since you have existing tubing. This will require a pump, so since electricity will be incorporated into the system, it is no problem to use a wall wart to power a PC fan to force just enough air flow to prevent backfire. I've been using the fan to assist intake for 2 months now with no problems. A peltier module might be able to power it off waste heat from the stove too.

Thanks for letting me benefit from your learning curve! Definitely some issues to deal with by trying to modify these stoves for those of us who cant spend all day using less wood. You saved me a lot of time, headache and money so I think I'll keep researching this site more before I decide which way I will build mine. Maybe this summer...... Thanks, I will keep checking on your progress also.

Dale Hodgins wrote:Regarding the post directly above – I'd like to see a video of how this thing works. I'm not sure if long poles of twisty firewood would fit into that contraption which holds dowels. Much of my long material will be curved and rough branch material. ---- I won't be trying anything complex. No moving parts equals nothing to break down. I'm going to go as close to vertical as I find practical. No plans to stack very much if anything on top of one another. I could see sending several pieces down side-by-side but I think stacking them would create problems. I have some sheet-metal at the property so I could easily do a quick outdoor mockup and try the slide on various angles and with various types of wood. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- regarding earlier posting------

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I've said that I plan to use a U-shaped slide. The font available doesn't show the actual shape. It will comprise no more than one quarter of a complete tube – 90° on the protractor. The higher the sides, the more likely it would contribute to airflow issues. I also plan to end the slide about 1 foot above the J tube. The last little chunk of each log will drop to the fire independently of the slide. A half barrel ring will prevent anything that bounces from escaping into the room.

My plan is to run only a couple of sticks at a time down the slide. If they were piled a dozen deep, then any flattish boards or other wood on top could effectively become a lid which would turn the slide into a chimney.
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The need for constant tending and inability to burn long chunks of wood are the only non-user-friendly issues I have with rocket mass heaters. I haven't heard of anyone burning large diameter material. For a large unit heating a big home or commercial space it would be nice to not have to split everything into toothpick sizes.

Does anyone know if a heater has been built to accommodate large dimension firewood?

I've already gathered some of the materials necessary for this contraption and the first one will be built in my greenhouse/flophouse. Only after a successful season in the greenhouse will I go to the trouble of building an attractive stainless steel version to feed the main heater inside the house.

Look forward to seeing pictures when you get around to prototyping.
Assume with all the discussion about chimney effect, you won't let it burn unsupervised until you've thoroughly worked out the kinks.

Regarding quarter-tube slide:
Yes, more likely to work out for you than a full tube. You'll be adjusting the angle like the fellow with the pellet hopper did, until you get the right compromise between feed rate / smokeback.

But metal is still conductive, as are the sticks. There will be no cooling downward air flow around the sticks in the feeder, just radiant and conductive heating. There is a 'fireback effect' even from shallow overhangs over the feed tube.
The only serious fires I've heard about in connection with rocket mass heaters involved over-long wood. (Granted, simultaneously one of these cases had a stack of kindling drying atop the barrel...) If you want a six food true vertical feed, J-tube basic setup, the proportion would be to make an 18 foot heat riser - you're basically combining a charcoal burner's kiln with a clean-burning factory smokestack at that point good luck finding refractory materials to handle that conflagration. (It would need to be a large enough system that the flame path went fairly far up the 18 feet of heat riser).
Systems over 8" diameter equivalent have been built, but tend to need higher-rated refractories as they can approach the theoretical with temps over 2400 F even in 8" systems. Up to maybe 3000-3300 in larger ones (10" to 12" diameter equivalent CSA). There's a little bit of thermal feedback as the tunnel and riser materials initially soak up the flame's heat, and then start contributing it back as they re-radiate.

Re: other post: Yes, the feed does have to be constrained to the same flow area as the horizontal tunnel. Air being forced down past the sticks is the only thing that forces the smoke / wood gas to flow down into the firebox instead of up. If the stick protrude above the feed lip, or if the feed is too large, or even if you get one big flat chunk acting like a damper up by the burn tunnel end and a gap behind it, there's an increased risk of smoke wicking back up the sticks without enough air drafting downward to suck it back down.
It's a siphon; doesn't work real well if it's loose or leaky.
We ran some math on the air temperature involved and we now tend to run ours with the air feed reduced with a couple of bricks to about 25% to 50% of the burn tunnel CSA. Anything more, and you need a full feed tube so that the packed chunks of wood themselves serve as the air supply damper. (You get about the right air supply with good packing of round pole wood, by the by - the air space ends up being maybe 1/3 of the total volume.)

I can burn whatever size wood I can fit in my feed - have burned a single dry 5" diameter log on its own coals in my 6" heater, left it unattended and woke up to find a single 1.5" sliver of charcoal.
My 8" takes up to about a 7" round - that seems like the size of pole you're talking about. I have to get the coals going first, and the wood has to be definitely dry.

I think the reputation for needing smaller wood is mostly based on the rocket cookstoves - they almost all have horizontal feeds, and the cook must continually tuck the burning wood further in to maintain the fire in the correct place. This is something that the women who used to cook on a three-brick 'stove' are quite accustomed to and don't find an inconvenience; but it would be one for someone converting from a big-bellied woodstove or thermostat-controlled oil furnace.

The J-tube feed is designed to reduce the work of feeding the stove, while allowing continuous burning as opposed to other masonry heaters' batch burns.
If you are shoving kindling down a rocket mass heater all day, it will sometimes choke on the coals after a while; bigger wood works better.
Big dry wood can burn with only corner-of-the-eye attention for an hour or two at a time.

On the whole I think the idea of burning longer poles is the wrong kind of lazy for me.
End grain dries faster; so poles won't dry as quickly, especially if one butt is resting on the (damp) ground; therefore you'll be burning damp wood, so you'll need twice as much of it. Plus it tends to smoke back more because it's conductive enough to start boiling the sap out higher up the sticks.
The feed sounds like a bigger obstacle in the room, the long poles a bigger nuisance to get through the door. If you're trying to set up the stove outside the house, and then make it self-feeding, with a feed system that may make it too dangerous to bring back into the house... you're definitely going to be wasting a lot of the heat, and efficiency the stove's supposed to offer.

I keep my stove near at hand where I can tend it, and burn the right size wood so I don't need to get up from my chair any more often than I would anyway (the stove's along my path to either a cup of tea or a toilet break). I literally hand-sawed more than half the wood we burned last winter, to bring it down to a size that fit our feed tube - the difference in smokeback rates was that significant with even 6" sticking up. (We extended our feed tube this winter to its full permissible height, which just so happens to fit the firewood perfectly as sawn, leaving me feeling a bit silly and searching for other forms of winter exercise.)

But I've heard enough people who share your view of the matter, and the relative convenience of less sawing. You have plenty of interested eyes watching for your greenhouse experiment. Might as well give it a try.

We talked with one guy who came up with a different system with a 4 foot feed box that was designed as a one-chance self-feeder; it was also in a greenhouse. The fellow was working two jobs and if the fire couldn't run itself, he wasn't going to stay up all night and re-start it. So no flashback problems for him, because it would be cold before he handled it again anyway. He did an insulated box full of pole / trim wood, got the fire started the usual way with downdraft air, then popped the box in place and opened a second air feed below. It was typically full of explosive smoke while running; if it did occasionally 'chug' with a backflash, he wasn't around to notice, and I think he had it pretty securely propped in place with nothing flammable nearby.

Like I said, not something I want or would even consider bringing into my home, but worked OK for him in a special situation with neither lives nor livelihood at risk.

-Erica

I agree with Erica, that it really isn't a burden to feed a fire in a home situation. My brother burns about 75lb of wood a day in a ridiculous, wasteful behemoth. He seems to enjoy the process of keeping it lit 24/7 especially when restarting his wet wood. I'm working on him and he's agreed in principal to go with some sort of masonry stove after viewing a few of Ernie's videos. Like me, he has limitless free wood, so it's about all of the work and a desire for more even temperatures.

I also enjoy fiddling with things constantly but I hate waste. I could see parking myself on the bench while watching a movie, so feeding a fire is something to do while feeding my face in front of the tube. My desire for auto feed has mostly to do with large consumers of wood like pottery kilns, metal smelting, commercial sized charcoal retorts and large water heating units meant for for many people or for a heated pool. All of the feed areas could be outside.

When I first got into the demolition and wood disposal business, I constantly dreamed up profitable ways to utilize the energy from this resource that I'm paid to get rid of. The RMH is normally meant to save wood. In my case, I would like to seriously scale up the quantity of material consumed to accommodate many more fire related activities than most people would ever consider. All of this wood gets burned one way or another anyway, mostly in big slash piles. I simply want to make it's utilization profitable and efficient and in the process take a big chunk out of conventional energy needs of the energy intensive activities listed on this thread.DALE'S FIRESTORM OF HOT IDEAS – Includes forge, foundry, pottery and glass kilns and a heated pool. https://permies.com/t/19908/stoves/DALE-FIRESTORM-HOT-IDEAS-Includes I expect to go with several large rocket stoves that pour effluent gas directly into the various devices. Most units will not be RMH units since the energy does not need to be absorbed and slowly released. This means no barrel, no bench and often no building immediately attached.

A few days ago, I saw my first real, live RMH. Imagine my disappointment when I found out that the RMH had been decommissioned and replaced with a less efficient masonry stove. It's in a public building where the hot barrel was a concern. The main reason it was altered is that many visitors who knew nothing about it were allowed to fire it and they often jammed wood deep inside the J tube and under the barrel prior to lighting. I could see dealing with this by cobing over the barrel and by making unauthorized fires punishable by 40 -100 lashes. Instead it was replaced. The bench and exhaust pipe are all that remain. I'm told that it worked well when used properly. Ernie, this is the one I told you about. --- Moral of the story --- Even the best technology can be rendered useless if you're not willing to ensure that it is used correctly.