Rocket Stove Design

Hello folks.  I am new to this forum and find it very interesting.  Let me first introduce myself My name is Shawn and I live in upstate NY near lake ontario.  I have a fairly broad background having studied chemistry, physics, and electronics but currently work as a nurse on Fort Drum.  I own my home but am tired of the high gas cost to heat.  I do not have a lot of money at my disposal and our code enforcement guy is a pain (seems like everything is wrong to him,  I should note I came from West Virginia and Western Maryland in the mountains) 
I want to design a small heater using rocket stove or rocket mass heater (or some possible combination)  I am thinking about the round kerosene heaters that put out a fair amount of heat and thinkiing how a rocket type stove could possibly do the same thing.  I have made a small one outside that looks like a volcano,  I took clay, sand and cement and packed it around a coffee can stove,  then lined the inside of the coffee can with adobe made with wood chips, clay, sand and cement.  this turned out to perform pretty well.  I basically want a small metal stove perhaps less than one square foot with a three or four inch chimney pipe vented through the wall.  If done right I feel this could heat the living room quite sufficiently to help offset the costs.  I also thought that by surrounding this with a thermal mass(though not a large amount,  perhaps enough to just hold a bit of heat for the daytime) then it could burn hot for a short time,  less than an hour or two and then radiate the heat from the small mass.  I also have thought about just using the metal itself and putting radiating fins on the riser to radiate much of the heat before it leaves the house. 

My question is this,  has anyone here designed or built a small space heater type of stove of this type and if so how did they go about it.  I have several ideas I have been mulling over (one is to build a heater outside and surround it completely with thick rammed earth walls and allow it to get hot  and pump the hot air from the enclosure into the house. any suggestions, or criticisms would be helpful.  I have also thought about a system that would serve also as a grill outdoors and heat the water or air and force it inside ( this way I can just say it is a grill for cooking)

best regards,

Shawn

Shawn,

Good luck.....seems to me I've seen another thread about small rockets for small houses.  Have you looked??

Don in the Mountains of West Virginia

Hi Don,  I have been looking.  there is a post regarding a small one but so far seems to be a brick type and not very 'portable', so to speak.  I am looking to build a small unit that could, in theory, be moved.  Perhaps a three or four inch riser and chimney, with a wall thimble that could be closed up perhaps in the summer and the stove stored,  or perhaps for whatever reason moved to another room where there could be another wall thimble.  Another idea I had would be with a window that has a slide down top that a thimble could be made to fit in the top(or bottom) of the window, sort of like an air conditioner would fit in.  This way it would be a temporary type heater.  I have the tools and knowhow to build,  but why  reinvent the wheel if someone had already made something similar.  I think something with no larger a footprint than a kerosene space heater.  I am stuck with using a hot burning steel chamber that burns efficiently with no smoke,  or with having some amount of mass to radiate heat or both.  If mass is used it would have to be in such a way it could be moved if need be (possibly stackable brick or block around a steel combustion chamber).  A rocket stove provides heat by insulating everything but the top where the heat comes out for cooking.  a rocket mass heater heats by radiation from a thermal mass.  I think I need something perhaps somewhere in between.  I will keep looking through the posts but anyone who has any information please let me know.

best regards,

Shawn

Here is a design I am thinking of but have not had a chance to get materials together.  As it stands,  this would have a base about 8 by 12 inches,  the riser would be three inches and the outer barrel 6 or 8 inches.  the combustion chamber would be insulated but the rest likely would act merely as a radiant heater(though adding a water jacket might even be an option.  Any ideas or suggestions?
by the way the height of the riser would be about 3 feet, though longer might be an option as well.
best regards,

Shawn

Harold,

This one's not exactly small, but it is 'semi' portable !  Maybe you can glean some indeas.



Don

I have been working out a rocket stove design for my 160 sq ft tiny house. Please see post: https://permies.com/permaculture-forums/8903_0/alternative-energy/rocket-wood-stove ; While my rocket stove is a little bigger then what you were talking it may still interest you. So far the testing I have done the stove seems to put out a lot of heat, top center of stove is over 800 degrees , while the exhaust vent is under 200 degrees. Of course if the top of the barrel had metal fins with a fan or added mass of some sort more heat could be extracted from the rocket stove before the gases are exhausted outside. Being weight a major consideration for me any major mass beyond the weight of the stove is not being considered. Also not wanting to risk any smoke back, a exhaust vent temperature of 150 -200 degrees should and does so far keep the exhaust gases flowing smoothly up and out the exhaust vent. My design so far uses sheet metal fittings and pipe for the feed tube, combustion chamber and riser, burn though I believe will occur in a year or two. I am already planning a much longer lasting burn chamber and riser from wielded 4" steel pipe. I hope to have my rocket stove installed in my tiny house soon. Vent though the roof is complete and the walls will have the final coat of polyurethane this week. I will be using 26 gauge sheet metal mounted 1" from wall and floor for a heat shield. I hope this design will help you with home heating needs.

Umm.. Y'all??

You seem to be forgetting (or ignoring) the M in Rocket Mass Stove.. The MASS is rather important, without it you may as well use any other type of fire you care to mention.. In fact, MOST other fire devices will work better than an RMH minus the M..
Yes, a rocket stove WILL very efficiently turn wood into flame, but without the mass you'll be throwing it away too quickly.
Faster fire, faster heat, faster to cool again! You NEED the mass.

Donkey, may be there's another track. Doing a very tall heat riser and heat exchanger. Well, increase the  heat transfer surface or time. I already thought about two ways without using too much space. One is to use two stacked up 50 gal drums and a heat riser of the right size for this.  To increase this, i could make a helicoidal ramp in the heat exchanger between the wall of the drum and the heat riser. like the pic at the end of the air ramp text here. http://billpentz.com/woodworking/cyclone/BuildCyclone.cfm#AirRamp

This all along the lengh of the heat exchanger. Has obviously, to be calculated but this would make a may be more efficient heat exchanger. Due to longer travel.  I also thought about fins in the heat exchanger, to increase the exchange surface without restraining the flow too much.

HtH.

Max.

Thank you Satamax. I also believe in a rocket stove designs without needing the tons of mass. A stand alone rocket stove heating the room with scraps of wood safely is all some of us want. Besides isn't the room and all the objects in the room being heated mass? A well insulated home will retain heat for days, if not for many hours depending on building heat loss. Too much is being made on the added efficiency of the mass to the rocket stove design. The true area to extract the heat of the rocket stove is top center of the drum. Fooling around with the exhaust gases to heat a mass seems a little dangerous, I know it works, but it isn't the only way. For those folks with the cobb houses and a permies lifestyle, rocket stove heated cobb benches work great. But most of us depend on our furnace to heat the house when were away and need a alternative method to use when we are home to help offset the gas bill.

Hermit, there's several ways to skin a cat. It all depends on the time it takes to exchange heat, the surface of the heat exchanger. The medium to be heated, etc. IMHO, to warm up a room fast, instead of cob, i would use water (with thermosiphon and a radiator) to cool down the last exhaust fumes. Far more eficient, Tho, it doesn't retain heat.

Hermit DeLuxe wrote:
Thank you Satamax. I also believe in a rocket stove designs without needing the tons of mass. A stand alone rocket stove heating the room with scraps of wood safely is all some of us want. Besides isn't the room and all the objects in the room being heated mass? A well insulated home will retain heat for days, if not for many hours depending on building heat loss. Too much is being made on the added efficiency of the mass to the rocket stove design.

Indeed, well insulated homes can hold heat for some time.. Though over-tight houses can lead to air quality issues and a fairly constant exchange rate is necessary for best health of occupants. You're relying on air as a heat storage medium, which it's not that good at. Air is a better insulator, though it is useful for moving heat about.
I think you'll find that without the mass, rocket stoves (as space heaters) will perform a bit like pot-bellied stoves do. They should run high, providing a lot of heat, perhaps even a bit too much for a time, then cool off quickly after the fire dies. Also, it's worth noting that since the firebox (in classic rocket style) is so mall relative to other stoves, the actual heat output of the thing won't be nearly the same. Wood's got a finite number of BTUs in it and while rocket stoves WILL wring out more from each stick, they eat a smaller volume at a time AND they tend to be more fiddly about it 'ta boot.
Don't knock thermal mass short. The only kind of stove that I know of that can compare to an RMH (rocket mass heater) for heating efficiency and quality is Masonry Stoves, which ALSO weight a ton (literally), have a lot of thermal mass, require a skilled mason to build and cost $10,000 at the cheap end.. Heck, pot-bellied stoves can be improved (hugely) by adding a heavy stone surround..
The (most) important part of the thermal mass is it's slow, timed release. Most stoves produce more heat than is strictly needed (till the fire goes out).  A HUGE amount of that heat is radiated immediately into the walls of the space and  works its way directly outside without passing through YOU first.. Mass slows it all down considerably, leaking heat to the space slowly, giving YOU a better chance of intercepting it on it's way outside. The RMH bench-thing places your body in direct contact with the storage medium which cuts out the middle-man (so to speak) and is a great way to spend a rainy afternoon.

The true area to extract the heat of the rocket stove is top center of the drum. Fooling around with the exhaust gases to heat a mass seems a little dangerous, I know it works, but it isn't the only way. For those folks with the cobb houses and a permies lifestyle, rocket stove heated cobb benches work great. But most of us depend on our furnace to heat the house when were away and need a alternative method to use when we are home to help offset the gas bill.

Fooling with exhaust gasses to heat mass is EXACTLY what the very expensive and quite well time tested Masonry Heaters do. Also, I think it's important to realize that our houses don't really need heating, the people in them do. Seems to me that keeping that simple distinction in mind can take us a long way into the smarter, lighter, easier to accomplish type solutions that we can all use.

I understand the need for lighter weight heating methods though, so I get the point..

If I wanted to build a lightweight rocket heater, I'd build a metal bell stove. Instead of the barrel, I'd weld up a steel box with a MUCH larger volume, something like a 3' x 3' box, about a foot taller than and surrounding the heat riser. It would be VERY important to place the chimney at the bottom of the box.  Bell stoves are good at evenly distributing heat, also placing the exhaust (of the bell) at the bottom gives you the means to play fun with fractioning of the heat (the coolest stuff will find it's way out). Multiple chambers can be made, each running into the next that  isolate heat zones for different jobs and/or provide more surface area for better exchange, etc.
For simplicity, single bells would be hard to beat. The bell(s) could be made with brick as well for a reasonably medium-weight stove.

Thank you Donkey and Satamax  for your reply's. You both have real good points. My point is there has to be a way to extract most of the heat produced in a rocket stove at the heat focal point and not with the exhaust vent gases. The best mediums I see to extract the heat from the focal point would be mass, water and air. Mass as Donkey described a bell stove with chambers or the rocket stove drum top and sides covered with bricks or cobb. Water as boiler or water heater type heat extraction, dangerous without the proper knowledge, materials and controls or electrical production using a water cooled thermoelectric generators. Air as fins wielded to top of drum with a wood stove fan or open ended tubes wielded to side of drum with convection to move the air. I will be personally trying the fins or tubes to extract the heat more efficiently.
Also I have found the minimal mass of my rocket stove seems to keep putting out a lot of heat for twenty or thirty minutes after the flames has gone out with just a bed of glowing coals. A efficient a low mass or no mass rocket stove is possible and I hope to work out a working design or at least something that works for me. I hope for more banter on this subject, Thank you.

Hermit DeLuxe wrote:

Also I have found the minimal mass of my rocket stove seems to keep putting out a lot of heat for twenty or thirty minutes after the flames has gone out with just a bed of glowing coals. A efficient a low mass or no mass rocket stove is possible and I hope to work out a working design or at least something that works for me. I hope for more banter on this subject, Thank you.

20 or 30 minutes? A  proper mass heater will be warm for 12 to 24 hours after a two or three hour burn. The same wood is burned, but in a massless stove one gets 2.5 to 3.5 hours of heat, the mass heater gives 12 to 24 hours of heat from the same wood. The surface of a mass heater should not get too hot to touch. The air heater burns on contact... not just skin, but also the air we breath... speaking of the air we breath, an air heating stove gets hot, mostly the room gets too hot if it is burning cleanly, so the operator tends to "slow" the fire down by decreasing air in. Then the rest of us get to breath half burnt fuel and get sick, the flue build creosote and the house burns down when it ignites. The mass heater burns as fast as it can producing mostly CO2 and water... the mass collects the heat and releases it slowly over many hours.

A non-mass heater is like doing rain water collection with a cup, as long as it is raining a drink of water can be had. A mass heater is like doing rainwater collection with a barrel.... The water may last from one rainstorm to the next.

The down side of a good mass heater is that it does not feel warm right away... it seems it is burning like crazy but nothing is happening till the heat makes its way through the mass.... then it feels nice.... for a long time after the fire has gone out.

Sorry Len, i gonna be picky.

You say "

The mass heater burns as fast as it can producing mostly CO2 and water...

"

But mass has nothing to do with this full burning. It's the oxygen intake of the stove which makes the burning cleaner.

And, if the whole of the heat is  already extracted before it reaches the mass, the mass serve no purpose. I know it's not. That's why i'm trying to work on this side. Extending the size of the heat exchange surface.

Satamax wrote:
Sorry Len, i gonna be picky.

You say ""

But mass has nothing to do with this full burning. It's the oxygen intake of the stove which makes the burning cleaner.

And, if the whole of the heat is  already extracted before it reaches the mass, the mass serve no purpose. I know it's not. That's why i'm trying to work on this side. Extending the size of the heat exchange surface.

No the mass doesn't... the operator does. Unless the area to be heated sucks a lot of heat, the operator is going to run a mass free stove at minimum ... that is smouldering. I get the effects of that from my neighbour who runs two of them in his tiny house and most of the fuel goes out the flue and it stinks when the wind blows this way. His stoves could burn clean and fast... but the inside temp would be too high for human life (certainly for comfort) and the heat would make its way through the walls and out of the building faster because of the higher temperature difference (R value may slow this... making it even more uncomfortable, but R value is just a measure of speed of heat travel. Even at high R value, heat still moves and moves faster the higher the temperature difference). The idea of mass is to catch the excess heat, the heat that is too much for the occupants when the fire burns clean, and saves it for later, much later. Then because it releases it slowly at a lower temperature, less of it migrates through the insulated walls.

Only in North America, where most people have come from Britain and a mild climate, are low mass stoves used much. Look at northern Europe, Finland, Russia, Poland etc. Even the poor peasant uses a high mass heater. They can't afford not to.

I know... you are not from North America, but you are in a milder climate where tradition has not had the force of necessity of incorporating high mass in heating appliances. The use of high mass heaters in North Europe was the result of a fuel shortage. Kind of like we have now. Cheap Gas and (at least for many North Americans) free wood, have kept fuel wasting tech in the main stream... big business would like to keep it there so they can sell more gas/hydro.

Hi Len.

Mild climate? Here's my winter office, in the end of april

Satamax wrote:
Hi Len.

Mild climate? Here's my winter office, in the end of april

Ya, most of North America is like that too. The thing is not about what is, but where people's traditions come from... or maybe more these days, what business wants to sell. I thought you were in France, for some reason, where a lot of the coastal cities are quite mild... compared to Siberia anyway. In your case with a lot of stone walls, a hot stove that heats those walls may work not too bad. In a well insulated, stick house where the house itself has no mass... well the one person who has written about their experience with a rocket "no-mass" heater says it warms up the room really quick on little wood, but then they put the fire out as it is getting too hot and the room cools fast too. This with a person who's heat riser is only 3inch dia. With a big enough space and enough heat sink in the walls, a 6 or 8 inch system with no mass may be putting out just enough heat running full bore. That would be a "special" case.

Hey Lem.

That's france, and southern too

But i'm in the southern alps, right next to the italian border. My flat and workshop are around 4900 feet high.

I'll see if i can extract enough heat to make the workshop uncomfortable I'm planing an air jacket around the radiator, with tubes and a fan to get the heat to the insulated part of the workshop.

My concern was not so much designing a rocket mass stove but more of a small space heater using rocket stove design with a small footprint and a small chimney that burns efficiently and hot for a short time.  While the rocket mass design is understandable and a very good one, I do not at present wish to put that much weight in my house as it would take a good bit of shoring up(even though my house is made entirely of hardwood)  I want something simply to warm it up in the living area for a short time occasionally.  While surrounding with brick for some mass is a possibility,  I still want as small a footprint as possible.  kerosene heaters put out a good bit of heat for a small footprint and I think the same effect can be obtained from a small footprint rocket stove where it would burn hot for a short while to warm up the area then be out.  I am still mulling over my options but because money is tight I do not want a massive chimney which would cost money and attract attention.  if burning efficiently I should be able to have a simple vent outside perhaps 3 or 4 inch diameter.

Satamax wrote:
Hey Lem.

That's france, and southern too

But i'm in the southern alps, right next to the italian border. My flat and workshop are around 4900 feet high.

I'll see if i can extract enough heat to make the workshop uncomfortable I'm planing an air jacket around the radiator, with tubes and a fan to get the heat to the insulated part of the workshop.

Go for it! we are all experimenting anyway... I've had to make adjustments to mine already... and it isn't even finished.

toolman911965 wrote:
I still want as small a footprint as possible.  kerosene heaters put out a good bit of heat for a small footprint and I think the same effect can be obtained from a small footprint rocket stove where it would burn hot for a short while to warm up the area then be out.  I am still mulling over my options but because money is tight I do not want a massive chimney which would cost money and attract attention.  if burning efficiently I should be able to have a simple vent outside perhaps 3 or 4 inch diameter.

Here is one similar to mine, 18 inch diam. but with 4inch riser and no mass:

http://streetjesus.blogspot.com/2010/12/rocket-mass-heater-project.html

Mine will have mass but still only be 25 inches in diam. unless I add more. I figure the mass will be about 700lbs. The water in a 50gal water tank might be 500lbs so not much more... (I know a cubic foot of water is just over 60lbs, but not how many gal/cuft... not sure how close to 10lbs/gal it is).

However, if I wanted to minimize weight, I would put a shelf part way up the tank and put the mass around the top for best effect. This could bring the overall weight down to 350lbs... less than a water tank... which a wood floor should be able to handle.

Len wrote:
Go for it! we are all experimenting anyway... I've had to make adjustments to mine already... and it isn't even finished.

I've made modifications too, as per the cyclonic part. The radiator out of a gaz botle. Btw, i've burned it yesterday, hoping that i'll get less fumes. But it seems that there's a kind of galvanizing underneath the paint. Mind you, it seems to have offgased alrerady, as when heating with a propane torch, it doesn't do anything. No yellowing or anything. I'm waiting for the refractory joints to dry up untill tuesday. I'll have to modify the chimney in the mean time.

Bye.

Max.

Len wrote:


Mine will have mass but still only be 25 inches in diam. unless I add more. I figure the mass will be about 700lbs. The water in a 50gal water tank might be 500lbs so not much more... (I know a cubic foot of water is just over 60lbs, but not how many gal/cuft... not sure how close to 10lbs/gal it is).

Len, just thought since I lurk around here.
7.48 galons to cubic foot.
8.34 pounds per galon.
62.4 pounds cubic foot.
These are figures for water at a specific gravity of 1, and realize this would be much like at the temp that would be drank out of the tap.

ytram wrote:
Len, just thought since I lurk around here.
7.48 galons to cubic foot.
8.34 pounds per galon.
62.4 pounds cubic foot.
These are figures for water at a specific gravity of 1, and realize this would be much like at the temp that would be drank out of the tap.

Which gallon? An imperial barrel is 45 gal and 55us gal.

Looking it up, the imperial gallon is based on 10 pounds of water.... how can you tell I'm from Canada? 

Len wrote:
Which gallon? An imperial barrel is 45 gal and 55us gal.

Looking it up, the imperial gallon is based on 10 pounds of water.... how can you tell I'm from Canada? 

Sorry! US galon.

Any chance you could make a heat capture system like the one used for JUCA stoves?

sorry added a web address  http://mb-soft.com/juca/index.html