Experimental RSMH... Feedback?

Hey folks!
I'm experimenting with a few variables for a RSMH, and I would appreciate some feedback por favor.

Sorry if these designs have been discussed already, or maybe they are layed out in a book somewhere. Ok on with the designs.

So first the air inlet is as low as possible to increase the pressure differentiation between it and the top of the riser (which i two barrels tall)
The air inlet is also one of those spinning thingies on top of garages and sheds- I figure it will cause turbidity early in the burn chamber.

Then the exhaust is directed from the heat riser, down the double barrel, and back around the burn chamber for greater insulation once its fired up. Not sure it will make a lick of difference seeing as how high the R value is of the fire brick that is used constructing the burn chamber.

Next is having the wood inlet enclosed by a 30" barrel where exhaust preheats the wood. This seems like an obvious mod that should be done on every RSMH. Again I am sorry for reiterating anything that may have been already discussed/or is common knowledge.
Preheating your fuel (wood in this case) and ridding it of as much moisture as possible will result in higher combustion efficiency right?... That combined with cool dense air should improve it somewhat? IDK, tell me what you think!

I guess preheating the wood also acts like a humidifier, SWEET:)

There are also multiple exhaust outlets for zone control, and 3" ports throughout for shop vac clean out.

Thank you in advance for taking the time to read and hopefully respond!

-I will follow your build with interest, there are traditional uses for RSMH, and this isn't one of them, which is good we need to' break new ground' to grow. I will be surprised if your 'spinning things' has any affect on air flow or turbulence, what it will do is add audible and visual clues to how well your RSMH is working.

The RSMH modified to incorporate a J-Bend, as promoted by Ernie Wisner and others, is there in part to stop the thermal-syphoning of heat out through the Rocket Stove and the Thermal Mass robbing you of the heat you have stored in your RSMH .
Unless the Spinning thing is removable you don't even have the option of blocking your air flow at your feed tube, so I expect it will be spinning all of the time that there is any heat in your thermal Mass, if your RSMH has a J-Bend it should stop spinning when your fire goes out !

It would be interesting to run two units, one gently drying your wood and one where the RSMH air feed was directed past the wood, pulling off moisture on its way to the feed tube, With your Rocket working properly and your thermal mass doing its job you can probably recover the latent heat of evaporation to add to your units efficiency.

With your 2 barrel high Heat Riser you may be able to get away with slightly cooler air temps. at start in your initial combustion zone as its the re-burn that maximizes your efficiency, traditionally RSMH's use warm air out of the room to help produce the high temps for a good clean burn, knowing that the heat from room air will be re-introduced to the thermal mass.

Again traditionally the RSMH is considered to be a 'Space Heater' not a whole house furnace, screw tradition and try it your way. I do think using multiple exhausts for zone control is problematic, it traditionally requires Individual Thermostats and booster fans to push your air to the zone where its needed.

Stationary air at 90 degrees feels warm, air going past your thermal mass and heated to 90 degrees needs a slow speed air flow not to feel coolish. As your thermal mass cools down it still contains lots of heat but it cant push it out to its skin to be radiated out to the air fast enough and you will need an air temp. thermistor to regulate air speed as flow rate.

If i wanted to use my thermal mass as a pre heater to help me heat the whole house I would duct my "multiple exhausts'' to the cold air return on a conventional furnace, replace the blower fan to one rated for use in high temps and use multiple manual air ducting dampers for zone control.
'
Again you are 'breaking new ground' and we will certainly learn something new from your creations please keep us informed as to your results and remember - 'your milage may vary' Pyromaticly your Allen L.

- looking at your sketch again,did you mean to split your exhaust gases into three stove pipes and take your exhaust gases in three directions ? Please note that the longest run with the fewest elbows/'Tees' will take the largest amount of exhaust gas flow, (and wood ashes) just like the tallest vertical chimney will have the most 'DRAW' !
As a safety issue three stove pipes= three times the problems, here safety and tradition rule! This is a bad idea, I had to look several times to believe what I was seeing !

In order to call Your Rocket Stove a Mass Heater it has to have a mass to heat, otherwise all of your heat not radiated by your barrels goes out through the stove pipe as hot exhaust gases !

I am red faced that I did not catch this earlier, so I am going to blame it on being tired and dirty spectacles.

Even though your 1st sketch has problems do not be discouraged, I would however go to www.rocketstoves.com and order a downloadable copy of Ianto Evans' great book 'Rocket Mass Heaters' $15.00u.s., and read it carefully as carefully as I should have read your post. With your active imagination and a little background you will be building good Rocket Stove Mass Heaters in No time at all and i will wash my glasses ! Allen L.

Thank you for the VERY detailed reply! WOW!

After seeing your reply Im not sure wow well I conveyed my design conceptions. Actually after rereading what I wrote I know I could have done a much better job, sorry:(

1st) Yes, there are 3 different exhaust ports which can all be closed and opened independently from one another. I was planning on having one go through a very large cob bench, another under the kitchen floor, and the last running though cob stairs ( lots of surface area that I dont want to waste).

2nd) From what I understand about combustion, specifically wood combustion, turbulence in the burn chamber should result in a cleaner burn.... Not sure though since I've never built one much less ever seen one! lol

3rd) The feed tube which supplies wood to the burn chamber is surrounded by a 30" barrel, heated by exhaust gasses coming from the riser/double barrel. Kind of a combo 'preheat/dry out your fuel' and 'humidify the air' thing. After all, why burn cold or even room temp logs when a small design altercation can increase efficiency? The reason I want it to give off hot humid air is because it gets so bloody dry in the winter here in Norther New Mexico.

4th) Well I guess thats actually all there is. Do you really think zoned exhaust is a bad idea? Has it been done before?

- if you take two chimneys or two funnels, the taller one draws/drafts better every time, adding Elbows and 'Tee's changes it but certainly does not make it better, please abandon this idea two or even three entire Rocket S.M.Heaters will give you less trouble than you are buying for yourself !

The romans built villas with raised floors with passages to carry hot exhaust gases to warm their floors - all over their occupied territories to include England up to Hadrian's Wall
The heated floors were called hypocausts which loosely translates as below heat or below fire! I leave it to you to make a report if they used more than one channel !

There is a companion forum on cob with multiple threads to follow and gain knowledge, outside of that you are in the land of adobe which is related to cob and any thing you learn creating one can be carried over to the other !
The biggest difference i have observed is in the amounts of water used in their individual constructions,

I will let you in on a little builders secret, air is a much better insulator than it is a carrier of heat, the more moisture you put in the air the warmer you should feel, up to a point, and that would be about where high moisture starts to turn Cob Soft and spongy !

I really really hope the next time we get together you are thanking me for turning you on to Ianto Evans book! Pyro AL

"if you take two chimneys or two funnels, the taller one draws/drafts better every time"

This would be true if I had multiple heat risers. Draft comes from the pressure differentiation of the air inlet and top of the heat riser(this is why your exhaust outlet can actually be lower than your air inlet). Having multiple exhaust ports AFTER combustion is not the same as having multiple chimneys. I realize that I can only have one 'zone' open at a time, other wise the exhaust will follow the path of least resistance. We are not thinking of the same thing. When different zones are being used the impedance of the exhaust will be determined by the length/amount of J's & T's within that one zone; and each zone will be different.

Also, than you for the builders tip on insulation and cob. Last May/June we had single digit humidity!

- IF you are going to have THREE (3) dampers, at some point a "thing" will happen and all of them will be closed at once , Pre-pay your life insurance, make a will, and live alone !

I do not like this idea, it is a very complicated way to commit suicide. I wish i knew what I could say that will move you from this path ! Please get a second and a third opinion on this !

I do not want to say i knew you before you took this direction ! Very Sincerely Allen Lumley !

Hi Mr. Gurry
hmm three dampers? why would you put three dampers on a stove of this kind? Have you built one to actual plan yet?

air intakes? low in the firebox no less.
and an ash cleanout in the side of the burn tunnel and feed tube.

how about you build one to spec and use it for a while then make a change use it some more and make another change. far safer then trying to do it all at one go. you might want to read many of these threads here where it has been outlined these very advancements you suggest. I believe you can search them.

remember if its not been tested outside by you it should not be brought inside by anyone.

Hi Richard! Regarding the 30" barrel heated by flue gases to preheat and dehumidify the fuel. The issue with this type of arrangement will be that you have a seperate air intake from your fuel intake, and therefore nothing to stop your fuel intake from becoming an inadvertent combustion chamber in a hurry. The same principle that makes your designed combustion chamber work so well will be at work in your fuel hopper (ie. draw). This arrangement can work if you have an airtight lid on your hopper, but then you don't get the desired benefit of removing the humidity first, and you have a serious risk of burns and/or smoke and volatile organic compounds entering your living space any time you open the lid to check how much fuel you have left or want to add fuel.

However, since you live in New Mexico, I think it would be easy for you to dry your kindling prior to use. If not, a passive solar kiln would be super effective and another fun project eh?

Hope this helps! Keep on thinkin'!

- Colin

Hi Richard,

I concur with a lot that has been said about your intended design.

While you are correct, that pre-heating the fuel will result in a better burn, your proposed system (were it to actually create enough draft to function as you intend) would easily heat the fuel too much. Even if you could control the heat of your intake wood cooker, you would still want it hot enough to presumably dry out the wood before it reaches the bottom and begins to burn. Rapid dehydration of wood, even 'dry' wood, is going to vaporize out a lot of the volatile oils that are a large part of the 'fuel' available in the wood itself. You would essentially be creating 'clear smoke' and pumping it into your house... and by 'pumping', I mean that by heating the intake, you would be placing a new draft engine on the front of your system that wants to pull air the wrong way. For the intended efficiency gain of pre-heating and drying out your wood, you would be creating a new efficiency loss by drastically reducing the efficacy of your fuel and making your draft work against itself.

You would be throwing a stone on both sides of the scale... and quite possibly tipping it the wrong way.

Plus, imagine the potential wood oil build-up (think of it as 'high-grade creosote') on the top lip of the heat jacket-- you could suddenly have a dangerous 'after-burner' effect with a ring of flames reversing your entire system. Scary.

Thank you all for the great points and tips about my post!
However I am too stubborn to throw this idea away. There is not a single problem that has been addressed which cannot be engineered out. Safety is rarely more than a few modifications away.

1.) Having the fire draft up the feed tube is certainly a problem, yet easily fixed. Simply put a lid with a small hole on top of the feed tube? Wouldn't this create a space of positive pressure due to the expanding gasses and humidity from the wood? A small hole would still let out humidity at a fixed rate (assuming a wood filled feed tube isn't enough). Secondly, I highly doubt this would be much of an issue beyond initially starting up the fire. Notice the heat riser is twice the height of the feed tube; Once a fire is started the path of least resistance is the heat riser in terms of BOTH flow rate and pressure difference.

2.) Regulating temperature of wood in feed tube. Gasification requires temperatures well into the high 300's Fahrenheit. What we need is a heat sink that acts as a thermal buffer to the fuel source. WATER? I say YES! Wrapping the feed tube with copper coils filled with water will regulate the temp well below gasification and double as a water heater. The bottom of the coil would be connected to a water tank, the top feeding into the same tank or a new one depending on your needs. No pump is needed obviously because of the thermo-siphoning effect.

3.) Having multiple exhaust ports.... Not one of you thinks this is viable? seriously?... From the stoves perspective having one zone open compared to another really makes no difference. And 'accidentally' opening more than one zone at a time will result in dangerous circumstances? I feel like I'm taking crazy pills. This is so EASILY be engineered out that it should be considered a 'non-issue'.

SORRY if this post offended y'all. I don't mean to be harsh, but come on..... lets be solution minded instead of obstacle minded. please?

The damper issue is that if all 3 could be closed you could have the exhaust backing into the house. It's not negative to point out serious issues is it?

Your right, it's not a negative. But it's also an easy fix.

Has no one attempted multiple exhaust ports yet?

Yes here is a stove with multiple exhausts:
http://www.flickr.com/photos/fishermansdaughter/5075543716/in/set-72157625122351115/

a beautiful project, but i believe no individual dampers, its posted on permies somewhere too,

jasper thanks for finding this, the related forum thread is '' ROCKET FLOOR MASS HEATER - - FINALLY COMPLETED AND IT WORKS! '' , in this case it was designed to run parallel exhausts without dampers, and slow the flow of gases to promote heat exchange. This is exactly what i was talking about when i said that everything else being equal the tallest chimney should have the best draw, however that would be a function of Gravity 1st and the heat pump/hot air engine created by the differences in the Heat Riser , and the Bottom of the Barrel 2nd .

While there might be a case for the use of part dampers to equalize the flows between pipes, I restate my Strong objections to Multiple dampers that could all be closed by a combination of misadventure and failure!

Most types of dampers lock on to their spindles by twisting in one direction and loosen for disassembly by holding the damper body and turning it in the opposite direction ! (or having it jam due to failure or misadventure )

Murphey's law and Entropy always wins, always ! !! Pyro-maticly - - Allen L.

Thank you for the reply and posting the link to another who was tried it:)

when i said that everything else being equal the tallest chimney should have the best draw

I am not sure our terminology is the same. I understand that you are 100% right on the above quote, however the 'draw' comes from the heat riser, and I only have one. Do you mean the exhaust port with least resistance will support the most gas flow? The exhaust tubes (from what I understand) do not create 'draw'.

however that would be a function of Gravity 1st

Also, I am unaware of the role of gravity in a RMSH. Was this not covered in Ianoto Evans book?

Thank you.

p.s- I will draw up a diagram of what I have been thinking about to control 'exhaust zone selection' in my next post.

Richard Gurry : In 1 of my 1st posts to this thread I did mention your Heat Riser (Single) was 2 barrels high! This and my repeated comment '' with 2 chimneys or 2 funnels the tallest one will have the better draw*/draft'', I may have added to the confusion !
You are right in considering the heat exchanger as not only a chimney but the primary chimney, but it is 1 of 3 with the horizontal and vertical chimneys, my comment was true and correct for a vertical chimney and generally correct for a horizontal chimney !
There is a Hot Air Engine created by the difference in the Temperatures between the Heat Riser and the barrels bottom, using that work energy to drive the exhaust gases through the Thermal Mass !
Your exhaust outlet can be lower due to exhaust gases cooling, condensing, and becoming heavier - GRAVITY
As previously stated your exhaust gases flow through the thermal mass as a function of temperatures created in the barrel! Within the vertical chimney reduced mass i.e. hot gases rise against GRAVITY !
'' Having multiple exhaust ports AFTER combustion is not the same as multiple chimneys '' How so, they still contain Hot Exhaust gases !
It will be interesting to see your FAIL Proof ''exhaust zone selection '' control, remembering that you will have to design a damper that can't be accidently turned backwards against resistance as standard dampers will FAIL if used this way ! sincerely Allen Lumley

DRAW is a non-specific term that implies the 'lift' created by an area of reduced Pressure not reduced resistance, as when wind moving past a 'draft' corrector, creates lower pressure !
This is also demonstrated by the ' lift ' created within a Straw when one 'draws' on the Straw !
Draft is a much more specific term with multiple meanings that I would not attempt to define without research !

Richard Gurry : check out the information to be found in the permies forum thread ''ONDOL,KOREAN FLOOR HEATING, these people have been doing it right for thousands of years so I'm Sending you there without any proof reading ! Pyro-AL

Just came across this thread in the "similar threads" list, and as several of the original questions were never fully addressed, thought it ought to be taken care of for future new readers.

In approximate airflow order:

* The heated jacket around the wood feed will as mentioned create a dangerous situation of hot wood above the main fire zone, and this will compete with the horizontal draft created by the heat riser. The riser may win, or it may not, at any given time. BUT, if you have the main air inlet at the base of the feed tube, there is no impediment at all to the fire burning straight up the sticks in the little chimneys created between sticks (an effect well known to anyone who has actually used a J-tube RMH), and you will soon get a roaring fire coming up out of the top of your feed. Sealing the top of the feed creates the issue, also mentioned, of making a reservoir for hot, woodgas-laden air which will flash into fire if given oxygen by opening the lid to inspect or feed.
What has been found in practice is that cooling the wood to as near room temperature as possible until it reaches the intended combustion zone creates the best actual results. The air intake rushing down past the wood from the top of the feed tube is an important component in this.

* The spinning intake port at the base of the feed tube will not impart a significant amount of useful turbulence inside the combustion zone, and has dangerous effects as noted above. Useful turbulence comes from the right-angle bends in airflow path in the standard J-tube, and from more recent refinements such as the "P-channel" and "tripwire", both of which can be looked up in this forum or at http://donkey32.proboards.com .

* A standard J-tube RMH does not need any additional ashpit at the bottom of the feed tube. The amount of ash generated is so small that it can easily be reached and scooped out with a sardine can every day or so, and an empty ashpit would put the ends of sticks which should be burning down below the moving air zone where they risk being smothered and creating charcoal which gets thrown out with the ash, just like a conventional woodstove.

* There would probably not be a net benefit from directing airflow from the bottom of the barrel after combustion to surround the insulated burn tunnel. The combustion zone should be so well insulated that not much heat escapes through its walls/roof/floor, and the benefit of harvesting the bit that does may not balance the added construction complexity of this arrangement.

* Three or more alternate paths for the exhaust can be done safely, but not by independent dampers which could theoretically all be closed at the same time. It could be done with a plenum with a sliding damper which allows one path to be open at any time, or half of two adjacent paths, but cannot be positioned to close off all paths. Two paths can be effectively controlled by a single swinging damper which closes one or the other path. (Erica Wisner has demonstrated this in a thread on this forum:
https://permies.com/t/34378/wood-burning-stoves/Questions-underfloor-rocket-heater .)