Rocket stoves in Greenhouses , our own forum topic

Methods and locations for extracting heat from the RMH exhaust stream for the purpose of heating a mass of water.

Since I haven't found a thread already and there's a lot of discussion on this thread about heating water for fish tanks and as a thermal mass I decided to start a separate thread to specifically address this.
Extracting heat from the RMH exhaust stream to heat water
Hope to hear from some of you there.

Good thread.

I have one going in regards to fodder I plan on growing in the back of my future GH/s.

I've given the RH a lot of thought because I would also be having my fish tanks buried within the back 3/4 of the houses using pond liners about 30' long x 5' wide, and 4' deep. Behind that would be fodder territory. I'm still trying to decide if I should use multiple rocket heater systems or not. One for the basic GH and one for water temp on the fish pond. These GH's would be aquaponic. I'm starting to think another way of maintaining FT temp would be a better idea, and to just use the rocket for general GH heating. But I'm not against heat exchangers being used in conjunction with the RH thermal mass to maintain FT temp. Although, it would be nice to not require anything that needs batteries or electricity to run other than the FT pumps.

I have not gone threw the whole thread yet, but reading the posts, It occurred to me to ask if anyone has considered furnace cement? I'm a hobby metal caster, and this stuff is set up for build your own furnace guys/gals. It's a great insulator and hold a lot of heat energy, will not crack, or break apart of done right and allowed to cure properly.

Too many links to copy and paste them all. Here's one of my old metal casting blogs. Link list on right side of the page for supplies. http://bluecollarmotosmetalfoundry.blogspot.com/

Chris Duke : Nowadays I look at the prices for Refractory furnace cement and blink, It would cause my Scottish Ancestors to turn over in their graves, if I tried to use it as
freely today as in former days ! A quick look at your site and I understand That you are successful in using this to make value added Parts for bikes, so you are definitely
coming to this discussion with information to share and I hope this can grow into a new topic/Thread all by itself !

Basically, and I admit that this is 2nd/3rd hand information, We have two immediate problems, Regular furnace cement dries very hard and Has a very low expansion rate.
While These are conditions shared with "fire Brick", The two do not often play well together.

In constructing The Burn Tunnel We end up "Roofing Over'' the Top of the Burn Tunnel between the Feed Tube and the Heat Riser,by setting bricks on the top "Bridging" and
closing in the top!

Specifically, When Refractory Furnace Cement is used to attempt to lock the (usually) 9" bricks in their place on the top of the burn tunnel, The different expansion rates,
and the Final hardness of the cured Furnace Cement has led to some problems with fracturing and spalling of our fire brick, There has ben a reluctance to experiment with
Furnace Cement which gives us this problem and so we are stuck with the same traditional 'Fire Clay' and sand low expansion mortars which are more forgiving !

This is just merely restating the obvious, and Yes, sometimes I do hear a little voice saying 'But, but, But, we've always done it THIS Way' !, Thats why we have to welcome
new members with new ideas!

I would think that you would have problems with the different expansion rates, (and Vibration) on your parts, but it seems to be working for you! What's your secret! and
what do you use for shaping tools!

For the Crafts! Think like Fire, Flow like Gas, Don't be a Marshmallow! As always, Comments and Questions are solicited and Welcome ! PYRO - Logically Big AL !

I have been away from the forums for a while but have built a greenhouse 24x56 and i'm at present building a rmh when i figure out how to post pictures may be some of you can help me get it right . Can you use cob for the mass or do you have to use cement ?

Paul Tofflemire : This is an easy one, Go with the cob. First, completely plaster your piping between 3/4'' and 3'' using clay slip to help join up one batch of cob
with another!Then you can infill with any heavy, dense material that you want- rocks, rocks with orebodies in them, old broken up Concrete, (we call it urbanite)!
It will make your job go faster, again clay slip is your friend paint it on, or dip the next piece, you don't want any voids or air bubbles, start at one end working
to the other end about a 1/4 to a 1/3rd the depth each pass, the only smooth coat needs to be the last ! and then only so it looks level but drains well off of the
top !

Comeback here often, with 22,000 fellow members, you should be able to come here 24 / 7 and find someone who wants to talk about what you want to talk
about ! Big AL !

Thanks everyone can I use steel as the same as bricks? I work on heavy equipment and all ways have used parts or does rocks and bricks give off more heat?

Paul Tofflemire : save the metal bits for the Cob Thermal Mass. Check out the article in wikipedia on High Temperature Hydrogen Attack, not even stainless
steel is safe. Also we want bricks that reflect ( most people here in these forums say Refract, you will see both ) most of the heat back into the Combustion
Zone, rather than materials that absorb and transport the heat energy away ! You can google ''The Engineers Toolbox'' look for specific heat of materials
and heat transfer !

I was exposed to all this at a younger age, if I had to learn all this now I could not do it ! Big AL !

Ya you could Al its all about the willingness to learn. I know this first hand

Wow, with all this talk about greenhouses with RMHs you'd think the problem of moisture and cob would be covered better. In all of 5 pages, the question was brought up several times, with no real answers. Is this to mean that its not a problem?

Ernie and Erica, in a vid on youtube, suggested rubbing the cob with soap to protect against drink spillage. Would this be a valid solution in a greenhouse for the surface of the cob? Perhaps oiling the surface somehow (another vid suggested linseed oil as a surfacer).

Matt Sorrells : A late Welcome to Permies.com, our sister site, richsoil.com, and a Big Welcome to the Rocket and Wood Stoves Forum Threads ! With over 22,000
fellow members world wide you should be able to come here 24 /7 and find someone who wants to talk about what you want to talk about !

Mold, mildew, rusts, musts, and other bacteria and fungi which are hard to keep in check in greenhouses and are a symptom of high humidity Green houses, a green
house operator who tried to move from the arid conditions around Phoenix to the Atlantic north east or Pacific north west would probably lose his shirt, ( the guy
who figures out a peat pot with the right inoculation of fungi, for local conditions could do no wrong )

Inside a greenhouse you are trying to provide your Rocket with short, small dust dry wood in an environment often dripping with water, this is a big issue to me !

I like high Benches for grow beds for starting seedlings so i don't have to bend over very far, just a little slope will let water run off, and we use lots of plastic
sheeting recycled from the skins !Near here is a green house setting empty with clay and sod Raised benches that never saw a Rocket Mass Heater, the owner of
mixed oriental heritage always applied a yearly wash/coating of egg whites on top, and The bench often had water standing on it !

I think all that is needed to sustain the thermal mass is due care, certainly there is nothing wrong with your plan, Ernie also said he likes to use glass bottles to
polish the final coat not exactly unlike floating the surface of a recent Concrete pour ! RMHs are very new in Greenhouses, come back and ask again in 10 years,
everyones experience will be different for the craft ! Big AL!

Has anyone ever used a rotating chimney cap on a mass heater? I was thinking of making one. Would it make a better drift ?

Paul T. : My Opinion is meh! Those I have used had already been installed, as they a little pricey for me, if they are installed on a chimney that is tall
enough to catch the breeze then generally they are no longer needed, Once they are installed you can look at them and instantly tell when you have a good
draft !

In some locations with a flat slanted roof in a house that looks like 3 stories in the front, and 2 stories in the back, IF- you can get a ventilating screened grill in
the soft /facia of the over hang, the rotating chimney cap is very effective for pulling hot air out of the attic/3rd story !

If used for a ventilation purpose for a small green house I think they would serve o.k. if you have 'good' local breezes during the sunniest part of the day,
securing them to the walls, skin of a green house might be a problem. Plugging them for the night could be as simple as tufting in an old sweatshirt with a pole
to act as a dead man !

If you come up with a good working model share some pictures ! Big AL !

How do you post pictures.?

Here is a picture of my riser hope its right

I don't know if this question has been addressed elsewhere, but I was wondering if the exhaust from the RMH, at least partly, be vented within the greenhouse and not out. After all, this would achieve 100% efficiency AND it would increase the CO2 which plants breathe.

Roman Pravak : Because we had it drilled into our skulls in elementary education, we know that green plants produce Oxygen as a waste product while making
sugars! This has been batted around a lot !

On really dark cloudy or rainy days, or at night they need to use Oxygen, their greatest intake of Oxygen and venting off of CO2 happens during O'dark thirty
and they do not need more CO2 then !

Do you remember the movie Apollo 13, The most famous line was 'Houston we have a problem' . After an onboard accident crippled their craft the 3 astronauts
had to attempt to return to earth, and were both short on power to sustain them and their craft, but their oxygen scrubber was damaged, and they had to field
improvise a scrubbing system before he rising Co2 put them all asleep in a coma that they would never wake up from !

Like the story about being ever vigilant to stop the terrorists, you have to be right every time and the bad guys or excess CO2 only needs to happen one time !

The plants really do not need it that much, and you only get to be wrong once. ! More than a few of your fellow members have experimented with Chickens, Ducks,
and other poultry living at floor level in greenhouse pens At Night mostly with good results ! For the Crafts ! Big AL !

Unless, you stop your burn by dousing it, it is hard to avoid unbreathable smoke at the end of your burn. The coals produce more smoke which is unavoidable as the fire dies down.

Please install a proper chimney; you should have temps of 140° - 160° going into the stove pipe for good drafting.

I'm in a lot of commercial greenhouse operations in a week and they burn natural gas and exhaust it right into the house but only in short cycles. I think that not having a exhaust would quickly dis colour the plastic and lessen the light from the sun. Also when the droplets of water forms on the plastic it will rain that brown staining film down on your plants causing another issue to deal with.Not to mention the health to the people in the green house.

Big Al here are some pictures of the cap I mentioned. What do you think? I have made them before for normal wood stoves and they word well.

Here is the other picture it will turn 360 with the wind

maybe it will work this time

While that style would work fine on a regular wood stove where you have a flue damper that you can close off and you don't care much about cold air falling back down the stack when the fire goes out I think you need to make it a 180deg (2 elbows) instead of 90 to prevent that cold air from cooling the mass.
Also with a 180 you don't have to worry much about wind direction. I have been using one on top of a 13ft stack (from horizontal duct to top of cap) and it doesn't seem to restrict flow as compared to a straight stack with no cap.

John I was thinking of this because of I am going to have a 50 foot mass and was thinking it would improve my draft

Paul Tofflemire : Opps ! I was Thinking about something completely different, and much more expensive !

Does your model, Have a " Lazy Susan Turntable built into it ? I am assuming that the large fin on top is supposed to work ilk a weathervane to keep your caps
opening pointed away from, and down stream of prevailing breezes. You sir are a 'Tin Smith' and probably should look into seeing if you can add in a Venturi
effect ! I think your 'Weather Cap Is Worthy of a separate thread of its own showing a complete build !

You might want to check out the Fine people at Instructables.com, Not only would they enjoy learning how to make a Cap like yours, they have a nearly
foolproof way of breaking down, and laying out the tools, parts, and materials, and the steps to make such a project, allowing you to 'Showcase' your project
with Great Results !

Your project will be peer-reviewed, but Trolls are very quickly ''Put in their place '' ! Big AL !

Big Al yesterday I finised my chimney when I lit a peace of paper and put it in the tee 4 feet from the bottom of the stack it sucked it out on fire right out side on fire . Do I have to much draft ? The rocket is 50 feet from the stack. Is this normal?

Paul Tofflemire : Normal? No, not in any system that runs 50' feet from RMH to Vertical Chimney ! I Think you have been very very lucky !

With such a long system you may yet have some problems when -after a cold night you find that the early sun and morning breezes have combined
and it is actually warmer outside than in, You may have to start a small fire to warm up the vertical chimney to get your system to draft!

(Or open every vent and door, and let the cold fall out !)

Some rich society Grandame is often quoted as saying, ''You can never Be too Rich or too Thin!'', I will add -or have too much draft ! Knowing that the
Original Speakers reaction to the draft would be to get her son an Officers Job in Washington D.C. Big AL !

Late Note : Pictures, and a sketch of your "Storm Cap " Please !

Big Al Thank you for the positive feed back . I have a problem with posting pics. and such. The real problem is I'm not so good with the computer . However I will gladly share the information on the cap I just need to know how to put a drawing on the forum. When I did the test with the burning paper there was little to no wind if the wind gets up will it be a problem?

Paul Tofflemire : I'm gona whimp out on you here ! If you can guarantee that your rotating Storm cap will work 100% of the time, You should never have any trouble
at all ! Big AL

Paul Tofflemire wrote:Big Al Thank you for the positive feed back . I have a problem with posting pics. and such. The real problem is I'm not so good with the computer . However I will gladly share the information on the cap I just need to know how to put a drawing on the forum. When I did the test with the burning paper there was little to no wind if the wind gets up will it be a problem?

Hello. I was able to see your pictures from the other day. Looks like some fine work. I offer the next statement only as summary of my experience with a store bought rotating chimney cap and not trying to assume yours works in a similar fashion.

We installed a rotating chimney cap on our RMH with the following logic: We were having issues with back draft and thought that a rotating chimeny cap would serve to 1. stop the draft and 2. increase the draft while wind was blowing. The rotating chimney cap did both functions perfectly. We have not had a single backdraft and the draft was increased as the wind was blowing.

However, there was a slight problem. While the wind was blowing it helped increase the draft while a fire was burning. Later that night, when the fire would go out, the wind would still blowing and the draft was now cooling my mass that I worked so hard to heat! A fellow permies member that pointed that out! Kudos to them! You should consider if that will ultimately help or hurt your cause. In my case I stopped the rotating of the cap and still had the desired effect of stopping the back draft. I am sure a number of solutions could be worked out to stop the draft after a fire goes out.

Amos Thanks for the input I can see where the increased draft will cool the bed off . I have covered the burn chamber after the fire is out but I think the cold air may still come down and cool the bed. I have an other problem my temp leaving the stack is over 140 F the pipe in my bed from the burn chamber to out side is 66 feet long. I am still in build mode and the pipe has no cob or stones on it yet. Should the bare pipe give off a good amount of heat when its burning the pipe is about 200F but doesn't seem to give off much heat. Is it possible I have to much draft? The top of my barrel gets red hot more the 930F that is as high as my temp gun goes. At the bottom of the barrel its about 520F. Shouldn't the pipe be hotter? My pipe is 8 inch and is straight for 50 feet than goes up 16 feet or so to the rotating cap. Where I live it is very flat and open and the wind gets up almost every day. Can anyone offer any ideas? This is my first rocket so any help would be great.

Paul Tofflemire : The good news is you have much less of a problem than you think you do ! Like most Americans we were brought up in houses predominately
warmed by a Fossil Fuel Fired Forced-air Furnace. Actually, air is a much better insulator than a source of heat, Think down jacket ! Without a fan
to move the heated air our whole house gets cold !

Once you Get your system Cob'd-in The Combination of cob, heavy dense rocks and 'urbanite' will soak up the heat energy much more effectively, and the heat will
warm your room with direct radiation, warming 1st the objects in direct contact with it, then objects close but farther away, and then as the air in your living space
gradually takes up the heat energy from the other objects in the room, you will find that you are actually warmer setting there at your Rocket Mass Heater RMH at
a much lower air temp in the room than you ever were before!

You will have to go through the slog of installing your RMHs Thermal Mass, and pumping enough heat through it to get it to dry out, and this will take a lot of heat,
and a lot of wood, This brings us back to the Rockets demand for very dry wood.

Besides having to dry out the wet Cob, you have the Moisture content of the wood, and the products of the highly efficient Combustion of our fuel wood is Carbon
Dioxide and Water Vapor, as a percentage of the original weight of your well seasoned wood the total water weight is about 20%, so you have to process three (3)
streams of water, and you only really have control of how dry the wood is that you have in your fire right Now ! (Once you get every thing dry, you will suddenly
be using much less wood - just like you were promised in the beginning ! )

Immediately after the Hot exhaust gases enter the Horizontal run, you have a condition called laminar flow, ( I think it should be called laminar non-flow!) Here
the Hottest and fastest gases flow down the center of the pipe where your IR Gun can not see them to measure them! As you move out from the center of your
pipe to the inside surface of the horizontal piping, the Flow of gases decreases to Zero. This is actually a good thing that has been planed for in your build !

We do not want to absorb all of the heat in the 1st 15 ' of your horizontal pipes run, rather we want the whole pipe to get warm ! As the Gases cool and slow down
they will also redistribute their heat, warming the whole of your Thermal Mass Bench !

I think you meant to say that your temperature as measured at the Skin of your stove pipe was higher than 140dF Entering the Vertical Stack, this is still normal
-until you get things Cob'd-in!

The actual length of you system is 66', but only the 50 horizontal feet count against you, when you pass a certain point in length of your final Vertical Chimney
-which will be specific to your location, That chimney will add to your draft ! It sounds lie you are already there !

Everything you are experiencing is normal, we have passed the point were one of your fellow members should have recommended going to rocketstoves.com
To Download a PDF Copy $18.oo of the brand new 3rd edition of Ianto Evans' great book, "Rocket Mass Heaters "! I am still going to recommend this to you
simply to have something that you can refers to 24-7, rather than waiting on your fellow members to get back to you !

Alternately you can always go to the top of this page, find the Permies Toolbox, select 'Search' and on the Search page enter a topic into the 'Search field ' and do a
search of all of the 100s of thousands of Forum Threads with-in Permies itself, Membership has its privileges,this is also available 24 / 7 ! For the Good of the Craft !

Think like Fire, Flow like A Gas! Don't be the Marshmallow ! As always your comments and questions are solicited and welcome ! Big AL !

Big Al thankx for the feedback. I have another problem or question do you put cob all the way around the pipe or just on top of the rocks? Another thing I'm having trouble with is smoke back witch I don't really understand how it could do this. I have so much draft that I have to lite my stove with cardboard because if I use news paper the draft just takes it away. I do have the book from Ianto Evans an I haven't found a fix and it doesn't really say if you cover the pipe or just the rocks after you cover the pipe with rocks. I have found that covering the top of the burn tube a little helps a lot any other thoughts?

Anyone here venting excess heat from the rocket In an attached greenhouse into the residence during the day, and using the home's heater to maintain minimal heat levels in the greenhouse at night?

Paul : The plan Cob should be totally wrapped around the Horizontal ductwork, 1st use a paint brush to coat the entire surface with Clay slip and then coat all of
the pipe with Cob, finish sealing all of the pipe with cob, then use more clay slip, paint on as you add the Dense rocks and urbanite into the Cob Thermal Mass.

Without the entire horizontal pipe being Cob'd in, i can see how you can get smoke back that should disappear when you get everything Cob'd in, But i am a little
at loss to explain any other reasons for smoke back, unless the whole Greenhouse is too tight ! Experiment more with ether filling the burn tube with wood to
promote a good air flow or partially block the air opening at the fed tube, mostly it is a matter of learning by ear what your RMH wants !

William Bronson : One of the great benefits of the RMH is that for 3-5 hours of an automatic tending of my RMH with very little thought to my task, I then get 8-12
hours of heat radiating off of my Cob Thermal Bench. This should cover the night and early morning!

If I had had a Couple of Sliding glass doors that opened onto a south facing patio, or deck, and I then converted the whole thing into an attached green house, I
can see Being able to reap the benefits of my Solar gain and my Radiated heat from my RMH. Even finding a way to use The Houses conventional furnace for
more heating than just My house in a Crisis, but remember Even if I had Lots of Young seedlings Right now, in the middle of February all they need is a greenhouse
in the 40s, and row covers to trap my RMHs heat right down at the seed beds !

Big Al I have cobbed in my pipe and put rocks around it is there a wrong way of doing this? I have the cob dry but I don't get a lot of heat from it the odd rock will get warm and the more I put on it the less heat I get. Should the cob be dry before the rocks are placed? The top of the barrel gets to 940F and after 2to3 hours the cob is only 120F Shouldn't it go to 300F

Paul Tofflemire wrote:Big Al I have cobbed in my pipe and put rocks around it is there a wrong way of doing this? I have the cob dry but I don't get a lot of heat from it the odd rock will get warm and the more I put on it the less heat I get. Should the cob be dry before the rocks are placed? The top of the barrel gets to 940F and after 2to3 hours the cob is only 120F Shouldn't it go to 300F

As long as the cob/rocks in the bench have no air pockets around them your good. You should probably have a final layer of only cob on the bench, and not have any of the fill rock exposed. Although not that big a deal.
Lastly the bench if all the cob is dried out will never get to 300. I think maybe 150deg is tops, more likely 130-140.

Bump !

Here is a youtube video I saw a while back that is spot on what I am wanting to do eventually.



It is basically using a rocket stove to heat up some copper coil that is wrapped around inside the chimney. The copper coil is filled with water and as it heats it rises on it's own and creates a circulation to a water container of any wanted size. I am betting that one could build a large chimney within OR outside the greenhouse and have several copper cores up through the chimney extracting heat to multiple water containers. I would recommend running the copper pipes through the top of the water containers instead of through the sides for low maintenance purposes. Then insulate the top portions of the containers so they release their heat a little slower. This way you basically have a rocket stove heater with water mass. If you use cob to build it then great. However, even concrete could be used inside of 5 gallon bucket molds and built for around $12 a section. You could have a easily stacked 6ft chimney with 3 copper core sections for $36(complete guess on the estimate).

You can even get artistic with the design and make the chimney a tikki statue. With each section of the chimney being a different part of the body. Here is a tikki rocket heater.

http://cdn.instructables.com/F2C/I2FY/HKM8OLXQ/F2CI2FYHKM8OLXQ.MEDIUM.jpg

Marty M : It is not clear from your thread if you clearly understand the differance between a Rocket Stove and a
Rocket Mass Heater RMH, The Rocket stove as built can not reach its highest efficiencies around 600 degrees where
the wood gas products can be burned without producing Creosote. The maximumum temperature the copper tubing
can reach is 212 degrees, above that temp the Water in the system will flash to steam, forming a type of high temp
hydro-lock and the copper will deform or even melt .

Regular Portland Cement Can not be used within the Combusion zone of ether the Rocket Stove or the RMH !

The high temps will destoy the chemical/mechanical bonds of the 'lime' content of this type of cement/concrete !

Other types of Furnace Cement are pricey and experimentation with this type of Binder can get expensive quickly !

I think the original poster of the you-tube video did a good job of explaning the way he plumbed the copper tubing,
the cold water drawn off of the bottom of the 5 gal pail displaces the lighter hor water and the hot water flows by
gravity through the system and dumps the hot water back into the bucket at the topof the pail .

This thermo syphoning action is automatic and does not require the pumps to curculate the water from the bucket
to the fire and back to the bucket !

Have you been to rocketstoves.com to get your pdf copy of the new 3rd edition of Rocket Mass Heaters ?

Also please take that you see on you-tube with a large grain of salt ! there is a lot of crap out there ! Hope this is
timely and helps ! Big AL !