Rocket stove for greenhouse

I have built a rocket stove with cement blocks and firebricks and a 55 gal barrel. It runs like a champ. I am trying to use it as a heat source for my small attached greenhouse. I have two 6" pipes connecting a hot air gathering unit (A 55 gal barrel open in the bottom suspended above the stove). It has a couple of fans to move the hot air to the greenhouse. Right now the exhaust from the rocket stove goes up an existing chimney. The top of the stove barrel get to 700 degrees F which is great. The problem I am trying to solve is how to move more heat to the greenhouse. I live in VT and it is currently 10 degrees and even my kale is shivering. I understand that most rocket stoves move EXHAUST air for heating. I am a little reluctant to do this. Does anyone know what portion of the heat from a rocket stove is released through the barrel vs how much heat is moved through the exhaust? Am I expecting too much?

Doug Varney : I am a little concerned about the longevity of the concrete blocks that you say you used in the construction of your rocket burner, can your send
pictures or a sketch of your Concrete Masonry Units C.M.U.s shapes, and the way oriented and locations ?

Your rocket mass heater RMH, is working as well as any RMH, and only so much can be radiated off of your 'double barrels ?' a regular RMHs Barrel is sealed
down against the rocket burner and radiates about 40% of the total heat produced by our rockets very efficient high temperature burn.

Unless the hot exhaust gases are further channeled through additional stove pipe (irregardless of whether that piping is covered with a Thermal mass), all of
the rest of the heat must go up the chimney ! ~ 60% ~ !

It rather sounds as though you have quite independently created a Rocket burner with an attached bell. Even if that is the configuration created, the bell
would better serve you if it were located within the Greenhouse and not just trying to heat air that you are then trying to push into your green house, if that is
what you are doing, you are probably (My Best Guess ) losing close to 20 % from one location to another !

Without sketches of your layout and some pictures, it sounds as though a change to what most members here at Permies.Com would consider to be the more
conservative and traditional route should double the amount of heat you are getting out of your wood !

This does not include the benefit from heating ether the floor, or earthen raised benches ( think about how much better your back would feel only bending over
a little, not a lot hundreds of times a day) and having the air just at the height of your young plants protected by the stored heat in your earth !

Please get us some pictures of your existing layout, because this is a cold early winter, we need to find a simple way with short easy steps to increase the
amount of heat you are able to make use of ! For the good of the craft ! Big AL !

It sounds like your basically using your RMH barrel as a heat exchanger and capturing the heat with another barrel. If you secure the top barrel to the RMH barrel and pump air in the bottom with a blower from the greenhouse as a cold air return then maybe insulate the top barrel and the hot air supply duct back into the greenhouse off the top of the barrel you might have something there. Depending on how well the greenhouse is insulated (besides the south facing part{the term escapes me}) you could heat it pretty well. However unless you plan on running the RMH all the time, you need a mass to store and radiate heat when you aren't. I think water barrels as a mass storage medium in a greenhouse is the way to go.
If you could heat water in the top barrel (By any number of methods) you've added and circulate it into barrels in the greenhouse (Insulate the heating barrel and the water lines) you'd be really good to go.
You could even do both heated air and water. The bottom line though is you can only produce so many BTU's of heat with your RMH. You'll use some as radiant heat off the barrel, some is stored in a mass, and whatever is left (hopefully very little) goes out the flue pipe.

I think all of your observations ring true to me. My greenhouse is small, was built in the late fall, and is a work in progress. It does have foil faced foam insulation in all non-transparent surfaces and hay bales on the outside as additional insulation. Because it is small, I wanted to use the existing rocket stove in my workshop and try to move in the hot air. I think this current setup is RMH beta. I have a feeling that next summer I will build a heater inside the greenhouse and run the exhaust under the plants with some sort of thermal mass. I have lots of food grade 55 gallon barrels that I may lay on their side and run the exhaust gasses in 6" steel pipes around them as a heat sink. I will want to go through one winter to see how much thermal gain I can get from the sun. Here in VT, November and December are often dark and cold. Jan and Feb can be cold but sunny. I am hoping that the bright sun can carry a good portion of the heating needs. I would love to work with cob but our subsoil here is hard pan and, though impervious to water, may not contain enough clay particles to set up. Looks like I have lots more experimenting to do but that is what I live for.

Thanks for you kind advice. I will keep checking back with you all if more suggestions are made and I will provide some pictures if that would help.

Regards

Hi Doug; I'm in my first winter with a rmh in our detached greenhouse. Bottom line is we love it! The radiant heat off the barrel is what brings the room up to people temps, the long term heat off the mass is what keeps the plants happy. I use solex as my greenhouse covering so i get a small r value out of it, but the mass is what makes this so nice! I am in northern montana temps recently have been 0-5 in the overnite and 5-15 during the day, I relight the stove around 7 am and we keep it going all day (still uses very little wood) the room during the day can be anywhere from 55-70 + degrees we stop feeding the stove around 10-11 at nite and the next morning it will be 42-48 degrees!!! This week temps are warm 25-35 ,last nite it stayed above freezing 33, stopped feeding fire around ten last nite, temp this morning at 7 am is 56 degrees! I use a raised bed as my mass with cob and slate as my filler. Would water work better? probably but i have not experimented with it yet. I grew up in new england and if there is no clay in your yard you can bet that somebody nearby has more than they want. talk to local farmers or the county road crew, somebody will know where a clay pocket is.

I have a question. Why is no one just dropping the exhaust from the stove right straight into the air in the green house? The CO2 should improve plant growth and odds are between plants, ventilation fans and air leaks you probably have enough air interchange to keep the air suvivable inside. A CO detector would protect you from that risk. This would be especially true for outfits with bigger green houses that are running inflation fans to keep the plastic stretched. If the stove were in the green house and directly vented in the green house you would have 100% efficiency from the heater.

Doug Varney : as T.R. has said the local highways Dept -Town, County, or State roads Dept, will know the trouble areas where the supersaturated clay soil
will landslide in a heavy rain and need a front end loader to open the road again, or perhaps there is a 5-25' overburden of clay on top of a working gravel
pit! If that fails (rarely) try a local excavation contractor, he not only knows where the clay is but has an idea of how clean and how thick it is!

To talk directly with the boss tell them you are looking for clean fill for your property! As he has to pay to remove all the material removed from the excavation
he is looking to haul it the shortest distance, if you tell him you are willing to come and pick up the overburden clay yourself he will be your new best friend,
show up at the end of the day or at its beginning to the soil samples and be prepared to do a soil sediment test ! (Google IT )

If the results seem promising, make up some practice bricks !

Air quality yes everything you say is correct, however a few things to consider !

Did you ever see the movie Apollo 13 about the 3 man crew who had to abort a planned trip to the moon after an onboard accident, they were left with little
power and oxygen! The most famous line from the movie " Houson, we have a problem !! "

The failure of the on-board carbon dioxide scrubber was creating the situation where Carbon Dioxidecould reach levels where it could become a
powerful poison, putting the crew asleep, a sleep from which they would never waken ! A Carbon Monoxide CO detector will not detect the presence of Carbon
Dioxide, CO2, No matter how strong the concentration of CO2 becomes !

During the day with 'normal daylight', Plants are Oxygen producers, however at night they switch and become Oxygen users, a high presence of Carbon Dioxide
CO2 at that time actually hinders the plants further growth ! For the good of the craft ! BIG AL

Late note : As the guy that used to get out of bed on a ''NO Heat Call'' at 4 A.M., I have had the experience of totally frozen hay bails that quickly equalized
their surface temperatures with the entire mass, actually transporting the cold through the entire mass to the temperatures of the Air against the skin of the
building, basically providing Zero protection against the cold ! For Any insolation to work, it most be protected from All Forms Of water absorption, and that
includes water vapor released days before from (then)warm moist ground ! Hay absorbs water out of their and becomes non-insulative !

Hope this is timely and helps, for the good of the craft, Thinf like fire, flow like a Gas! Don;t be a Marshmallow! All questions/comments are solicited and welcome
PYRO - Magically Big AL !

What great information. Thomas, you have convinced me to move my rocket stove into the greenhouse and damn the loss of space. No amount of space compensates for frozen plants. Since my dad was an agronomist, I know about the day/night CO2 give and take. I doubt the greenhouse is quite that tight. That being said, I will run the exhaust back and forth under the plants but I won't be anal about small leaks. Is it important to run the exhaust pipes in a slightly upward direction to encourage draft or does the final vertical stack at the end of the run through the roof provide sufficient draw? You might enjoy the fact that I am reusing #10 steel cans as the pipe for the exhaust. I find that the new aluminum suretape works well to bind them together. I will use conventional stove pipe coming directly out of the barrel but expect the temps to have cooled enough to keep it safe. I also will be running the pipes in between some 55 gallon barrels of water as a heat sink. How important is it to insulate the floor under the exhaust pipes and barrels? I may just do that anyway to be sure. re: the hay. You make an excellent point. I have somewhat encased the bales in heavy plastic. I will check them for moisture as the winter progresses but it gets rather dry here at -15 F.

Ironically my family used to own a farm in VT where it was nothing but heavy blue clay. I may take my pickup truck down there next summer and try to beg some material from some house site. I would love to work some of that beloved ground into the project.

Thanks again for such a fine response to all my beginner's questions.

Doug Varney : Much of the Blue/blue gray clay is crap, technically the problem is a lack of Alumina-Silicates, a local potter 'might' know, or because of its low held
esteem (s)he may just assume its crap! The only way to tell is to try and make a brick out of it and see! Try ---> www.traditionaloven.com/articles/101/ < also
try going to the 'pclould' at the top of the page is the Permies ToolBox, clickon> 'Search' which will take you to a separate page where you can enter a subject into
the 'Search Field' and do a Permies only Search via Google , or > the whole web search !

While you are at the Permies toolbox you can also upgrade the information shared to the world with your name look at your name and L@@K at mine , At the
Toolbox clickon> the "My Profile'' button and follow the prompts to add a general location and climate zone, it will better allow your fellow members to help you
with questions and it puts you out there where you are moe likely to connect with a near neighbor with more rocket experience ! Big Al !

Doug; I asked the same question about sloping the pipe and the answer was no , your vertical rise at the end will create all the draft that you need. That is what I was told, by observation i think that a very small slope would help allow condensation to flow all the way back to your transition area where it would quickly evaporate. I personally put a layer of hay filled cob down for my horizontal pipes to lay on as an insulator from the ground , i'm not sure if you need to but it made sense to do it that way. Were you planning on surrounding your water barrels in cob ? Tom

Thomas,

I am currently planning on insulating the floor of the GH with metal roofing to isolate from moisture then 4" of cellulose. The barrels will sit in this with the 6" "flue" along the sides of the barrels. Cob will come later if this doesn't work.

Hi Doug
I used #10 cans to build my first rocket stove 3 years ago and they lasted a week before they totally disintegrated but I used them for the burn chamber, heat riser and exhaust flue! You are obviously not doing that but you might want to keep some check points where you can watch them to see if they are getting brittle which is a sign they will crack and fall apart. Best of luck. I currently run a side loading RMH with a 12"x12"x38" firebox made of firebrick in my 34x30' shop and I love it. here's the youtube erl.

Update:

I have moved my stove into the greenhouse. The flue is now a 6" metal pipe instead of an 8" chimney. No surprise that I had to shorten the length of my J tube and reduce it's cross sectional area a bit. It now runs quite well. To provide enough residual heat through the cold night, I am going to place a 55 gal drum of water directly on top of the 55 gal drum of the RMH.. I plan on an interface between the two of 20 lb iron weights so that the top of the RMH barrel is in direct contact with the water barrel. I will vent the upper barrel (bien sure) On each side of the RMH I will place two additional water-filled barrels. I will have to see if these side barrels pick up any heat. I might circulate the water among the three IF the upper one gets too hot. Only testing will determine that. I will also include a pipe to the outside of the greenhouse to provide fresh air to the barrel that encloses the wood feed to the J tube. Thanks for the tip about placing a T in the flue pipe to allow for some preheating of the exhaust stack. I will update with more data as the project progresses. Thanks to you for all for the help.

Here are a few pictures of the RH in the greenhouse. The 55 gal on the top full of water and store heat for the nights. The stove gets its air from a 4" pipe from the outside. I fuel it with pallet wood. I had to develop some techniques to prep wood as pallets no longer come apart. Runs like a rocket.