Rocket stoves in Greenhouses , our own forum topic

If you have a greenhouse large enough to add a vestibule to it, you could put the wood storage and feed there, with the burn tunnel running through the divider wall and barrel and mass in the greenhouse proper. I have seen several designs and I think one or two installations like that.

The issue with CO2 injection from a RMH exhaust, aside from health risks to animals, is that there are some toxic compounds in the exhaust, not just CO2 and water. The toxins should be minimal in RMH exhaust compared to woodstove smoke, but not negligible.

The internal diameters of this system are;
burn tunnel - 6"
heat riser - 6"
heat exchange duct - 8"

The base of this thermal mass starts with 4" thick x 12" x 12" chunks of concrete slap as the foundation, then the heat exchange ductwork on top of that and bricks, paver sand fill between ductwork and more of the concrete slab chunks on top of that then I will run a coarse of brick about 4" tall, brick turned sideways then fill in with more paver base sand and then I will finish with a flat surface of 18" x 18" landscape pavers. This mass will ultimately hold at the surface 5 - 55 gal plastic drums full of water for additional mass and heat transfer. We are using chunks from that same demoed concrete as the face of the mass. I have also used repurposed bricks on the face of the mass to give it some dimensional shape in preparation for the top surface of the mass. again using landscape pavers from the big box as the surface of the mass and put them on level. I am building up one course of brick above the sheet metal duct and fill in with paver base. I am thinking that this will give me a solid enough base for the surface in order to hold the 2,282.5 gallons of water in the barrels with zero deflection at the surface. I am also using river rock around the barrel simply for aesthetics. I am realizing something at this point of the build. It is called spacial cognition..... meaning that I sometimes have a challenge seeing in my minds eye just how big or small something will be as the end product even though I use tape measures and levels..... At any rate I am attempting to build in sufficient foundation. We don't want to crush the sheet metal heat transfer ductwork. I am using a mud mix that I call "Cob Mortar". Since I have an abundance of red clay I start with a mixing tub 1/2 full then I add a bag of general purpose sand or .5 cu ft. then I had 1/3 of a $5.00 bag of cheap mortar mix from the big box. Using a hoe I mix thoroughly, good work out. Then I let it set for 30-45 minutes and give it another good mixing with the hoe and shovel. If it was the heat of summer I would use it immediately but I am working in a fluctuating lower temp inside the GH. I have basic brick laying skills nothing fancy but I know the consistency that I am looking for and I know how to put icing on a cake. BTW - I had to stand on a ladder and use the top lip of brick around the fire chamber. With my weight and the surface area of the ladder leg, the brick did not budge, this was about 18 hours later after laying the brick. During this time of work on the mass the RMH is in continuous burn mode and it is working well. The mass is not complete so we cannot expect it to perform to it's full thermal properties just yet but it is beginning to hold some heat.
Does anyone see a glitch or a flaw in the foundation design. I just want to make certain that I will not crush my ductwork since I have this amount of weight to handle above it at the surface.

The amount of straight sand you are using is concerning. Dry sand, while massy, is more of an insulator than conductor, and will not absorb heat from the duct and transfer it to the surface very well. Now as you are in a greenhouse, there may be enough humidity and water in whatever form that the sand stays damp, thus being a decent conductor. The concrete, brick and pavers sound good. The professional heater builders will have to give opinions on the suitability of the clay-cement mix.

Going from a 6" heater core to 8" duct means the exhaust will meander slowly along, possibly extracting more heat than is safe and leaving you with nothing to assist in chimney draft. That depends on your system length and other details.

I thought that I might be cutting my efficiency by using the paver sand. I've only used 3 bags worth so I will excavate that and use it in the red clay/cob mortar. Then I will fill the voids with the red clay instead. On the 6" core to 8" heat exchange duct, there is more. At the end of the 8" HE Duct run I reduce back to 6" at a 90deg bend up for 12' and a 45deg bend to take the chimney out of the greenhouse. The HE Duct is 21' long including 1 U-Bend and 2 clean-outs. My thought on going to 8" HE Duct was two-fold. 1.) I was given about 30' of repurposed 8" duct 2.) I figured that I could create a greater heat exchange by increasing the size at the HE Duct and then reducing the chimney to 6". This duct sizing seems to work fine, I don't think it is impeding the flow of gases or decreasing the available heat. Maybe the 6" straight thru would be more efficient but the 8" seems to work fine. I can't wait to finish all of the mass and get my first burn with a full mass.

The 8" duct will not impede flow, to the contrary, it will reduce the friction loss in that section; it just might be too efficient at heat extraction and leave less heat than is needed for draft. But if you say it is working as is, great! That was a theoretical concern, and experimentation is the best guide to what will actually work in a particular case.

Hello everyone. I'm new to permies, and glad to be here. Ex-NYer, living in the UK. Tried to send a post the other day, but seem to have failed. Since it's been three years since the last post, I'm wondering whether this is an active forum?

Anyway, here goes again. I have a 12' x 8' greenhouse in zone 9, and would like to put a 6" core system in one end of it, run pipe under the soil down the length of the north long bed, across to the south bed, back up that bed and out. One of the main uses for this heater will be to rescue my poor tomatoes, peppers, eggplants, and melons in July when we often get a couple of weeks of rain and chill weather, just as everything's struggling to ripen. (I hear that happens on the west coast of the USA, as well).

I have a couple of questions. 1) Could I run 6"metal pipe under a greenhouse bed and expect it to last more than a season or two in the humid conditions? I'd love to use clay drain pipe, but I'm not sure I can find what I need for a reasonable cost. Can't use cob underground, so I was thinking I would lay metal pipe in sand and cover it with a little soft-brick tunnel, to better absorb and distribute the heat. 2) What temps should I expect in the pipe, closest to the manifold?

I've attached a picture of the greenhouse.

from what i have read, the temps at the manifold can be 4-500*f.

have you seen the half barrel bench systems by matt walker? seems that would make a great base for grow beds.

The half barrel bench suggestion is a good one. Ducts with the bends required would about max out the length for a 6" system, and in those conditions I think you need all the oomph you can get. Especially in summer with minimal temperature difference to drive the draft, half-barrels running the distance and fully connected end to end would give good flow and maximum heat transfer surface.

Thanks, ronald, for the note on manifold temps, and to both you and Glenn for suggesting the half barrels. I do remember seeing photos of them somwhere. Not sure have the space for them though. One of the beds is going to be 60cm (2ft) wide, and the other 80 cm (31 inches), and just about 60cm/2ft deep. Hmmm. Spreading the heat out would be a good idea, though. Perhaps small barrels? ... I do wonder about all that metal in that damp environment, though. I should think it would rust out in one season, and leave me with a lot of iron flakes in the soil. The barrel over the heat riser, too. Surprised not to have read anywhere that others have had the problem.

You make a good point, too, Glenn, about the lack of temp difference potentially causing a problem with draft.

Thanks for the ideas!

Standard 55 US gallon barrels would fit but might be too large for practicality in your situation. There are smaller barrels made, and they might work for you. I agree with the notion that steel barrels in the growing beds might rust out. Half barrels are a simple way of doing the job, making a structural arch in a cob bench, but you can do the same thing with old bricks or cement blocks and concrete pavers for a roof. The important part will be that the cross section is large enough that the gases inside can slow down and stratify with the hot gases at the top.
This may be a side benefit of a bell in a greenhouse bed, that the hot gases will be concentrated at the top, rather than conducting equally to top and bottom of a duct.


The barrel over the heat riser should be much more durable, though. As long as you don't spray water on it regularly when it is not running, the outside should last as well as any steel tools you keep in the greenhouse, and the inside will be protected from damp.

Glenn, I recently discovered that those 55 gallon barrels are called 45 gallon barrels here. Whew! Was wondering why I couldn't find any of the right size. I could fit one in the corner where I now have an equivalent sized water barrel. I'm now thinking about building a mud batch box, as produced by the experimenters over here:http://donkey32.proboards.com/thread/850/mud-batch-box). Small, cheap, and powerful. I hope! As for steel, I don't leave any tools in the greenhouse. The climate is just too damp. Stove paint would protect the barrel somewhat, if it can resist the temperatures. I'm not sure how I can resolve the problem of needing 90% of the heat in the ground. Thanks for your help. It's much appreciated.

I came here from my initial thread
https://permies.com/t/53493/rocket-stoves/rocket-mass-heater-greenhouse

discovered here a lot of info, thank you guys.
Please if you dont mind, can you help me further to develop RMH? If possible in separate thread, to not mix all the things

Thank you

Hello

French newbie here both in greenhouses and RMH.
Just moved from an unnice foreign country to southwest of France and bought a relatively big piece of land.

My wife (asian origin) and myself would both like to build a large greenhouse. From her side to cultivate asian veggies and from my side to put my 10s of orchids in a place where I can set up a very humid environment which allows me not to water them every 2 days ...

The greenhouse is ongoing. It's gonna be 41*28 ft hence around 1150 sqft. The northern side will be a insulated concrete wall. South side will be 5 large double glass windows. Roof and small sides will be made of 32mm polycarbonate. Structure will be made of wood.

Problem is I need to heat up the baby every night during october to march/april. Winter temperatures here are around freezing point and days are very short. At night, without heating, inside temperature will probably go as far down as outside temperature. Which is totally incompatible with my orchids and all the delicious veggies of my wife.

Last point is: part of my land is a forest and since I am bringing down trees for safety reasons, I will be the owner of 50-70 cubic meters of wood. During the time requested to to dry it (2-3 years), I have access to 1 year supplmy of already dry wood and I will have to buy 1 year supply.


So after reading a lot here and there, I decided to build a batchbox rocket stove mass heater.
Here are the main points:
- I want a batch box because due to our activity we won't have 2 hours to spend each day to maintain a J tube RMH. One big batch and refill after 30 minutes is what we would like to achieve;
- As I don't want to fiddle, destroy and reconstruct the "beast", I want to go for a riser made of refractory bricks;
- I prefer to use bells instead of flues (is it the right word ?) as they seem to create less smoke problems (they are more lenient on bad design ...)
- as I need to heat up a large poorly isolated room, I was thinking about a 10 inches batchbox model. Is it too big ? Anyone has plans (exact dimensions for such a big one ?)
- the RMH will be in the center of the northen insulated wall and I would like to have 2 series of bells running on each side of the walls. Hence I need to split the hot air coming out of the riser in 2 to feed the bells on both sides. Has anyone tried this ?
- the bells will extend 5 meters on each side of the central batchbox/riser structure. I would like them to be low and long rather than tall with a small foorptint. Like that, we can germinate our seeds on the warm bankets. Lets say the bells will be 1m tall, 1meter deep. Do I need to separate 3 bells into the 5 meters or 2 bells will be as efficient ?

I drew a very bad sketch of the design that I will post tomorrow. In the meantime, all your comments are more than welcome !

Have a nice day everywhere on planet Earth !

JY

Here is the (very rough and poorly drawn) scheme of what I have in mind.

have no info about rockets, because im looking into implementation for my geodesic greenhouse, too
but one note, what wood and of what dimensions will your greenhouse construction would be?
i used 50x50mm .. it is good, but because of humidity it will not last long, i guess. Once it die i will make Alu frame

I will be using 150*150 mm treated pine pillars (2.5m tall) for the vertical elements.
Have not yet decided what to use for reinforcements and roof structure.

they will be coupled with armored concrete of the "foundations" (as we call in French) by metallic screwed supports.

++

JY

Hi everyone,
So I'm new to these forums, although I have been checking out this and other websites for a while.
My wife and I have built, this summer, a small green house/well house. its only 15'x10' (100sqft of greenhouse, 50sqft of well house) and have incorporated a rocket mass heater to extend our grow season.
primary construction is 2x4" timber and plywood with batting insulation in the walls. 3 sides are double paned windows and the roof is double layered poly on outside and single layered poly on underside. All of this has been done a SMALL budget (total cost of approx. $500 for greenhouse and RMH) nearly all materials are recycled, begged, borrowed or stolen, well not stolen just bought really cheap!!!

main reason for my post is I'm having issues with the RMH. when first lit it really roars for probably the first 10 - 15 minutes and it gains temp quickly. but soon after it seems to dampen down and unassisted will go out. I've gone through the heater again looking for air leaks, done some leak tests, found a couple of small ones and have rectified but to no avail!!! So I'm now concerned ive got a fundamental issue with my design.
As a temporary solution I have added a duct fan at the end of the system to increase the draw, which causes 2 issues.
#1 kinda not the point of the system in the first place!!! I'm trying to reduce electricity consumption in the well-house with supplemental heat not add to it.
#2 the fan actually draws too much air through not allowing the gases to burn off properly.

At first I was impressed with the temp figures I was getting, compared to our in-house wood stove. (over 400F at the top of the outer tank, and close to 200F at the start of the exhaust) but on replection this is not so good compared to other RMH, this is also using the fan to get super draw.

So here's some details of the heater. mass is just sand, may switch to cob if we get running right.
I used plans from Zerofossilfuels to build the unit, primarily as the materials I had to hand fitted his design and the size of our greenhouse didn't need anything bigger (I hope not anyways!)
attached is scale drawing, courtesy of ZeroFossilFuel.
The exhaust is 4" singlewall duct and is a total of 20' horizontal run then exiting to a 6' high chimney. there are 6 90 degree bends in total. see attached pics  

From doing some more reading I have 2 concerns, are my gases cooling enough to get draw and reburn. and is the gap between the inner wall and outer wall sufficient.

Sorry this is all a bit garbled, just wondering if anyone has any ideas

Snipped and posted for easier discussion:

Generally the first culprit to look at with the symptom of starting fine, then stalling after the burn gets going well, is insufficient insulation around the riser. You need a strong heat gradient between the riser interior and the barrel (downflowing) space, and if the bricks heat up and radiate to the barrel space, that "pump" is reduced. An 8" duct stuffed with fiberglass around the bricks will have next to no thickness near the riser corners, and not much insulation overall. 2" airspace all around the riser is plenty for a tiny 4" system (actually what you have is a 3 1/2" system) so you could go to a 9" duct and get significantly more insulation.

Your uninsulated feed tube and burn tunnel will leak heat and this effect is much more important for a small system than a regular sized one, making it much harder for it to get up to good operating temperature.

20' horizontal for a 4" system is probably near the maximum it can handle, but you also have to factor in the bends, which reduce the allowable duct length. For larger systems, 5' per elbow is the standard deduction; I'm not sure what it should be for a 4" system, but even calling it 2' per elbow subtracts 10' or so from the length capacity. In other words, your system as built is not likely to draft well and strongly. A 6' chimney is not much, but might be adequate for an otherwise strong system. It should rise at least a couple of feet above any nearby roofs in any case to avoid smokeback in case of adverse winds. Do you have any insulation at all on the vertical chimney? It needs to stay warmer than ambient to give draft, and 20' of 4" duct is likely to leave little leftover heat.

Stepping back for an overview, a 4" J-tube system does not seem like the best choice for a greenhouse where you will not be spending most of your time. The tiny feed allows only a small amount of wood at a time, and will need to be fed every 10-15 minutes or so. It will not put out a lot of heat, possibly enough to keep the space warm while running, but likely not enough to charge a mass for coasting overnight when it is coldest. I suspect you will want to upgrade to a stronger system after some experience with this one.

A 4" batch box core is capable of putting out heat twice as fast as a J-tube, and holds much more wood per load. My recent experiment mocking up a 4" batch box core suggests around a half hour per load, so two loads of batch box would equal two hours feeding a J-tube.

Thanks Glenn,
I have not looked at the batch box systems so something new to investigate.

Currently I'm getting about 45min to 1 hr before refueling, I'm burning 2-3' lengths of birch lumber, but as you say, if I'm not burning at optimum efficiency right now I imagine that time will reduce.

You have given me lots of food for thought,
However - if I understand you correctly
Even if I were to increase insulation around the riser, add some insulation around the burn tube and feed tube and insulate the outside chimney I'm probably still not going to get enough heat for the mass?

Currently the barrel is in "open air" i.e. it does not have any mass built around it, I did this to allow easy access should I need to take it off (kinda lucky by the sounds of it!!!). If I am to continue down this route would it be better to encase most of it in mass or to leave it in the open air?

Again, by using the sand as mass, I have the opportunity to reduce the length of ductwork, which may help a little, as well as increasing the height of the external chimney.

Once again, thanks for the input.

Another thought Glenn.

As I understand it, from ZeroFossil, The dimension ratios are critical and presumably the smaller the system the tighter the tolerances - Is this correct?

Reason for asking is could I increase the size of the feed tube, from 3.25x3.5" to say 5x3.5", without increasing the riser tube? or will this total kill any draw I have.

Zero is correct in this; if the feed tube is significantly larger than the burn tunnel or riser, it will have slower airflow, and will not strongly draw heat and flames downward, potentially making smokeback or even flames climbing up the wood more likely.

If you have only smooth lumber to burn, it may work to have such long pieces, but any natural sticks or logs are likely to catch and hang up at some point if they are much taller than the feed tube. This could make the fire go out, or worst case have burning sticks fall on the floor.

Ernie and Erica actually just added a set of greenhouse rocket mass heater plans to their digital bundle - you can get three damp-tolerant designs, along with heaps of other digital goodies (rocket mass heater plans, ebooks, etc.).

You can read about it all here.

One thing to be aware of is excessive heat. I failed to understand certain basic premise of greenhouses in building my first two standard full-scale hoophouses. Like the fact that a small humidifier is paramount to saving money on electricity. And that a fan enables the ground temp and the air temps to approach parity while encouraging the baby plants to breathe. Bad engineering (aka: lightweight 3/4" PVC,) enabled snow and ice to clobber both of them. Standard radiant heaters proved absurdly expensive and temperature control involved opening the door for a bit two trips or so per day. By the third iteration I came up with a novel split-level design that looks like the United Bank Tower of Denver, with a vertical strong-back divider which enables us to open the lid and let heat escape in the Spring. In Summer, the front flap rolls back and the process starts all over again.

Running a RMH vent tube parallel along this division seems like a phenomenal approach to consider. That said, a triple-stage high tunnel affair would also deliver striking benefits, whereas the centermost third could be warm for semi-tropical species, and each end module could serve separate functions, first the entry vestibule- fire station, and at the far end, plants which need less tending overall.

Best of all the greenhouse has come to serve its greatest function as social gathering space, and of course we get crystal pure salads all winter. Like I said, excessive heat is something else to consider.

..contd:

Joanna Sheldon wrote:Hello everyone. I'm new to permies, and glad to be here. Ex-NYer, living in the UK...  I have a 12' x 8' greenhouse in zone 9, and would like to put a 6" core system in one end of it, run pipe under the soil down the length of the north long bed, across to the south bed, back up that bed and out. One of the main uses for this heater will be to rescue my poor tomatoes, peppers, eggplants, and melons in July when we often get a couple of weeks of rain and chill weather, just as everything's struggling to ripen...  I've attached a picture of the greenhouse.

THEORETICALLY, (and let's face it, for many of us this will remain the case until we are knee-deep in our second or third build,) one must consider a very short list of basic physical realities are at play here. In direct answer to Joanna Sheldon's concerns, it appears the addition of a RMH––as a retrofit––is not particularly appropriate for this purpose in a greenhouse of this scale. It should be bigger.

Below(?)- I've proposed a potential three-stage edifice, with two additional structures placed on either side:  Section 1) Vestibule & firebox, serves to buffer the incoming thermal/hydro exchange. Section 2) is the protected core, (as shown) and, Section 3) is a workroom with supplies, starters, seed bank, table & chairs, vertical growing section, fan ducting, etc.

Consistently, any greenhouse is a means of harnessing direct-gain. Sunlight hitting the brick foundation, (and specifically in this case, it's supporting back wall,) OUGHT to be harnessed for use WITHIN the total solar envelope. Paul refers to systems utilizing "annualized thermal exchange," which could get quite complicated when truly engineered to reap every potential watt of energy. But, just for the sake of argument, let's say the RMH ran the entire length of that back wall, INSIDE the home, where this excess heat is (normally) actually needed. And, let's say that with a single-lever you could re-direct all or part of the flow of exhaust INTO the greenhouse.

Moisture 'Holds' Heat:  Nice fluffy soils, in combination with gentle air circulation account for around 40% of our nighttime winter heat appropriation, and more so on mild days. Plants like peppers and tomatoes contribute a lot of transpiration, -breathing heat and moisture from our clumpy clay-rich, 51-degree soil into the space. Air circulation, IMHO, cannot be emphasized enough when dealing with 'boggy' conditions.

Light=Heat: Let's say you added a multi-function water feature. A long pond or shallow reflecting pool running OUTSIDE along the south wall, might reflect a lot of shimmering light into the space and accelerate growth. In my case (z3) this water feature could serve equally well INSIDE, water potentially circulating between channels with a fountain to disperse mist as needs be.

Compost (which you'll need a big pile of anyway) is the most natural way to generate greenhouse heat. It seems duly appropriate to use this energy as a primary resource when designing for this specific indoor/outdoor application.    

Jean-Yves Lepercq wrote:
..The greenhouse is ongoing. It's gonna be 41*28 ft hence around 1150 sqft. The northern side will be a insulated concrete wall. South side will be 5 large double glass windows. Roof and small sides will be made of 32mm polycarbonate. Structure will be made of wood...

..Problem is I need to heat up the baby every night during october to march/april. Winter temperatures here are around freezing point and days are very short. At night, without heating, inside temperature will probably go as far down as outside temperature. Which is totally incompatible with my orchids and all the delicious veggies of my wife...

..- I want a batch box because due to our activity we won't have 2 hours to spend each day to maintain a J tube RMH...

JY

You need to design for the floor adjacent to the south windows and back wall to function as trombe-surfaces, to absorb direct-gain. If your brick containment assemblies can function in this way, use them. Externally, those trees can also serve to create or enhance a desirable microclimate. You might also consider pond and compost-type water-circulating heat exchange designs.

Will you be using WWOOF -associates & laborers?

I'm new to this thread.

I want to build a bunch of hot frames on my back patio, and heat them with a rocket heater. This would also give me a chance to play with a rocket heater outside for a year or so before putting one inside my house.

Basically, the beds will be the "bench" of a classic rocket heater; brick walls with earth infill.

However, I'm wondering how to insulate it. Will the edges of the mass be too hot for foam board type insulation? I'd like to isolate the mass from the slab, and also insulate the sidewalls. How many feet of mass would I need between the pipe and the insulation? Of course, the price of failure outside is smaller then inside; if the whole thing starts off gassing, it will not be in a contained area. Still, I'd like to avoid that if possible.

I've looked into rockwool board, but there are no local suppliers and it is very expensive. Perlite and organic insulations would get sopping wet and loose insulative ability. Anything plastic wrapped gets us back to the melting problems.

Gilbert Fritz wrote:I'm new to this thread.

I want to build a bunch of hot frames on my back patio, and heat them with a rocket heater.

I lived in Denver for 10 years and I consider the rocket mass heater to be a waste of time and energy for this application. Before planning and building gardens in this environment you might find it important to study a manual on xeriscaping just to become familiar with the realities of sudden humidity drops down to around 10%.

Even though it doesn't resemble Scottsdale, Santa Fe or Phoenix, all the same "semi-arid" (read desert) rules apply right up until you begin to get those regular Spring and seasonal Summer rains. As to building a RMH in your yard and extending the use of your living space accordingly, I strongly agree with the principal lifestyle benefits this could bring.

Google: "Dome Greenhouse, Colorado" and you'll gain insight on 'how to' abate the harsh mountain climate, the expensive way. Picture your same Denver lot in Summit County, and one might certainly begin to brood the combination of the RMH add-on for these gorgeous kit-built geodesic contraptions.

"Hot boxes" function first, in proportion to their depth. A 1ft deep box becomes scalding hot in all but the coldest months, while a sloping box that's around 16" deep at the front and a 24-26" at the rear should generate plenty of heat to start just about anything at elevations around 5,000 ft. The ability to remove the entire assembly would enable you to get a big head start on not just portable flats, but perennials and bedding plants such as tomatoes and peppers. A small pair or series of matching boxes with 1/4" tempered glass spanning no more than 2' x 4' is the most acceptable way to go. Snow is heavy, and insulating. You simply brush it off as the sun begins to reappear.

Hoop gardens and high tunnels follow the same rules. Start by building something with 3/4" PVC at just over just 3 feet tall, and use standard (not real transparent, but thick) PVC 'visqueen' and you will quickly see what I mean about heat and depth being principally in play. Your beds of lettuce and spinach would be thriving by now.

     

I have a rocket mass heater in my home and also in my greenhouse.  I also have an outdoor cob oven, and two mini-rocket style burners for cooking in warmer weather.  I find the biggest obstacle to heating my greenhouse with the rocket stove is simply the time and energy required to tend an additional fire in my life.   It's only a 6" system, so the firebox is small, and I split lots of kindling.  With only 13 foot of exhaust pipe horizontal run, it isn't the most efficient, but this is a small greenhouse, with only 6' x 12' growing bed.  The rainwater catchment is also piped inside, and that 55 gallon barrel does help to moderate temps.  The brick floor and cob mass also help when the sun shines.  I've been able to grow lemons and keep tomatoes alive (though unhappily) through winter even though I only light the rocket when temps are 20 or below.  I must confess, though, to having a back-up electric heater, low wattage, that has a thermostat set at about 36, so I can worry less. . . It turns on for a few hours many nights when temps drop into the 20's but I don't light the rocket. The rocket is far more powerful, though, and the wall does stay hot for about one and one-half times as long as I tended fire.  So, if I burn the fire for 4 hours, ending at 8pm, I can still feel the warmth from the wall at 2am....and I assume the wall is still warmer than outside temps, (though cooler than 98.6) until morning, because air temps in the greenhouse are usually 20-35 above outside temps if I've run the rocket, but only 10 above if I haven't.

Thanks for sharing, Laura. Nice greenhouse build. I see you guys appreciate what I mean about extending your living space to encompass the great outdoors. Merry Christmas, and Happy Holidays to all who've happened to tune in!

Hi Tom,

I'm not sure I follow you here. Why wouldn't the rocket heater do well at heating frames due to a dry climate? And yes, I know the climate is strange here; I've ran two unheated PVC hoop houses and many cold frames. But they don't do well at starting tomato plants, etc. Are you suggesting compost heated beds instead?

Interestingly, my unheated hoop houses are useless; when the temperature hits 80 degrees outside in February, the hoop houses hit 100 degrees, but then drop down into the 20s again next week. This ruins most plants.

I have a small frame, heated with an electric wire. But I'd rather not use them for the number of frames I'd like to build.

I lived in Denver for 10 years and I consider the rocket mass heater to be a waste of time and energy for this application. Before planning and building gardens in this environment you might find it important to study a manual on xeriscaping just to become familiar with the realities of sudden humidity drops down to around 10%.

Even though it doesn't resemble Scottsdale, Santa Fe or Phoenix, all the same "semi-arid" (read desert) rules apply right up until you begin to get those regular Spring and seasonal Summer rains. As to building a RMH in your yard and extending the use of your living space accordingly, I strongly agree with the principal lifestyle benefits this could bring.

Google: "Dome Greenhouse, Colorado" and you'll gain insight on 'how to' abate the harsh mountain climate, the expensive way. Picture your same Denver lot in Summit County, and one might certainly begin to brood the combination of the RMH add-on for these gorgeous kit-built geodesic contraptions.

"Hot boxes" function first, in proportion to their depth. A 1ft deep box becomes scalding hot in all but the coldest months, while a sloping box that's around 16" deep at the front and a 24-26" at the rear should generate plenty of heat to start just about anything at elevations around 5,000 ft. The ability to remove the entire assembly would enable you to get a big head start on not just portable flats, but perennials and bedding plants such as tomatoes and peppers. A small pair or series of matching boxes with 1/4" tempered glass spanning no more than 2' x 4' is the most acceptable way to go. Snow is heavy, and insulating. You simply brush it off as the sun begins to reappear.

Hoop gardens and high tunnels follow the same rules. Start by building something with 3/4" PVC at just over just 3 feet tall, and use standard (not real transparent, but thick) PVC 'visqueen' and you will quickly see what I mean about heat and depth being principally in play. Your beds of lettuce and spinach would be thriving by now.

Was there ever a DVD set produced or part of the kickstarter collection that was specifically directed at greenhouse use?  An acquaintance runs a sizable greenhouse/garden market commercial operation nearby and uses wood to heat his greenhouses.  I'm sure he does not use RMHs to do this and hope soon to see how his greenhouse heating systems are designed and organized.  They must be pretty big burn chambers because he was mentioning using 1.5 ft diameter unsplit chunks of oak to ensure that they will burn through the night.  Was just thinking that if he were receptive to trying a new greenhouse built around the RMH concept, I would gift him a set of the DVDs purchased from Paul,......but was hoping there would be something specific to integration of RMH technology with a greenhouse that he could sit and watch.  Thanks.

Enjoying and appreciating this thread. We're considering a lean-to greenhouse up against the south wall of our barn/workshop, with the RMH inside the barn itself and near the wall where the greenhouse is on the other side.  Then, thermal mass somehow coming from the RMH into parts of the greenhouse on the other side of the wall.

Holy moly there is a LOT of items to read thru... I am guessing keeping on the most recent end will be the best option?
In the beginning there was mention of a certain book being the only thing in print, that was 5 years ago... is that still true or is there something more recent and what is the best for my area in Idaho?

Thanks!

As part of a kickstarter (maybe the rocket oven one) I got plans for "Greenhouse 8" Rocket Mass Heater Plans".  Not sure how to buy it directly but it's somewhere here on Permies.  That's probably a good place to start your search.

Hi Dina;  Possibly the book you are referring to is the original Rocket mass heater book by Ianto Evans  & Linda Jackson. For years this was the RMH book of choice. Its still a good choice for backround.
There is now a newer option called the RMH Builders guide by Ernie & Erica Wisner.  This book is now the RMH go to book for accomplished builders and first timers.
My green house in northern montana has an 8" J tube and uses less than 5 cords all winter to keep it 40-70 all day and all night with NO FIRE from 10 pm -6 am .... pretty neat huh.
If you are just learning about RMH's be prepared to get the bug ... you'll be up half the night reading ... and soon .... you'll want to become a rocket scientist yourself!
ENJOY !