Craig Mason

Hey all, I apologize that I have not been able to respond to the advice given. I have been out sick for a while.

Alright! I am reluctant to do it but I will keep the J-tube inside the greenhouse. Aside from the possibility of backing up smoke it the case of a failure or reversal, I noticed last year that when the stove was really fired up, I would get a case of 'cold shoulder'. When rocketing along at full blast, the stove produces a ton of draft coming from every crack in the poly-tunnel greenhouse. Though we've addressed the larger cracks and flaws causing the draft, it won't be possible to plug all of them.

So... I will cut a hole in the sidewall of the greenhouse and place a vent tube as near as possible to the intake. If that doesn't do the job, I'll science it and use a small radiator to heat the water which will run off of the bell and attempt to pre-heat the air coming in. I can adjust the size of the thermal exchange so that as long as it's running, the cold air and the hot water will regulate one another...in theory.

I'll address the reversal and failure potential with a thermal monitoring system on the burn chamber which will shut it down if the fire goes out. Most of that is already done.

Next question: I see in Ianto's book that the riser should be approximately twice the height of the tunnel. But I've also seen others suggest that the stove becomes more "rockety" by increasing the height of the riser. Is there any harm in increasing the height of the riser by 10 or 20% to help things along? The riser is the primary "engine" so it would seem to make sense that it could be lengthened a little without adversely effecting the whole system.

OK, sorry I couldn't get time to address everyone's input individually but I want you all to know that I have read your comments and will take them to heart...And thank you for the help.

Thanks Thomas!

I was able to read your post describing the joys of rebuilding an RMH in the middle of winter prior to pressing the "post" button. I'm into the science of things but I'm not a scientist so I am always hoping there's someone who can translate into plain English. I was able to glean that the longer tunnel did not work as others had mentioned but I'm not understanding the "why". Are the gasses cooling too much before starting up the riser?

I'm designing my RMH as dual fuel. I have an oil burner which will drop down in place of the wood when needed. Preheating will be done with propane in the same apparatus so starting with the oil will produce no soot or emissions. My first redesign was planned to use oil only and so I eliminated the J tube all together. The J tube's only purpose seems to be to make sticks burn very efficiently and then turn their upside down fire into a right side up fire. Jacob Klingel seems to have built a successful RMH while eliminating the J tube altogether.

My last build was an experiment gone awry and once started, could not be undone. I will have a proper clean-out system on this one and my mass will be cob, not a bed of rock. The length of my bench pipe, because it will be straight, will have a small steel cable residing permanently so that it can be quickly cleaned by pulling a chimney brush through and back. It will also have an Arduino board built into it to automatically damp it and shut it down if there are failures. I might even be able to make it send me a text.

By "transition area" are you referring to where the cooling gases come down from the bell and then into the horizontal pipes? I was not able to figure out a good way to make that any larger so I just used about 1/3 of a 55 gallon drum. Any ideas to give this a greater surface area?

This experiment involved a 46X20, double layer, insuflated hoop style greenhouse.

If you care to help but would like to skip the background info, please see the question underlined and in bold.

The RMH experiment proved successful...So much so that somewhere around December, it quit working.

Though that sounds like a failure, I did not heed the warnings of those who suggested against the use of a steel tube liner in the riser. The liner was meant to hold the insulating perlite mixture in place between itself and the outer tube which was a triple wall insulated stove pipe. Thought the insulation value was great in producing the thermal gradient action the RMH is known for, the weak link was the inner liner. This spring, I finally had a chance to assess the failure. After removing the bell, I was perplexed at what I saw because it had little resemblance to what I'd constructed the previous fall. After digging through the ashes and lots of lose perlite clay mixture, I lugged a molten blob of what used to be the inner liner out of the rubble. It had melted and then slumped to the bottom, releasing all of the insulating material that the liner was supposed to be holding back. Simultaneously, it stopped all airflow to the RMH creating a catastrophic failure. We awoke to a smokey, stinky, ruined garden. But hey, we made it to December at an elevation of 4700 feet in central Oregon, under about 4 feet of snow, so by any standard, we successfully extended our growing season.

This year, having been preoccupied with a new job, family health issues and the various other "emergencies" that any other homesteader might understand, I am now on a fast track to rebuild from the ground up. I'm hoping for success on the first attempt as I likely won't have time for a second attempt: This year's August feels a whole lot like November, so it should be fairly clear what's ahead.

For this build, I will be placing the short end of the J-tube on the outside of the greenhouse for a few reasons: If it should ever fail or reverse in the middle of the night, it will not be a smokey mess; I also noticed last year that the hotter I would get the system, the colder the periphery became as cold air would slip into the cracks to displace the escaping gases; lastly, feeding the stove the coldest possible air will hopefully increase the density of the air for combustion, like dropping a half a pound of dry-ice in your hot-rod's air-intake before a big race.

So, that's the reason why. And here is the question: What is the longest burn tunnel I can get away with? With the J-tube on the outside of the greenhouse and the bell on the inside, I need to provide ample distance between the two in order to protect the greenhouse framing and the plastic from the high heat of the RMH; granted, I will be using some form of backing material but nonetheless, all of these things will be in close proximity and not necessarily "compatible".

Other delights:
The RMH will be placed to the right of the greenhouse door (photo) and will run the full length of the greenhouse (46 feet) which will help keep that side clear of snow, also clearing the way for low elevation sunlight to penetrate the garden. Given the length of the "bench" (46 feet), does anyone have feedback on the rise? My thought is that in order to have enough left over heat to make the chimney do it's job, I should increase my rise angle. I was thinking perhaps 1/2" per foot of run... does it matter? I know that low and slow is the best practice but even at 1/2" per foot is almost 2 feet of rise... that seems like a lot.

I would also like to know if anyone reading this rambling has any knowledge of constructing a riser from refractory cement? $40 for six little firebricks doesn't make a great deal of sense, economically. Similar to my forge design, I would pour refractory cement into a form between two tubes and then encase it in ceramic wool.  I would use a cardboard inner liner which would then be burned out. My forge is very heavy but stands up to temps of about 2000 degrees. More perlite would also be added to the cement for insulative value.

Thank you for any replies and for any help. Hoping to be able to add some CAD drawings this week.

Jacob, I should be so honored to have my post "hijacked" for a great cause. And there are few causes greater than a winter- worthy greenhouse.

Thanks Jacob! I’ll have a look.

Jacob,
Does your pipe run through the dirt or through the cinder blocks? Is there anything special about the stratification build?

Thank you, Jacob for the pictures and info. Sorry for the late reply.

If I could do my greenhouse over again, I'd cut the hoophouse in half, down the middle, then insulate the north side and place a heat collector there also. I like your idea and it's occurring to me also that this is way too much volume to easily affect temperature.

Our nightly temperatures have been about 10 or 12 degrees. The greenhouse Temps have been between 40 and 50 degrees in the morning. I have a backup propane burner on a thermostat which would easily burn through a 5 gallon propane tank in just a few hours and it has lasted for a whole week. That tells me that we're getting close to our goal with the RMH. With my hopper, I'm able to stack sufficient fuel for about 3 hours of burn time. I estimate that the fuel and coals probably burn until about 3am.

I've decided that if I'm having these results with a 5" system and an inefficient mass, I should be able to bridge the gap with an 8" system and some proper cob. I'm going to go ahead with a bigger system.

Even in the 20s, with full sun, we are able to reach 100 degrees in the greenhouse, requiring ventilation. With a bigger system, I'm hoping to only need to burn at nighttime and perhaps part of the day in the dead of winter.  

'Keep ya posted.

Hi Phil,

Thanks for your response.

Well, Mangoes would be nice… We have a couple of dwarf lemon trees we’d love to keep in bloom but that may be a little ambitious for our conditions. We’re about 90 minutes from Bend and about 1200 feet higher in elevation.

Yes, perlite mixed with fireclay. In my test burn (in the pictures), I was not able to get the riser even a little warm to touch. I am confident that it is well insulated.

I have not relished the idea of starting over but if that’s what I need to do, I think I have proven to myself that this is feasible.

Do you think I can mix the existing rock into my cob? The rock seems to hold the heat nicely but it has enough air-space that it doesn’t seem to give it up. If I rake back a couple of inches of rock, it exudes heat. Is it expected that it should take a few days of heating for the mass to come up to temperature?

Thanks again,
Craig

Hi Everyone,

Winter has pretty much arrived. We’re at about 4800 feet in the mountains of central oregon and I have some urgent questions.

I’ve read a few books by Ernie and Erica, Mr. Wheaton and a few others. I think I have a fair understanding of the RMH but I’m willing to learn as much as I can and I appreciate any help.

I have a 6” system in a 45x20 insufflated double layer hoop-house . I think it is “rockety” enough for it’s size but I’m a little concerned that I may have an inferior system for the job. I built what I could afford… I managed to secure a bunch of 6” stove pipe for almost nothing. I started with a fire-box and if I remember correctly, a 15” tunnel. I have cut about 1/3 of a 55 gal drum to act as a base for the bell. This allowed me to built a fairly long riser which seems to accelerate gases upward quite nicely. The riser is an 8” triple-wall stainless pipe over a 6” steel pipe with refractory clay packed between the two. Because I am using a 6” system in a 55 gal drum, I estimated that I had a little room to spare for the added pipe size and insulation. At the base, I have 18 feet of  pipe on a slight upslope which makes four 90 deg. turns before exiting through a 14 foot chimney.

Once the top of the drum hits about 350-400 degrees, smoke is no longer seen, only steam. max temperature on the top of the drum is about 650 while the chimney gets to be about 110-120 degrees.

My intention was to build a hopper above the firebox so that I could let it burn for longer periods without having to feed it so often but the lower box edge allowed smoke to escape the firebox at lower temperatures during startup. I then rebuilt the firebox with roughly a four foot square tube down the middle… and yes, I know this is unconventional and probably not recommended but it works great to contain longer pieces of wood for longer burn times well into the night and smoke is never seen. It is difficult to get started but has contributed to the rockety-ness by providing an accelerator tube for the air. The heavy gauge tube stays cool to the touch. I have a 5” variable-speed computer fan which snaps over the top of the tube which I use to get a hot base of coals before feeding longer pieces into the stove.

I did not want to build a cob mass for the system until I could prove that works. I have built this system in an existing grow bed and filled the bed with 1”-minus rock.

Questions:
•I have fired the stove for three days during the waking hours, though not continuously. I notice the rock is warmer each day, presently 90-110 degrees. How long should I expect it to take for the stove to effect the temperature of the thermal mass? Days, hours…? Last AM temperature reading outside was 38 deg while the greenhouse was 50 deg.

•Based on the numbers provided, do you think this stove is sufficient for a greenhouse of this size? The family says I should tear it out and build a bigger one but I think 500 deg sustained should be enough to do the job and it’s efficiency may be improved by a better built mass.

Thank you again for any help. It’s greatly appreciated and you might just save a tomato’s life.

Pictures: Greenhouse in winter without heat; anatomy of the stove without the bell and mass; semi-finished system with a yard of rock and 500 lbs of steel on top of the stove (not touching the surface of the barrel).