DIY Rocket Mass Heater Build Log For Commercial Greenhouse

[Bigelow Brook Farm] has a cool geodesic dome greenhouse that needs to stay warm in the winter. There are a lot of commercial solutions for greenhouse heating, but if you’re the kind of person who research and develops solutions for aquaponics, a greener solution may have more appeal.

A rocket mass heater is a combination of a rocket stove and underfloor heating. A rocket stove works by having such a strong draft created by the heat rising up the chimney that the flames can’t crawl up the fuel and burn in the open air, creating a controlled burn zone. Unfortunately, with just a plain rocket stove a lot of heat is lost to the atmosphere needlessly. You only need enough to create the draft.

The mass part solves this. It runs the exhaust under the floor and through radiators. This passively retains a lot of heat inside the space to be heated. It’s a bit of a trick to balance the system so it puts as much heat into the space as possible without stalling, which can be dangerous due to carbon monoxide, among other things. Once the balance is achieved the user gets a stove that can burn fuel very effectively and best of all passively.

[Bigelow Brook Farms] have been working on their heater for quite some time. We really enjoy their test driven development and iteration. They have really interesting autopsies when a component of the heater fails and needs replacing. Right now they have a commercial sized operation heated by their latest iteration and it’s completely passive, being gravity fed. Video after the break.

33 thoughts on “DIY Rocket Mass Heater Build Log For Commercial Greenhouse

  1. While this is a nice design, the fact that wood-burning heating systems are targets for all sorts of regulatory pressure would make me wary of depending on such a system for a commercial enterprise. In my area not only has wood fired home heating been made illegal to install, but now owners of homes with existing systems may be forced to stop using them. Already the places that made bagel with wood-fired ovens, and pizzerias with the same have been forced to change or close, (and neither product has been the same since IMHO.)

    1. One of the supposed perks of these designs is the very efficient & complete combustion of fuel. As long as the flue is appropriately sized there shouldn’t be much visible smoke once the stove is up to temperature.
      Short of particulate emissions I would think these stoves may pass local emissions controls. It would be interesting to know for sure though.

    2. All wood fires? the gassifiers have lower emissions than the more conventional types. The fire types you are describing there are open fires but with gassifiers the methanol is drawn back through the heat of the fire and used to create more energy and soot burnt in the same manner for the emissions reduction. The epa wanted or did ban most wood fires, but the 20% the ban didn’t cover were all certified gassification units.
      Open fires are bad for your lungs long term too…

    3. Thing is national standards are one thing, local bylaws are another and (at least here) we have had some losing fights because the local authorities don’t want to bother sorting out efficient systems from those that aren’t. I suspect this is more an attempt at political peace than anything else. At any rate, home heating falls under local building codes in most jurisdictions, and while there might be minimum federal technical standards, they don’t override what local governments refuse to issue constrution permits for.

      This is a subject close to my heart as I might well have to permanently block the fireplace in my over a century old home that at best we only use once or twice over the Christmas season as the borough I live in starts to tighten the screws.

        1. Ya, well in our case they were a lot stricter because commercial wood-fueled operations were closed first. You might still get away with something like this in rural areas for awhile yet.

    4. Is this government (what country) handing out oil, gas or electric heating systems and paying any difference in the cost of heating to people whose only source of heat was a wood stove? Or are they expected to somehow come up with the cost on their own?

      1. Full prohibitions, as I wrote above, are consequences of municipal bylaws and no, to the best of my knowledge, there is no compensation. However most of the homes in my neighborhood that heat with wood installed this capacity as auxiliary systems when the price of oil got out of hand and still have the old equipment in place and use it when temperatures fall past the point where their stoves can’t keep up. Federally the laws only set technical standards that must be met, but do not ban wood heat outright.

      2. some places in the us, like kentucky, especially eastern ky, were covering 100% of certified clean wood burning system installs for your home I dont know if they still are. You can get around lots of local building codes and insurance regs by placing your rocket stove in an outside building, and circulating hot water into your home from an outdoor shed or “hobby greenhouse”.

  2. You could scan your local small ad’s and if your lucky find a HS Tarm furnace with back boiler intergrated for $300, and drag it home + have it servicable and easy to clean and not have your household insurance invalidated if that matters to you. Yes they are gassifiers (“rocket”), but they also have a flap in the chimney you can shift to change the furnace from conventional top chimney to bottom exit, which lets you start with no smoke then flip the flap once the chimney is to temperature to draw sufficient for the gassification mode.
    The other caution is you can add heat exchanger mechanisms to the chimney pipe but if you overdo it you don’t have enough draft to reliably extract the CO2 which can fall out the intake instead, which results in dead people if done wrong.
    .My hs tarm unit runs my self laid in slab water underfloor heating (controlled by a ethernet connected board as it goes) + radiators upstairs to heat a 3000sq ft stone house and uses the main concrete slab downstairs as the mass storage element. It does take a wheelbarrow of wood a day though. More when its really cold. And that involves a lot of logisitics moving and storing masses of fuel which requires preparing a year in advance so its dried and seasoned correctly. We use 7 cord of wood on average, if your thinking about doing the same, its not for a urban area. Better than a gym membership though!
    I could hook the tarm up to oil or gas too, but I’ve never bothered while I’m fit and healthy enough to cut/haul wood.

      1. *facepalm*
        All plants are starving right now and this can be seen through microscopic viewing of the stomata on the underside of the leaves. We have 250-350ppm CO2 in normal air we need about 3000ppm…..
        What should be as common knowledge as the sky is blue, has become a question.

          1. Probably because you are not a plant :-)

            But it is common to use additional CO2 in greenhouses as fertilization to increase plant production. Sometimes this goes as far as burning natural gas in summer and getting rid of the heat just to produce CO2.

          2. Greenhouses are sometimes equipped with co2 concentration enhancers, but regulations usually stipulate that the room is airtight towards spaces occupied by humans, can be emergency vented to the outside in any situation that may arise, and has a co/co2 sensor that interfaces with some sort of access control system that locks the doors while the concentration is high….

        1. Plants need both CO2 and light AND O2.
          They need O2 to breathe like most living organisms (all plants and animals) Just when the light is strong enough photosynthesis produces more O2 than the plant consumes.

    1. No, because then more energy would be going into heating up sub-freezing air. It isn’t sucking any heat out, most of the heat is going into the sand and water, very little is being exhausted.

      1. Cold air intakes are a thing in wood burning furnaces and some people swear by them because your not drawing in cold air and having to warm it to replace the heated air that drives the chimney, and others at them because they are supposed to make it hard to get the furnace started properly without the warm air in the house rising and starting off the chimney flue process, but one of the reasons I didn’t go with one is that in certain windy weather conditions the smoke etc can be drawn out the intake instead of the chimney and cause a fire.
        I’ve seen ash puffed out the damper flap in weird windy conditions even without a external intake with potential to cause a vacuum, and there’s enough things to go wrong without adding to them.

  3. It’s interesting to watch the learning curve in the video series – he seems surprised that very thin ferrous sheet metal including stainless burns through after being exposed to very hot combustion over moderate periods of time. I don’t see much evidence of carbon buildup though, which is a good sign.

    1. lol. I have burnt thru titanium rods i used for a grate in my rocket mass heater. I have also had an “arkansas stone” ceramic sharpening rod get a 45 degree bend in it from the heat my stove creates. i am using woodchips for fuel, with no air blower added to it. No metal can withstand the heat created in a rocket stove for very long

  4. The lack of any real sealing of his flue pipe and most of the rest of it worried me a bit, hope he’s got a carbon monoxide alarm.

    Bear in mind if you do this it’s entirely possible to set fire to the ground… if it’s high humus content, like the floor of a greenhouse you’ve been digging peat into for years.

  5. He’s built essentially an underfloor Kachelofen. Burn the wood super hot/clean, extract the heat through a fire-brick serpentine, and radiate out at leisure.

    I’ve wanted one for our house since moving to Germany — they’re common/rustic/cozy here, and a neat example of an old but very efficient tech. Oh, and did I mention heavy and expensive when they’re done right?

  6. I have a book somewhere that shows many Europeans and middle eastern stoves where a fire exhausts under a stone floor providing hours if not days of even heating. I even remember the Romans used such a system for their public baths. Downward or sideways drafting is always been a problem and is always solved by a large pressure difference caused by where the fire is located and how it burns.

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