Mass heater (non rocket) in greenhouse

Hi everyone, first post here...

I'm putting in a 12x12 greenhouse and I want to put in some kind of mass heater to keep it warm during the coldest parts of winter. I'm in 8b or 9a hardiness zone.

I see a lot of people creating a rocket mass heater, but that involves barrels or other metal. I would like to create something more akin to a small russian stove in the shape of a bench. So low but with a lot of serpentine heating ducts within the bench.
I only intend to fire it during the coldest times of the year, so probably every two weeks. Otherwise I want it to be a heat mass that absorbs heat from sulinght

I don't see people building this kind of mass heater, is there any reason for this? What other cons are there that would make this a bad idea? Would it make it too hot in the summer months?

Please let me know your feedback, and it's good to be here!

Hi Demian, and welcome. I suspect the main reason a lot of us build the "lowest common denominator" J-tube with steel drum is that it's quick and cheap, and works well for the glasshouse use case. There's certainly no barrier to going uptown on your build if that's what you want. I like mine because it was a simple design and has survived a couple of rebuild operations that were easy to carry out because everything was put together with cob or clay slip. I also like the ability to use the top metal surface as a griddle...when the thin steel of the barrel burned/rusted out, I just put a round piece of 6mm steel plate in its place and it's the perfect tortilla (or naan) cooker.

Demian -

Welcome to Permies!

Igor Kuznetsov has a double bell greenhouse heater design similar to what you are describing:
http://eng.stove.ru/stati/otoplenie_teplits

The link to the build plans in the above article is broken, but I think this is the bond plan, showing several lengths of heated wall, and options for adding a boiler:
http://eng.stove.ru/products/ptik_1
My Russian is too crummy to be absolutely certain that this is the correct plans, but after looking at several, I think this is the one.  For instance, in the article, he mentions the bypass damper in row 17, and the build plans to which I linked do indeed show a blast gate damper in row 17.  If I get some time, I'll try to OCR the image to Cyrillic text and churn it through an online translator.  But, we're in the midst of selling my dad's house, so don't hold your breath!  If you want to take a crack at this, be my guest.

Ernie and Erica Wisner also published plans for a greenhouse rocket style heater, discussed and available for purchase here:
https://permies.com/t/64464/Greenhouse-Rocket-Mass-Heater-Plans

There is a YouTube video on Paul's channel showing a variation of this, featuring Ernie himself:

The bench could very easily be a bell style, rather than the serpentine stove pipe.  Peter Van den Berg (AKA "Peter Berg"), Matt Walker (Walker stoves) and others have successfully demonstrated bell benches.

Again, welcome, and we're happy to have you here.

Kevin

Demian -

As a follow-on, here's a photo from the 2012 MHA Wild Acres meeting when Lars Helbro (and others) built his Gymse design, with a brick heated bench (and an experimental condensing exhaust, but never mind that part - that's why the bench is so long).

Depending on what materials you have available or for which you have the requisite tools and skills to process and lay, you might build a bell bench differently.

Note that both the heater and bench shown are single wall (as is the Kuznetsov design), and would not meet US residential codes because of that.  However, depending on your jurisdiction, codes probably don't apply for a green house.  Again, depending on your jurisdiction, a lime plaster on the exterior may pass code, since cracks are readily visible and can be repaired to return the masonry heater to a smoke-tight condition.  Lots of European and West Asian thermal mass heaters were plastered, usually with a lime based preparation.  Or, if you have access to a facing material (old stone countertops, roofing slates, salvaged ceramic floor tile, etc), those could be used as the second layer to meet code.  Again, for a green house, this may be a moot point.

Here's the link to the full article:
https://www.mha-net.org/docs/v8n2/wildac12b.htm

Kevin

Hi Demian,

as far as I understand the reason most people here build rockets is they're tried and true, easy to build and reliable. I'm with Phil and Kevin on that one.

If the barrel is the problem, consider a masonry bell, as Kevin pointed out. The core (engine) of the stove can still be a rocket, with the great efficiency that comes with that.

Another problem I see with other mass heaters is the possibility of creosote build up, chimney fires, etc.

Demian -

Here's the mechanical translation (warts and all), via Google Translate, of the OCR'd Cyrillic text from the previously linked plans by Kuznetsov:

"I grant the right to publish this material in any form only to the church of any religion, any country I.V. Kuznetsov.

Stove heating of greenhouses.

What problems do owners of private houses have to solve when growing fruit and vegetable crops in greenhouses? What capabilities should a greenhouse have? Many people dream of extending the operating season of a greenhouse, that is, having a cheap and convenient source of heating. Have hot water for irrigation. In spring and autumn at night, there can be negative temperatures, which leads to the death of plants. Therefore, the greenhouse should accumulate solar heat during the daytime and give it off at night, maintaining a positive temperature in the greenhouse. It is proposed to solve these issues as follows The greenhouse should be placed from east to west with the long side. The eastern, southern and western walls should be made, as usual, of glass. The slope (pitched) of the roof should be made from north to south. The northern side of the greenhouse should be made of solid brick and painted black. It is known that in this case, it accumulates solar energy during the day and releases it at night. A heating stove with a hot water supply (HWS) boiler should be built into the wall.

This stove must have the following functions:
• Heat the greenhouse, and the outer wall should not give off heat and be weather-resistant,
• Prepare hot water, and there should be no cold core in the firebox (coil, the DHW boiler should not be placed in the firebox);
Run on cheap local fuel, which includes firewood (renewable energy);
As a backup, the stove should run on electricity, which will allow people to leave the greenhouse (leave) for a long time,
It should be painted with black fire-resistant paint, for example Kuzbass varnish,
It should be economical and have predominantly lower heating.

These are the properties of the "two-tiered cap" stove, built on the "principle of free gas movement". The stove is made in accordance with Russian standards. With its help, all the issues noted above are resolved. I provide working drawings of the basic model. For the outer shell, solid red brick 250x120x65 mm is adopted. The length of the brick with a seam is conventionally accepted 260 mm, the height of the row with a seam is 70 mm. For the internal lining, refractory brick 250x124x65 mm flat and on edge is used. A layer of ceramic insulating fiber 5-10 mm thick is laid between the outer and inner shells. Electric heating elements 2x1-1.5 kW, with separate protection machines. Heating (raising) the water temperature by 40 C°, 120-180 liters. The stove is fired with the open forward valve (on the 17th row), after the pipe has warmed up, this valve is gradually closed. A canopy for storing firewood can be arranged behind the wall."

There's a discussion of an implementation of such a heater, here:
http://eng.stove.ru/stati/solnechnyiy_vegetariy_iv_kuznetsova


Most of Igor's drawings are fairly self explanatory.  However, this page (see near the bottom) can help decode a few of the non-obvious items:
http://eng.stove.ru/stati/v_pomosch_lyudyam_delayuschim_nashi_pechi
 
For instance, the red grid, shown in layer 17 of the linked plans, appears to be galvanized steel mesh.  The red layers surrounding the fire brick lining of the fire box, and behind the wall bell, appears to be a layer of mineral wool.  The convention he uses to show beveled bricks is also defined.

As Benjamin mentioned, the rocket designs are tried and true.  The J-tube is pretty simple to build.  The aesthetics may be an acquired taste, but for a greenhouse, who cares?  And, the various batch box designs are operated more like (and have a similar aesthetic to) conventional wood stoves - fill it up and let it rip.

As an alternative to a heater, you might also have a look at the Chinese greenhouse designs, which are passive (though not fully passive, as Paul's wofati design, a development of Mike Oehler's underground greenhouse).  These Chinese greenhouses usually have a thermally massive north wall (adobe, earth banked, or even a pit style green house), with movable insulating blankets or curtains to help retain heat at night.  If your climate is mild enough, you may not even need the thermal mass heater (though it would be good insurance, and is a fun project!).  If sufficiently severe, both may be needed.

Kevin

Thanks for the replies all.

My idea is to make a masonry structure that is more of a table than anything else. so about waist height to match the other racks in the greenhouse, and build internal horizontal passages for hot gasses to trap heat before being exhausted.

Most rocket mass heaters go the direction of the barrel riser for instant heat and then a low bench.  But I don't like the idea of having the traditional barrel riser that goes with RMHs, this is mostly based on my biolite campstoves which inevitably start to rust to pieces with continued use, so there's a better chance for gas leakage and such.

A J-tube design was my initial thought, but that design seems like it would require a lot of babysitting to keep the fuel topped up, and it wouldn't be compatible with some of the fuel I want to burn (magnolia leaves). I've thought of using a J-tube for startup to get the draft running, but the main combustion chamber would be either a russian stove style with a grate and blower chamber below it, or a batch box rocket stove, or some combination thereof. This is the unknown territory I want to experiment with.

I've been consuming a lot of content on the russian style heaters, including kuznetzov's plans and builds by expert russian stove makers. I speak just enough russian to get an idea of what they're saying, but I miss at least 50% of what is said. Since posting this I've found that there is a large movement making small versions of these structures in south america, and spanish is a first language for me.

My issue with most of Kusnetzov's designs, and the chinese style passive walls  is that I've never laid a brick in my life and I live in the seattle area where we can get BIG earthquakes, so I'd rather not have the stucture collapse and take the greenhouse with it if it did. The greenhouse is not a custom design.

Demian Alcazar wrote:Most rocket mass heaters go the direction of the barrel riser for instant heat and then a low bench.  But I don't like the idea of having the traditional barrel riser that goes with RMHs, this is mostly based on my biolite campstoves which inevitably start to rust to pieces with continued use, so there's a better chance for gas leakage and such.

Now that I've had a J-tube RMH in my glasshouse for eight years, I have some perspective on the longevity of the drum. Only the top deteriorated to the point that I cut it out and replaced it with a circular piece of 6mm plate with a fire rope gasket. The cylinder is still in decent shape. I put a coat of linseed oil on the exterior every year or two and this keeps the surface rust to a minimum. The interior is mostly coated with fine soot and ash, and as long as the fire is running the flue gas is creating a neutral to slightly reducing environment, which is why I think that outside of the direct heat zone it's held up really well.

Considering the cost of the barrel (free at the scrap yard) I'm not too bothered about the prospect of its eventual replacement.