Mc Martin

I guess I should elaborate on a few things. The greenhouse will be in zone 8, and our winters are relatively mild, but we average maybe 10 nights per winter below freezing. I’m looking for a good way to keep the greenhouse above 40 degrees F during those cold periods.
I heat my house with a regular masonry heater using stored radiant heat, so this is not entirely foreign to me. My farm is off grid solar (8kw), so electric heat is not an option. I could maybe get by with a propane heater, but I much prefer using scrap wood as fuel rather than fossil fuels.
I definitely want to heat what will become a concrete counter top above the pipes or bell chamber to use as a seedling warmer. I’m hoping especially to grow onions and garlic from seed.  Lots of other things, too, but I’ve never been successful with those.
I attempted to research the bell chamber, but ended up sort of confused. It reminds me of a smoker, which made me think I should make it double as that, but I guess with this unit the completeness of the combustion would not have enough smoke?
A secondary function of the greenhouse will be for processing wool (washing, drying, combing, carding, dyeing, maybe spinning) in the winter months (hence the big sink).  I’m a shepherd and have lots of wool. Last, but not least, since I don’t have a dryer, I can hang clothes to dry even if it’s raining.
So, I’m not shooting for 70 degrees, but rather taking the edge off of cold nights.  I think there will be a good amount of solar thermal gain in the 3 foot tall stone walls and precast countertops and stone floor, and that may be enough, but I think it won’t hurt to have this backup.

Thank you, Gerry.

Bell chamber?  This is new to me. I’ll look around for more info on that.

Continuing the thinking on trying to minimize the footprint ... has anyone ever stacked the pipes vertically?

The attached image shows the rmh moved down in elevation so that the top of the feed tube is level with the finished floor, and the pipes are moving vertically rather than horizontally.

Is this a bad idea?

Thank you so much for that answer.

I’m not sure if I should start a new thread for this question, but I’ve finished drawing up the RMH and find that it eats up so much floor space in the planned greenhouse. I’m wondering if it’s possible to put most of it below grade?  The only thing that troubles me is the idea of water infiltration, and that’s a big can of worms.

Thank you for the clarification. I’m trying to pursue your option 2, using full thickness insulating firebricks without additional insulation. I’m having a really hard time finding the brick at a reasonable price. And, it seems that all of the manufacturers are very far away.
All of the masonry supply companies that I’ve called are saying that their firebrick is “fine for pizza ovens”, so I want to clarify that standard firebrick is not acceptable, correct?
The use of insulating brick is crucial so that the temperature inside the heat riser is much higher than the temperature outside the heat riser (but inside the barrel), right?

Hello and thank you in advance for your help.
I’m trying to design my Rocket Mass Heater for my greenhouse based on the information in the book “The Rocket Mass Heater’s Builder’s Guide”.
In building the heat riser, I’m a little confused about the options for the thickness of the brick and the thickness of the insulation. In the drawing that (I hope) is attached, I’m showing the barrel as glass so you can see the thickness of the brick and the insulation. The bricks are full thickness fire brick (2 3/8”), and the insulation shown is 2” mineral wool. These thicknesses seem to make the space inside the barrel really tight, and that doesn’t seem so good. In the corners, the insulation is almost right up against the barrel.
I’d like to make something that is very long lasting, and, from the wording in the book, it seems like this is an option, but I may be misinterpreting what was said.
It also seemed like they were implying that if you use full thickness firebrick, that maybe the insulation isn’t needed?  (Chapter 4 - Insulation Section).

The sheep I raise, Gulf Coast Sheep, are a landrace breed.  They are descendants of the sheep that the Spanish Explorers brought to this region in the 16th century and abandoned here. They became feral for several centuries and dropped their leg, belly, and head wool to adapt to the heat. Their feet are rock solid (no foot problems). They developed a high resistance to the parasites that are fatal to other breeds on the southeast.  They are sometimes misnamed Gulf Coast Native, but they are not native, but rather a landrace.

They are hardy, excellent foragers, excellent mothers, lamb on pasture, and have wonderful fiber. They are smaller than other breeds, and do not have as many multiple births, so they are not a “production” breed.

Their cousins, the Navajo Churro, were also brought by the Spanish Explorers.