rocket mass heater for greenhouse

After seeing how efficient the RMH is, I would like to pick your brains on creating one for a greenhouse.  We put up a 30'x120' Harnois ovaltech3 with double walled poly. I'm currently digging trenches to put in 1/2" pex piping 18" deep with 2' spacing and was planning on using a propane water heater or bio-furnace to heat the water, but no I'm wondering if RMH would be better. The greenhouse will be divided into 2 areas, one 85' section for the beds and 35' for starts. The greenhouse has a propane furnace but would be expensive to run exclusively, and don't plan to run it in the very cold month and hoping the RMH will keep things alive after the 10hr day passes.  

I am thinking of placing it outside the greenhouse in a building with our well that will be about 15' away from of the greenhouse and piping the hot water in.  Another option might be to put it inside the greenhouse where the two areas meet, which would be about 4'x28'. Thanks

Welcome to Permies!

I am only an armchair rocket stove scientist, and my greenhouse remains unfinished,  but the thing that stands out is the buried PEX lines.
Heating in  ground beds that are not decoupled from the surrounding earth is probably a losing battle.
A perimeter barrier of insulation is often recommended in these situations, either layed out horizontally or burried vertically.

Thanks, can't believe I didn't find my way here sooner.

I agree I should of put in some foam board along the outside and I just might have to make it project for the fall. The walls going into the ground does have polycarbonate panels going down 2' on the sides but not much r-value at 1.5 and the bottom of the end walls is rubber rodent barrier going into ground.  We had planned to do an Ground to Air Heat Transfer system but we didn't have a 10' drop for drainage, so the contractor recommended the pex as an alternative to use with a propane hot water tank or an outdoor wood furnace. But hearing about the RMH and the amount of wood it uses, seems like something I should explore.

I like it, it sounds like an iterative process.
I definitely would want the rocket inside some structure.
The greenhouse space is precious.
The well house, is there room for any firewood storage in there?

Well I explored, using that "search" and it looks like inside the greenhouse would be best all around.  Would the exhaust need to be piped outside or could i keep it inside to take advantage of the co2?

Your right it is precious but there might be space where it transitions from the growing area and starts area. Possibly 3-4' and about 25' giving about a 4' passage to move through.  The governments greenhouse specialist would be looking at me sideways if I mentioned putting something like this in there.  All about the sqf$ but I'm hoping the RMH would save us the money on propane that it will be worthwhile.

That sounds like plenty of room.
A heat exchange coil immersed in an open top boiler of water is considered a safe option for hydronic heating.

I'm preoccupied with using hydronic heating to move heat from outside into a building, because a homebuilt stove inside my house isn't an option.
I like the idea of using tanks from waterheaters as the boiler vessel.
They come with threaded outlets and they are fire tested.

Kris, welcome to the forum!

Have you seen these threads that you or others might find interesting:

https://permies.com/t/60923/Wet-Tolerant-Rocket-Mass-Heater

https://permies.com/t/151152/Suggestions-sustainable-inexpensive-Greenhouse-heating

https://permies.com/t/94457/Starting-greenhouse-RMH

William Bronson wrote: That sounds like plenty of room.
A heat exchange coil immersed in an open top boiler of water is considered a safe option for hydronic heating.

I'm preoccupied with using hydronic heating to move heat from outside into a building, because a homebuilt stove inside my house isn't an option.
I like the idea of using tanks from waterheaters as the boiler vessel.
They come with threaded outlets and they are fire tested.

Do you have a thread going on it? I thought I was reading it yesterday but now I can't find it.

Anne Miller wrote:Kris, welcome to the forum!

Have you seen these threads that you or others might find interesting:

https://permies.com/t/60923/Wet-Tolerant-Rocket-Mass-Heater

https://permies.com/t/151152/Suggestions-sustainable-inexpensive-Greenhouse-heating

https://permies.com/t/94457/Starting-greenhouse-RMH

Nice, thank you. I will dive in.

Uncle Mud's Webinar on Heating a Greenhouse with an RMH is schedule for Jan 14.

Jeff Bosch wrote:Uncle Mud's Webinar on Heating a Greenhouse with an RMH is schedule for Jan 14.

Thanks for sharing that. Now I have possibly that and r-future to look forward to this month.

"How con-VEEN-ient!" -Dana Carvey
(Sorry couldn’t resist)
Thank you

Anne Miller wrote:Kris, welcome to the forum!

Have you seen these threads that you or others might find interesting:

https://permies.com/t/60923/Wet-Tolerant-Rocket-Mass-Heater

https://permies.com/t/151152/Suggestions-sustainable-inexpensive-Greenhouse-heating

https://permies.com/t/94457/Starting-greenhouse-RMH

Wow, that was quite the adventure you sent me on. That led to all kinds of great information. I now want to grow more weeds on my farm and the epic rmh build by Midwest permaculture with comments was very helpful. Thank you

Kris, the rocket needs to be exhausted outside the greenhouse so you don't kill the plants and the people inside. If you missed our rocket greenhouse presentation you can find a video of it here https://permies.com/w/208519f51/Heating-Greenhouses-Rocket-Mass-Heaters
Insulated earth is the place to store heat in a greenhouse.