Rocket Mass Heater for a Greenhouse

Satamax, would a 7' long bell be better than three lengths of stovepipe back and forth?  

What do i need to do: how to seal the bottom of it, do I insulate under, how far down should the entry and exit holes be for a 6" pipe, do they fit flush or stick in a ways...?

And would I just cover it with concrete to make the mass? I'm in an urban area.  

Thanks!

Satamax, I appreciate your help!  Sorry for the lag here, but had a death in the family.  Now it is time to return to living...   Besides, it is going to be in freezing temps end of the week, and I don't want to kill all the tomato plants..

Can you tell me which would be better: a barrel "bell" system after the manifold, or three 7' lengths of 6" pipe?  Would I use a pair of fullsize 55gal drums, or the smaller 30gal sized barrels?

Would a 6" pipe going from the manifold into the bell barrel work good or does it need to be bigger?  I'm assuming that I should use a pair of whole barrels instead of cutting them in half (how would i seal the "floor" then)?   Would i cut the entire ends out between the two barrels, or make a bottom exit from one to the other?  

Then the 6" pipe exiting the end of the bell barrels should be located low on the end to force the hot air to expand inside the bells, right? Is there any magic distance for inlet or outlet?  

Finally, why couldn't I just mix up quikrete to form the mass around the barrels?

Thanks for your help!!

Like this?

So, your hands are not dirty yet?

So, with three barrels, one above teh riser and two in the bench. You are over maximum ISA for a 6 incher with a bell. IIRC, generally admitted safe ISA, for a 6 inch J 4m² or 40 something sqft.

Here you're about 5.58, or a bit less. But i don't know what to retract from the ISA, for the bottom of the bell. As there is no bottom per se. What i would do in theis case, is to make a bypass in the bell,  to warm up the chimney, just in case it proves hard to start.

Destiny Hagest wrote:Ernie and Erica actually have some greenhouse-specific rocket mass heater plans. I've never built one myself, but apparently this kind of thing can get tricky because of the heat and
damp and roots and stuff all getting mixed together.

Sounds like you already have a plan in mind, but they do have these plans super cheap right now as part of this digital bundle: EEE Package: Greenhouse 8" Heater Plans (3 damp-tolerants heaters)

Hi Stephanie,

Just wanted to give you a heads up that this link isn't working.  

Regards, Scott

That link was to scubbly, which is no longer in operation.

The plans are now available here on permies - you can even pay in pie!

Greenhouse 8" Rocket Mass Heater Plans

Hi Satamax.  Ok, you lost me...  Are you saying that I have too much area with that many barrels?  What if I delete one from the bench: won't that just reduce the heat I can get out of the system?  

Or is the problem just the draft?  How would I create a bypass?  My exhaust goes out the side wall then vertical outside. I thought this would help with draft since the chimney (flue pipe) walls would always be colder than the air inside the greenhouse...?

What do I need to do to make this system work?  It's coooold in the greenhouse!   Thanks!

You're on the verge of having too much.

One barrel is 1.86 m2 you need optimally 4m2 three barrels make it 5.58. m2. But normally you don't count the bottom of the Bell. So i don't know what to retract from your two barrels bell.  

Let say you take off 1/4 of the circumference. You would be at about 4.72 m2 . nearly good, since Forst barrel is not exactly a bell.

So i am saying. Try it,  but make a bypass, so you can start it even in sub optimal conditions.

Hmmm... Bypass surgery...  Like this?

And will concrete mix work for the mass?  Maybe with lots of stones in it?  Thanks!

Yes and yes!

Thank you, Satamax !   I'm heading outside with a hammer and snips to fix the manifold, then build up the new mass bed!  Thanks!

Would it matter if the 6" inlet at A is actually at the bottom of the bell barrel instead of at top?that's where it exits the existing core and manifold, and It seems like it is the exit to the chimney flue being low, that would matter most?

Here"s a view kind of down on the newly modified/opened up manifold.  It is now 4-1/2" across for most of the 12" length.  Kind of a flattened D shaped opening...  I'm hoping that will have sufficient flow for a 6" system?  

So, what would be the CSA of a 4-1/4" x 7" rectangular pipe? Anyone?  The manifold should flow a bit better than that, I would think...

I'm also going to add some concrete to the floor of the first barrel, to smooth the flow of air into the manifold...

The rectangle  pipe should be  29.75 , and the csa of the pipe is 28.27 so you have a smidge more.

Nice plenum now!

Awesome! Thank you for figuring that out for me.  Can anyone tell me how THICK I should make the concrete mass that I'll be pouring around the drums for the bench?  (Since I'm urban I'm using concrete instead of cob).   I was guessing that at the closest points to the drum, I'd probably want it between 1 to 2 inches thick for structural stability? That makes it considerably thicker at the corners...  Is that too much mass, or too little?  Thanks!