New in ground RMH for my greenhouse

So here's my newest accomplishment!

I made a 6" RMH for my greenhouse which is attached to my house. I'm in North Central Idaho and hoping to be able to grow cool weather veggies and sprout fodder for my livestock over the winter in there. Also, my neighbor gave me a banana tree after I finished the greenhouse this spring and the darn thing is fruiting so I'm trying to keep it alive over the winter.

Since the floor of my greenhouse is gravely rock, I put everything except the upper barrel below ground level and buried it in the gravel of the floor.

I've got 18' of exhaust pipe running through the gravel floor and then 12' of chimney pipe, 4 feet of which is outside the greenhouse.

My first attempt failed due to not using a large enough barrel over the heat riser. I used what I assumed was a 35 gallon barrel but ended up only being a 25 gallon. The smaller barrel almost worked but didn't allow for enough draft and it eventually smoked back.

I followed Ernie and Erica's designs for a 6" RMH but did the "5 min riser" alternative for the heat riser. 8" duct with durawool lining the inside.

Because it was all getting buried in the rock, I only did a  small amount of cob to seal the cracks between the fire bricks and the barrel. Yes, I know I should have burned the paint off the barrel before putting it together but I was in a crunch for time with freezing temps at the end of the week and having to tear it apart and rebuild it.

Works good so far!

I've been running it nightly for about a week now and it is keeping my 12' x 38' greenhouse at a toasty 50 deg overnight with outside temps in the low 30's to upper 20's.

Forgot to mention that it has been doing a great job of decreasing the humidity in the greenhouse as well, which is awesome.

It pretty much steams out the chimney for the entire 2 hours that I've been running it each night.

Because I'm spraying the fodder racks at least twice a day. I was really building up a ton of moisture in the greenhouse.

Hi Penny;
That looks just super!   Good Job!
Did you insulate under your 18' run?
Now that you have a 55 gallon barrel your going to be very happy with your rocket.
Soon you will want to build a brick batchbox for inside your home!

Thanks Thomas !

Batch boxes are very interesting indeed. I have an 8" J tube system in the house for now that I built a couple of years ago. But I would love to have something that I could cook on too.

I'd like to do an oven system next I think and then a water heater.

Probably not until spring though. My house is only 1/2 finished inside and I've promised my family that I'd finish the wiring and close up the walls this winter :b

Hi penny, mind sharing what kind of cold you have to deal with in your location? Do you have any sort of thermal barrier in the ground around the green house? I'm trying something a bit similar...

Hi Coydon,

I'm zone 6b. Winter temps occasionally down into the teens each year.

I have 2 inches of rigid insulation covering the 18 inches of concrete foundation that is above ground. The north side of the greenhouse is attached to our house. The greenhouse is covered by used double paned windows and 6mm double walled polycarbonate greenhouse panels.

Thomas - I forgot to answer your question about insulating under the 18' of exhaust and the answer is no. I was thinking of putting a couple of inches of sand under them for some insulating effect but it says pretty damp in the floor (despite having a buried drain) so I don't know how helpful the sand would be as an insulator if it was damp/wet?

Hey Penny;
If it is performing to your expectations and satisfaction,  then leave a good thing alone.
In the future, if you did have it exposed , maybe some ridged insulation on the bottom with sand and perlite  on top to bed your pipe.
You'll get more heat rising that way.

Until then enjoy what you have!
As I said, it looks great!