mass heater in the ground for heating a greenhouse

First off this is my first post on this site and I really love all the things Ive read on here in the past. Now its time to become involved and start asking for advice.
We live in Fernie bc and its still snowing right now (May7). Our greenhouse provided well through out the winter but on the below 0F days I would love to have some sort of heat in there. The greenhouse kept above freezing most of the winter from just solar.
Although the greenhouse is 20 feet wide by 32 feet long we don't have much room left to put in a Rocket Mass Stove. I was wondering if a person could build the thermal sink ing the ground and have it heat from the ground up?
is this even something that could be possible?

Any thoughts would be great.

Hi andy; Yes , you can run your pipe in the ground ,but you will need to insulate underneath to keep from trying to heat the ground. Also you will need to place it so that nobody is walking on top of it. We have a greenhouse 12x20 and heat it with a rmh. I removed the dirt from one of the raised beds and used that area as my mass, we now use that bed to put all our starts on, keeping the nice and warm all night long. The babies love it and pop up much sooner than before , and we do not miss using that bed for full time planting.

This is a awesome start. Thanks for the reply. Why is it that we can't walk over the thermal mass. Ideally I would like the mass to run down the walk way in the middle of the greenhouse. If this isn't possible we will need to look at changing a few things for growing configurations.

Andy; The problem with walking on your mass ,is possibly crushing the cob tunnel that your heat is traveling thru. The stove pipe or hvac pipe that you use is not very strong even when new and it is expected to rot away over time leaving a smooth cob tunnel for the heat . If this caves in you will be unable to use your rmh without a total rebuild of the mass.

Andy weir wrote:Ideally I would like the mass to run down the walk way in the middle of the greenhouse.

Why? Wouldn't it be better to be able to grow the tenderest things things right on top of it, as described above?

Hello! Our RMH is in a greenhouse and the exhaust pipe is run underground. It was a very cold winter here in PA but by the sound of it your winter is still going strong. Thomas made a good suggestion about insulating the exhaust pipes from the ground and I would like to expand on that a little further. Imagine the supposed location of your RMH. Now dig out that entire area and make a"sandbox". There are a lot of materials that can be used for insulation, sand is one of them. I only mentioned sandbox so we have a common shape for discussion purposes and not speaking about the thermal properties of different materials. Place your RMH and the exhaust pipes within the "sandbox" and fill it in with what you have available. Preferably something that will store the heat and release it over time. What you will end up with is a nice warm area that will radiate heat over time and the "sandbox" will protect your mass from the cold, damp soil surrounding it. Best of luck!

I wounded if going to a thicker walled exhaust would still transfer heat so that we could still put it down the centre. Half the problem is that we have all our soil and bedding in, and after 3 years of working on the soil my wife would not be happy if we dug it up or even made any changes to our productive planting layout. This leaves us with only few options if we want to heat it, and thats why we want to heat under the walk way.
If this still can't work then I think we will need to expand to gain the room for the stove. Ether way I think its going to be a interesting fall when she do the install

Andy; I would guess that if you used schedule 40 steel pipe it would hold up for a good long while ,but eventually it would still rot out and the cost would also be very high. Imagine having the pipe cave in, in 10 years , without any way to see its condition you would have to dig it up just to see ! The mass on my rmh is apx 15' long x 2.5' wide and 2.5 tall with my core at 90 degree's, that's not that big an area if your greenhouse is 32' long. After your wife experiences having a rmh in her greenhouse she will be so happy, that any changes you make will be forgiven. My wife was not excited at all about tearing up her raised bed and although she won't admit it, didn't really believe that a RMH would work. Now she is a believer ! As I think about this you could possibly use brick to have support walls along side your pipes and a 1/4 " steel plate sitting on the bricks over your pipes to protect from walking... hmm ... might work . where there is a will there is a way!

The Derrick Heater was designed for greenhouses, barns, and other informal situations. Its appearance is deceptive because it just looks like a stack of steel drums. However, inside the drums, you stack your own dense fireclay bricks around the perimeter of the tall stack of drums. These bricks absorb and store the heat from the exhaust of an 8" combustion system. The tall stack of steel drums constitutes a bell (rather than a flue). The bell allows the natural stratification of the gases from the exhaust and the cooler gases fall right out and into the chimney. In this way you are not heating dirt or cob (neither of which are as good at conducting and storing heat as fireclay). The fireclay bricks radiate the stored heat through the steel drum over night when they are well-charged (burning for several hours) during the day.

The Derrick heater can be disassembled and moved out of the way during the summer.

We had to build a bump-out for the Derrick in our greenhouse; we put it on the North side of the greenhouse and insulated the solid walls with mineral wool. Our tomato plants lived through the winter. Yes, I'm in southern Texas, but we did go into the 20's several times this past winter.

A daft idea, you could dig a trench, insulate the bottom, and then make a sort of flue with pavers on the bottom, bricks, or concrete blocks on the sides and again pavers on top, lay a little layer of clay on top for airtigntness (if that's realy needed. And then cover with gravel. That way, you can walk on it, and it's a prety nice mass.

This last idea, making a draft with pavers sounds great. I look forward to having heat for the real cold nights.

Andy weir wrote:This last idea, making a draft with pavers sounds great. I look forward to having heat for the real cold nights.

Andy, still use some thick ones on top, like 2 inch. You could also make it wider than necessary, to increase the contact surface, and make a bell ish implementation.

Hello Andy,

I'm also from Fernie and excited to hear about your greenhouse project.

Where to begin...

There's actually a group forming of RMH enthusiasts in Fernie with various projects planned for this summer. We had a meeting last month at the bakery to get some ideas going - so perhaps we should get together and collaborate. We've talked about hosting a workshop with DirtCraft Natural Builders and if not they already have one scheduled at the Groundswell Community Greenhouse in Windermere early September.

There's a guy in the Hoz who built an RMH in his greenhouse - perhaps we should organize a field trip?

If you're primary concern is providing backup heat for your greenhouse I would highly recommend combining a RMH with storing the excess heat from the summer.
For ideas Google terms such as:
Annualized Geo Solar
SHCS Greenhouse
Climate Battery Greenhouse

Or come and check out the one at my place in Ridgemont. It would be straight forward to trench one in below your existing path

Oh and check out Rob's videos for a stellar example of integration
Bigelow Brook Farms

Talk soon,
Darren (a.k.a. D'S Drywall)

I live in west Fernie and would love to pick your brain. Contact me through email at weride@weiboondocking.com maybe you would like to stop in for a beer or coffee in the greenhouse on a rainy day.

wow I was just looking at how far away some of this advice is coming from and really am shocked. Thanks again to all that have given input.

does this help?