Manure Compost as Passive Greenhouse Heating

Here is a photo of a big steaming pile of s**t.  Actually, nice fresh stinky horse manure.  I'm going to put it to good use.

In trying to figure out how to keep our greenhouse heating costs down, I thought I'd investigate a couple of ways of increasing the night time temps of the space.  Previously, I blogged about how our greenhouse benches (aka tables) sit on barrels filled with water.  The idea was that the barrels would absorb heat from the sun during the day and exude it at night.

 

Then I thought of a way to add a little extra something something.  I looked around the farm and realized that this old orchard box would fit perfectly underneath a bench and inside of the barrels.  Hmmmm, let's get seven more of these boxes.  John, or master composter and our worm-keeper, sprang into action and arranged to bring me enough bins.

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Filling the large boxes with fresh manure would start the decomposition process, and heat up.  The mass will give off much-needed warmth for the time it takes to decompose.  Since I'm only heating my greenhouse for a couple of months while I propagate and grow on tomato seedlings, I figure by the time the masses cool off, I won't need the supplemental heat anymore.  At least that's this season's experiment.

Daniel, my excellent volunteer, has been endlessly patient positioning these giant bins in place and moving the manure into them.

We needed as much compression of the manure into the bins as we could get, so we put our newest volunteer, Sarah, to work stomping on it.  I'm glad she took me seriously when I told her to show up with rubber boots.

Once completely topped off with manure, we repositioned the bench tops.  Now they're ready to accept our young plants, help warm up the greenhouse, and definitely exude that fragrant "je ne sais quoi" that will keep people wrinkling their noses a bit upon entering.

Comments

I am in the process of building my greenhouse and currently making do with a hoop house at this point. I was planning on doing the black barrel method of adding some heat for the couple of cold months that we have but I love the idea of using horse manure also! In researching this I see comments about the fresh manure adding too much ammonia to the air and killing the plants...have you had a problem with that?

this gives new meaning to bottom heat. Awesome idea! would love to know how that worked out.

What a cool idea. I'd be interested in the results of your experiment. How large is your green house? I'm looking to do something similar in my small greenhouses this fall in Texas.

It's also OK to just wrap the barrels in black plastic or landscape fabric; this helps draw the warmth without having to paint them. From the looks of your setup, you could probably wrap the whole bed, which might even speed up the composting.

Hi - Just starting a compost heap in my small passive solar greenhouse - I read that compost inside a greenhouse might release too much nitrogen, which could kill plants. Have you experienced any problems with nutrient imbalances since installing the heaps?

Yep, Jeffrey, you're right. I just couldn't find any black barrels, and when I needed to install the barrels, I couldn't spare the time to spray paint them black. Such is the life of a farmer. We make do.

Just thought id let you know your barrels should be black instead of white. During the day when the sun is out the black absorbs the heat and then releases it throughout the night.

In days of old I built my compost heating piles using oak pallet for the sides. This gave all the aeration needed. This was in the Fairbanks area. So it was plenty cold.

I'm just looking in to manure as a source of domestic heating and was reading a guide to composting horse manure that talks about aerating the pile with PVC pipe with holes drilled in. Heat in my 2 horse pile has been measured at 45 degrees C. I just have to experiment with how to get it out and how much I can take before decompostion slows down.

I wrote an article on heating your greenhouse with compost where the "bins" are on rails (train car type) so that you are constantlt feeding in a new "car" of material from one end while taking out a "car" full of finished material from the other end.My other idea is to keep the north wall heavily insulated and have a large insulated cover that is reflective underneath such that during the day when it is up, it reflects additional light down into house (in winter when needed), and then lowers at night to provide a blanket.

In the book, "Solviva," Anna Edey describes how she heated her greenhouse on Martha's Vineyard with manure from her chickens and rabbits.The book is inspirational,as is she.

Have you checked out a product called O2compost? (No I'm not an employee - my mother purchased a small 3-bin system!) As their materials say, "O2Compost utilizes a method of composting referred to as Aerated Static Pile Composting. Using an electric blower, we induce airflow through the pile to maintain aerobic conditions at all times." The system produces EXCELLENT compost and cuts down on odors, although you get LOTS of heat.

Neat idea, but I thought hot composting also requires oxygen for the thermophilic bacteria to really be active. By compressing the pile instead of fluffing it up, you cut off oxygen and end up with a cold pile.

Maybe you can confirm this with a Master Composter.

I haven't tried this, but I wonder if your water barrels would absorb and radiate much more heat if you painted them black?

Cynthia- good work! I actually got a SARE research grant about 8 years back to look at heating hoophouses with big steaming piles of compost. Not only did the compost windrows provide heat, but they also upped the CO2 levels in the houses, which also boosts production. The key, as you probably know, is to keep the temperature up in the compost, which requires continuous additions of nitrogen sources and moisture. Perhaps you and your interns can just pee on the piles everyday, he, he...

I'd like to point out that in addition to heating the greenhouse, the aerobic decomposition of the manure creates a CO2-rich environment, which should be beneficial for your little sprouts.