For those of you up north: Is it feasible to warm a greenhouse by composting organic matter inside?

I've been curious about this as well.  I wouldn't see why not.  I was thinking of doing something like this by perhaps running some heavy PVC pipe and then piling compost on top, then running air through the pipe to extract the heat from the compost and out into the greenhouse.  I wonder how long the heat would last though?  Would it last through several months of winter?

I've also heard of using painted black plastic barrels filled with water to capture heat and release it.   Another option might include an "earth tube" (essentially geothermal heating), but the up-front costs would be quite high (unless you had access to an excavator).

Not for a sustainable length of time. Depending on the size of the pile and components of the compost mix and the frequency it is turned, the pile will heat up within a few days to between 140 and 160F but cool down to 100F after a cpl weeks. Recommended size for a pile is 3 cu ft minimum. To turn it, you will need that same space. One problem will be the lost greenhouse space due to heating/composting. The other will be the total BTU output by the pile and the and how quickly it cools. Lots of other considerations such as watering the pile and insects. Don't think it will do it by itself (depending on the greenhouse size and desired temperature at night).

Here are my thoughts.

The winter months are much too long and cold to offset the amount of heat that can be put out.

Composting isn't normally that consistant. You get a heat up and then it goes away until you turn it or add more.

Black rain barrels wouldn't have enough solar gain. In january you can have weeks go by with no sunshine.

Geothermal would be a big investment.

Bio-boilers are becoming more and more used by comercial growers.

Natural gas is still one of the cheapest, cleanest ways to heat.

Jean Pain did some amazing stuff with anaerobic composting. http://en.wikipedia.org/wiki/Jean_Pain

A small rocket mass heater might be something to consider for your situation James.

I don't have a greenhouse... this is just where my thoughts go at 2:30am.

Here's a passively heated solar greenhouse.  The space isn't huge and the entire back wall is sacrificed but it supposedly never got below 33F in the winter even with it being -13F outside and being sited in a windy hilltop location.  I imagine it could scale to be longer and perhaps wider and taller.

My assumptions were that the question had more to do with heating the greenhouse up to a temperature that you could actually grow something, not just keep above freezing. I think if all you were after was keeping it above freezing, there are plenty of options that you could look at in conjunction with each other, but I still don't believe a compost pile could do it on its own.

Any smells?

In the new permaculture book by Peter Bane a heating system called "the climate battery" is used in Colorado greenhouse. I don't understand it very well but it pumps air through the soil and somehow the soil warms it. Maybe it is kind of like geothermal but I don't think it is as expensive and I got the impression that it is more simple.

Wouldn't the fumes be toxic? Not sure which gas comes off compost, would think methane, but also pretty sure not safe to fill a greenhouse full of it.

luke

I think this former biochemist in Dittmer, MO is growing figs in two high tunnels, one heated by cooking oil and one by a fan that blows hot air in the day through tubes buried in the ground and then reverses at night.

http://transitionmissouri.ning.com/profiles/blogs/saturdays-farm-tour

There was a fellow in Dungeness, WA who grew tomatoes, etc in a green house in the winter. They typically have a fair amount of sun in the winter. His trick was to have a glass top, but the whole thing was buried about 6' deep in the ground. The ground temp typically was well above freezing, and provided insulation, so it was a simpler proposition to heat the air because of less thermal loss through the sides.

The other question on using compost is this: how much compostable material is available in the dead of winter to keep the pile going? And how much space do you need in the greenhouse to compost enough material to provide sufficient heat?

Youtube has a lot of solar heaters all scavenged parts in some, soda cans, alum. downspouts, etc  looks fairly simple.

Check out this link for making heat from compost. http://onestrawrob.com/?p=1144

Jon,

In Western Washington, the base material of the area is warmer than the average for the United States. I remember reading somewhere on average the base material in this region is around 60 - 65 F. On average the american base is 50 - 55 F. This is why one is able to use geothermal systems for residential housing. The temperatures are a constant measurement while the actual cost of pumping the fluids throughout the systems is fairly cheap, about 1 - 2 dollars a day.