Heating With Compost

David Trammel's picture

Anyone have experience with using the heat byproduct of the compost process to heat water?

I've read of it being used to heat green houses in the Winter but not this specific method. BTW that's one huge pile of compost.

That is indeed a huge pile of compost!

Ken's picture

I have 4 horses on my small acreage. They eat 25-40 lbs of hay per day each (varies with the temperature, quality of hay, etc.) With the water weight, that winds up being 200 lbs of manure per day more or less. So I have some daily real-world experience with compost! (btw - whatever I did in a previous life that I have to spend 20 years shoveling the Augean stables this time around, I hope I don't do again) In my experience with horse manure compost (little or no bedding) I find that it only generates a significant amount of heat under very specific conditions. Air and soil temperatures have to be fairly warm, moisture content has to be in the right range, basically spring time weather. It will break down over time, especially with plenty of worms but generates very modest amounts of heat. With a tarp over the pile, the garter snakes love the warmth but as far as utilizing it as a heat source? Seems like WAY too much work for the calories. Fresh manure in hot beds in a greenhouse might be worth exploring, especially since the end result is already where you want to use it.

The French guy that does the giant piles of woodchips with coils of pipe in the stack might be on to something but that's a far different scale and set up than animal manure. The old classic 'put the weaner pigs on the manure pile' (think Wilbur in 'Charlotte's Web') might be the best use of the modest amounts of heat generated by livestock manure piles. The other aspect is that fast composting, which generates heat, reduces the nitrogen in the compost significantly. So you can't really have your heat AND have your good fertilizer too. If you're just looking to improve soil tilth rather than add nitrogen, the woodchip composting idea might be worth trying. Maybe run a cold water line through the pile to preheat it before it hits your water heating system or just to warm it for irrigation. I'm a big fan of irrigating with warm water; seedlings in particular can be shocked by cold water irrigation.