Heating with compost
A few weeks ago I got my compost heater ready. It’s been on the way for years, ever since I first learned about Jean Pain and his projects. I’m pretty interested in low tech off-grid solutions in general and I’ve been having this as my focus as I’ve been setting up my little dwelling. There’s a lot of clay here. Clay on the walls, around the windows, clay floor with floor heating and last year I built a rocket stove mass heater out of clay. I made it with a coil that’s heating water for the buffer tank, which then in turn sends heat into to floor. This way there’s a lot of mass to store excess heat in. The rocket stove is not any atomic reactor, but it gives off a nice amount of heat with pretty low input of firewood. And especially now, when the compost heater is running and providing a good basic temperature in the tank. So, the compost heater.
It’s basically a box, 2,5m deep, 2,8m wide and 2m high. Looked like this:
This was filled with a mix of wood chips and horse manure. The chips I got delivered a couple of months ago and were pretty dry after the hot and dry summer here, and needed to be watered a lot. The mix was about 10-20% horse manure and then the ret wood chips. The first layer is about 50 cm and then the first layer of coil was put in. I used a roll of floor heating pipe (120m long, ø20mm) and about half of it in the first layer.
Then I put in a drain pipe to provide oxygen into the middle, followed by another layer of chips, approx 70cm. And the second layer of coil and more chips on top. There’s about 13m3 of material in total.
The pipe goes through the wall and is connected to the buffer tank. Inside the heap, there’s a sensor that measures the temperature. When it reaches 45 degrees, the circulation pump starts to pump the liquid (glykol) around and feed the buffer tank. When it goes down to 35 degrees it stops again.
The composting process started pretty fast and the temperature was raising up to 45 degrees within a few days, and has been going steadily since then. Now, ca. 3 weeks into the process it’s still going well and has been keeping a temperature between 47-52 degrees.
At the moment it’s still very mild outside, ca 15 degrees in the days and 7-10 degrees in the nights, so it’s pretty easy to keep the house warm just with burning the stove once a day and with the compost. I’m very interested in seeing how the setup will perform over time and if it can keep generating heat when it gets colder.