We found this video at Whole Systems Design, a New England based company who identify, design, and develop human habitats. In their own words from their website : "We design and implement regenerative food, fuel, and shelter systems that operate on current solar energy. These are homesteads, farms and schools fit for a challenging future of peak oil, climate change and economic transition."
By running water through a giant compost pile, it was brought from 7 °C to a blistering 62 °C. Not much more needs to be said that the video doesn't say. We love seeing stuff like this, if you come up with your own brilliant backyard inventions or hear of one, by all means tip us off.