Last winter while troubleshooting a pesky oil furnace (infernal, dirty beasts in my opinion), I came across these plans for a furnace that can be built for around $200-$300 in materials. It's fuel is compost, (grass clippings, hay and straw among others) and can provide as much as 90,000 Btu/hr, far more than most homes would likely ever need, with hot water supply as well. The plans are free to use and while I haven't dug into all the details, it seems a complete guide to building one. Once built, you load it with compost( grass clippings, hay and many other organics) and a handful of dirt and you've got a very green, low cost furnace.You need a good supply of compost, as it "burns" about 400 pounds in 3 or 4 days in colder winter climates. That all sounded like an infomercial but I thought some specifics were needed to give anyone interested a general idea about it. If I can find time I'd love to get started on one. Here is the page with the plan/guide:http://mb-soft.com/public3/globalzl.html I'd be curious if anyone builds one to know how it went.