I’ve looked with interest at the heatgreen compost system 3a. It does look very impressive - I do wish there was an open forum available at its site, for others to discuss builds and issues. It seems as though this aspect is holding back larger scale adoption. I have not built one, but have considered it!

I also notice that there is a simpler smaller 4a device now shown on the same site. It avoids building a watertight inner bag, and rotating the whole system. Instead, it uses a wheelie bin, and a large corkscrew mechanism for stirring. Similar levels of insulation are used for both - 4inches of polystyrene. Below is a link to the 4a page:

http://mb-soft.com/public4/globalwarmingz.html

It’s not clear to me, but I believe he places the 4a in a basement, and directly uses the hot air From the device as a heatsource for his house.