No, no plant roots overheating detected! The soil is in fact cold to the touch. There is about 60cm of sandstone above the flue, and soil is on the sandstone.
But, the flue doesent only heat up, it allso heats down and sideways. This means the flue heats about 10m3 of sandstone, wich is s lot of mass to heat, but allso s lot of mass to cool at hight.