Question

- what is the mystery, the secret of terracotta stoves excellent heat retention ?

Answer 1

I don't know, but most insulating materials get their properties from trapped air, because the little cavities filled with air do not conduct heat well. There is very little mass in them (compared to the solid material around them) so heat can flow through them by convection only slowly. The atoms and molecules of the air are also not in direct contact, through chemical bonds, so heat cannot flow through direct conduction (the wiggling of one atom causing its bonded neighbors to wiggle).

I would guess that perhaps there are many tiny trapped bubbles of air in the terracotta that give it this property. As evidence I adduce the fact that plain terracotta won't hold water -- it leaks through -- which strongly suggests channels and passages within it.

Answer 2

terracotta is mostly clay, an aluminumoxide clade and reflects very well infrared light, that is I mean better at least than free air (which can conduct heat by convection, and thus cools the environment). Terracotta also has a big heat capacity, which means that it, once hot, will stay long hot (the heat capacity is comparable to the one of water, but terracotta on the other hand does not suffer from convection currents like water does)

Answer 3

Psychologically I thought terracotta can also count as a very natural matter, and calms the mind, and like that can make an effect of body relaxation, and thus less energy consumption and hence less heat loss. :)