We often have to correct the mistakes of others and remove burned-out flues. As a result, accumulated a whole collection of photos.
That's what happens when the furnace with wood, coal with flues made of stainless steel grades:
Therefore, we use only the correct stainless steel AISI 321 with titanium (08X18H10T) of 1 mm thickness and above. This stainless steel is acid and heat-resistant, so it is good and can withstand the heat and condensation.
Stainless steel should be labeled and have a certificate.
You can not skimp on their safety. Proper flue - in the right house.