Valheim actually gets it wrong. A fermenter is the active agent such as yeast, which generates the fermentation process. A fermentor is the vessel in which fermentation takes place. That being said, I did not place mine near my hearth either, but not because I was thinking it seemed unsafe. Now if it was a distiller, there is cause for worry. The alcohol content of the liquids present during fermentation is so low there is very, very little danger or flammability due to an open flame.