Often portable, Ge 15:17. They were used for melting the precious metals, Pr 17:3. The furnace into which Daniel's three friends were cast was large, and remained open after they were cast in, Da 3. The fearful punishment spoken of in Jer 29:22 is still used in the East. The word furnace is used to illustrate a state of oppression, De 4:20, and of affliction, Isa 48:10.
And it came to pass, that, when the sun went down, and it was dark, behold, a smoking furnace, and a flaming torch that passed between these pieces.
But Jehovah hath taken you, and brought you forth out of the iron furnace, out of Egypt, to be unto him a people of inheritance, as at this day.
The refining pot is for silver, and the furnace for gold; But Jehovah trieth the hearts.
Behold, I have refined thee, but not as silver; I have chosen thee in the furnace of affliction.
American Standard Version Public Domain