Albert Barnes Commentary Jeremiah 36:22

"Now the king was sitting in the winter-house in the ninth month: and [there was a fire in] the brazier burning before him." — Jeremiah 36:22 (ASV)

The winterhouse — A separate portion of the palace was used for residence according to the season (marginal reference).

And there was a fire on the hearth ... — and the fire-pan burning before them. On the middle of the floor was a brazier containing burning charcoal.