The disclosure discloses a heating furnace including a housing, a first rack, a chamber, and at least one fan. The first rack is disposed in the housing. The chamber is disposed in the housing and located at a side of the first rack. The chamber includes an inlet, a first sidewall, and a second sidewall. The first sidewall is adjacent to the first rack. The first sidewall has a plurality of vents. The first sidewall and the second sidewall are disposed to face each other. A width is spaced between the first sidewall and the second sidewall, and the width is larger than or equal to 200 mm. The fan is disposed in the housing for generating an airflow to the inlet.