Abstract: A conveyor furnace for heat treating a regular succession of articles consists of a circular carrier mounted for rotation about an upright axis below a fixed guide of open coiled spiral configuration and fixed radiant heaters directed through parts of the guide. A feed tube delivers the articles to an inner part of the guide on to the carrier whereon they are carried in sliding engagement with the guide, around and progressively outwards towards a discharge point. While on the carrier, the articles are heated by the heater. The furnace is compact, economical in operation and permits of relatively simple and reliable construction.