Fired heater

ISO 10628-2 (groups 3-5, heat exchangers, furnaces, cooling towers) / PIP PIC001 / TEMA (group 4) / API 560

Drawn as

A tall box (radiant section) with burners (small flames or triangles) along the floor, a narrower convection box above, and a tapered stack on top. A coil (zig-zag) runs through.

Meaning

Direct-fired process heater: hot-oil heaters, glycol reboilers, crude heaters (mostly onshore). Becomes fired-heater.

Variants

Simplified: a rectangle with a flame triangle under it
Box vs cylindrical heaters look similar on P&IDs