This kind of design is widely used for services requiring horizontal tube arrangement (for specific flow pattern requirement) and for duties in the range of 30-120 MW. In the radiant section (cabin shape) the tubes are arranged horizontally along the side walls and the sloping roof of the cabin (on the front wall no tubes are installed). The firebox can be composed by a single cabin cell or double cells according to the size and number of passes. Tipically convection section extends over the entire length of the radiant section. Horizontal tube arrangement requires higher plot area (for tube extraction) but allows coil drainability (by gravity) and easier access to radiant return bends (seldom located inside radiant header boxes) for inspection and maintenance purposes. Burners are floor-mounted, installed in a row placed in the center-line of the cabin and fired vertically. Thus, firing is generally normal to both radiant and convection tubes.
Sometimes, with small duties, burners are instead located in the front walls opposite side firing horizontally toward the center of the firebox. This kind of design is typically suitable for Topping and Vacuum services, Crude Heaters, Reboilers, Heavy Feed preheaters.