A horizontal cooler reduces the temperature and moisture of hot pellets by conveying them along a horizontal moving bed or belt while ambient or conditioned air is drawn or blown through the product layer, typically in a cross-flow arrangement rather than the counter-current flow used in counterflow coolers. The product bed depth and belt or conveyor speed determine residence time within the cooling zone.

Horizontal coolers are often selected where floor space allows a longer footprint in exchange for a lower overall height than a vertical counterflow design, or in applications such as pet food and aquafeed production where gentler handling of larger or more fragile extruded or pelleted products is preferred. Some designs also allow easier visual inspection and access to the product bed during operation.

Multi-stage horizontal coolers, where product passes across two or more separate cooling sections in sequence, are common in applications requiring more controlled or gradual cooling — particularly for extruded products where rapid temperature change can affect product structure or surface finish, or where a final drying stage with a different air temperature is desired after initial cooling is complete.

Because air flows across rather than counter to the product, horizontal coolers are generally considered somewhat less thermally efficient per unit of airflow than counterflow designs, though this is often offset by advantages in product handling, layout flexibility or maintenance access depending on the specific plant requirements.

Belt or conveyor speed is the primary operational control for adjusting residence time in a horizontal cooler, with most designs allowing variable speed control so operators can adjust cooling duration to match changes in production rate or pellet/extrudate specification without needing to physically alter the equipment.

As with other cooler designs, even air distribution across the full width of the product bed is critical to consistent cooling performance, and horizontal coolers are particularly susceptible to "channeling" — where air preferentially flows through lower-resistance areas of an unevenly distributed product bed — making proper product spreading at the cooler inlet an important design and operational consideration.