A draw-through configuration refers to how the coils and the supply fan are configured in an air handling unit. In a draw-through configuration, the coils are installed upstream of (before) the supply fan. This means that they are installed on the “suction” side of the fan.
On the suction side of a fan, air is being pulled. The supply fan will “draw” air “through” the coils in this configuration.
If the coils and fan were to switch places, it would be a blow-through system. You can learn more about that by clicking here.
The image below shows a standard draw-through AHU configuration. Notice the fan would pull (or draw) air through the heating (red) and chilled (blue) water coils.