For the distribution of the air we deliver half round ducts. These ducts are made in as many as 20 different sizes. This has the advantage, that the different duct-parts connect easily. The oblong holes are mostly positioned low, close to the ground to distribute the air widely. To also aerate the top well, there are rows of holes on the top side of the duct parts.
All holes are forced inwards, so that there are no sharp edges that could cut into the potatoes or onions.