By using original Zehnder filters, you can ensure that your ventilation unit is operating as designed. The accessory filters available on the market may fit the unit in size and shape, but often their material does not match the original filters. In this case, the filters may not function as intended. Different pressure drop from original filters may increase air leakage through house structures, thus reducing heat recovery and introducing various impurities into the room air. In addition, it can cause moisture to build up in structures and, at worst, mold damage.