Finnish 
Allergy filters Swegon CASA W3 / W4 W304FSF8
Product description
Allergy filters for W3 and W4 units when cleaner supply air is required.
Filter class ISO ePM1 70 % (F8) for supply air and ISO coarse (G3) for extract air. It should be noted that a separate setting of the unit is necessary and that filters must be replaced more often than standard filters.