Vallox 90 MV R model in the figure. In the L model, the parts are mirrored. 1 Extract air fan 2 Supply air fan 3 Fine filter for supply air 4 Heat recovery cell 5 Bypass damper of the HR cell 6 Coarse filter for supply air 7 Coarse filter for extract air 8 Post-heating resistor 9 Safety switch 10 Internal humidity sensor Internal carbon dioxide sensor 11 Control panel 12 Carbon dioxide sensor (optional) 13 Humidity sensor (optional) 14 VOC sensor (optional)