Vallox TSK Multi 80 MV R model in the figure. In the L model, the parts are mirrored. 1 Supply air fan 2 Extract air fan 3 Post-heating resistor, electric, 900 W 4 Heat recovery cell 5 Fine filter for supply air 6 Coarse filter for supply air 7 Coarse filter for extract air 8 Bypass damper of the HR cell 9 Safety switch 10 Control panel 11 Internal humidity sensor Internal carbon dioxide sensor 12 Carbon dioxide sensor (optional) 13 Humidity sensor (optional) 14 VOC sensor (optional)