Vallox 51K 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 Control panel (optional) 10 Internal humidity sensor Internal carbon dioxide sensor 11 Humidity sensor (optional) 12 Carbon dioxide sensor (optional) 13 VOC sensor (optional) 14 Cooker hood 15 Damper button 16 Fan speed adjustment 17 Light switch 18 Ceiling bushing for electric wires (optional)