Vallox 145 MV R model in the figure. In the L model, the parts are mirrored. 2a Heat recovery cell 3a Extract air fan (behind the protective cover) 3c Supply air fan (behind the protective cover) 4a Fine filter for supply air 4b Coarse filter for supply air 4c Coarse filter for extract air 5a Bypass damper of the HR cell 6a Post-heating resistor (behind the extract air duct) 7a Safety switch 9a Ceiling bushing for electric wires 10a 10b Control panel 11a Internal humidity sensor Internal carbon dioxide sensor 11c Carbon dioxide sensor (optional) 11d Humidity sensor (optional) 11e VOC sensor (optional)