Vallox 125 MV Vallox 125A R model is shown in the figure. In the L model, the parts are mirrored. 2a Heat recovery cell 3a Extract air fan 3c Supply air fan 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 (in front of the supply air fan) 6b Additional heating resistor 7a Safety switch 9a Ceiling bushing for electric wires 10a, 10b Control panel 11a Internal carbon dioxide and humidity sensor 11c Internal carbon dioxide and humidity sensor 11d Humidity sensor (optional) 11e VOC sensor (Optional)