Zehnder EVO CO2 Sensor for use with EVO 2 3 4 0563 0401 Ideal for the long walks Ideal for the long walks on large sites and inner city calls outs This type of installation requires a more powerful motor as the extracted air will usually have further to travel than a standard through wall installation as it is typically fitted with the duct running in a loft space and out through the soffit The user can either manually select the desired ventilation system flow rate based on the visual air quality indicator or automatically adjust the unit relative to the CO2 level for on demand control CO2 measuring range 400 2000 ppm