ActivPanel 4 (55" and 65" only) may be used horizontally, provided there is at least a 10cm clearance around the air vents to ensure proper airflow. Please consult article 1477 to check which version of ActivPanel you are using. 

All other versions and sizes of ActivPanel must be used vertically. No warranty is provided for products that are not used or installed in accordance with the installation and user guides.