Induction downdraft hobs requirements (Bora etc)

[PeterW]

3 hours ago, puntloos said:

Can someone explain why ducting hot air from the hob extractor directly into MVHR is a bad idea?

Airflow. 
 

Your average MVHR unit moves 300cuM/h on boost. The Bora on boost does that on its own. Blowing that into the MVHR will overwhelm the fan unit and you’ll just push air into the bathrooms etc as it will hit the plenums and the MVHR won’t be able to cope. 
 

Notwithstanding the grease issue, it’s just a really crap idea to try and blow air into a common extract system.