Is there Air Movement, Drafts, or Restrictions in the Room?

Any other air movement devices such as ceiling fans, air conditioner registers, etc., can create air currents which interfere with down draft ventilation.

Make-up air:

The air that is exhausted by the unit must be replaced.  If a room or house is too "tight", the unit may not vent properly.  If a house or room is too "tight", it will be necessary to introduce more air into the environment.  Some air conditioning and heating units allow for make-up air.

Adjacent cabinets:

Cabinets that are closer than the minimum distance allowed can create dead air pockets that impair performance.  For maximum performance, the recommended distance to adjacent cabinets or walls is 6". 

Refer to Installation Instructions for complete details.