Choosing a Range Hood, Vent Hood, Kitchen Hood, Kitchen Ventilation - Tips from an Expert | KitchenSource.com

Venting downwards has come a long way in the last 20 years and is mostly used in kitchen island or peninsula situations. This type of unit can also be used for a cooktop near a wall. But why? The fumes are drawn downwards under the floor and out (like for a clothes dryer) or into a basement and out. A lower powered model, suitable for an electric or small gas range top, often has the power pack placed in the cabinet beneath. A higher powered unit is usually placed in the basement and thus avoids the loss of storage an in-cabinet model may cause in a kitchen cabinet. Of course, you may choose to put lower powered units in the basement too to avoid this loss of storage.

Downdraft units are relatively inefficient because they have to fight the natural upwards flow of air and are most often used in an island situation if you don't want to block a view - or if your range top needs to be placed in front of a window.

Some downdraft models run from the front to the back of the countertop and are mostly used between modular stove tops; others have their vents at the back edge of the stove top but will not fit whenever a full size range top is in use (unless the countertop is increased in depth).