Downdraft rangehoods are sometimes a necessity such as when a hob is situated under a window and it isn't possible to install a canopy but they are also chosen for aesthetic reasons. Not everyone likes bulky rangehood canopies, especially when hanging down from the ceiling. The downdraft option offers a discreet way of providing ventilation and removing cooking odours.
The most common question we are asked about downdraft extraction systems is: 'How is it possible to capture rising steam and cooking vapours from below?'
Although It seems to impossible to capture rising vapours that have already escaped above the hob and logical that you must have some sort of canopy to capture the vapours above the hob before extracting the upwards, simple physics belies this as explained below.
Cooking steam and vapours rise at a maximum speed of 1 metre per second. To interrupt this process and draw the vapours down a faster downward airflow needs to be generated.
A downdraft system causes a downward flow of air which, at between 3 and 4 metres per second will cause a cross effect.
When the correct airflow is achieved the crossflow effect comes into play and cooking vapours and odours are nipped in the bud by drawing them off where they arise: directly at the cooktop, from the saucepan, frying pan or griddle, not by magic, but by applying the basic principles of fluid mechanics. The downdraft system simply uses a cross flow of air that is greater than the rising speed of the cooking vapour.