BBQ Rangehoods generally need to exhaust 2000m3/hr to be recognized as a genuine BBQ Rangehood.
An Inline Motor (Located in the Flue or in the roof cavity) may only exhaust 1600m3/hr Gross & be extremely efficient
The fact that a BBQ Rangehood may exhaust 2600m3/hr ( 1200mm Rangehood) or 3900 on a (1500mm
Rangehood) can be immaterial. You maybe just adding to noise!
The higher the Airflow the more difficult it become to Exhaust.
The venting needs to have no obstructions,
The quality of the Ducting used needs to be either Sermi Rigid or Solid Ducting.The Roof Cowel used needs to one
which is completely open all the way round to allow the Air to Escape.
If the Ducting is not done correctly or incorrect Ducting is used the risk is that BACKDRAFT will occur!
Backdraft is wheremost of the Exhausted air cannot escape to the Outside & is pushed back down the Rangehood.
It is always desirable to Duct through the Roof