Nobody wants to see rangehood ducting in their kitchen so it's always hidden away. This doesn't mean however, that it's not vitally important. If your cooker hood isn't vented correctly it wont work properly and will be more noisy. The noisier your rangehood the less likely you are to use it.
In any ventilation installation the aim is to move air efficiently and as quietly as possible to the outside. All ducting causes air resistance due to friction so it makes sence to reduce the length of duct as much as possible and minimise any unnecessary obstructions such as bends, constrictions and back-draft dampers. The longer the run and the more the obstacles such as bends and constrictions and sticking back-draft flaps, the more turbulance and back pressure will be caused, resulting in less efficiency and more noise.
The pictures below show how the back-draft flaps of the rangehood close when it's switched off to prevent air being pushed back through the ducting by wind pressure.from the outside and open to allow cooking fumes to escape. These are often taped shut in the factory to prevent damage and it's surprising how many installers forget to free them. Another reason for them not opening properly is the floppy duct that too many installers use the cheapest and nastiest duct they can buy. Floppy flexible duct is liable to prevent the flaps from opening properly in the first place, the ridges and folds within the duct cause severe air turbulance that in turn reduce airflow, increase back pressure and creates more noise.
A rangehood silencer or muffler will reduce significantly the noise generated by your rangehood. It is placed first in the ducting line directly attached to the rangehood where the air exits: the noisiest part. Ducting kits are available that incorporate a muffler, such as Rangehood Tamer.
1. Choose the shortest and most direct route from the rangehood to the outsde where the cooking fumes exit.
2. Ensure that bends constrictions and obstructions are kept to a minimum.
3. Check that you are using the correct duct size for the rangehood. Bigger is OK but smaller is definately not
4. Use good quality ducting, avoid floppy flexible duct and always cut away excess duct.
5. If flexible duct must be used, avoid the floppy (nude) kind, ensure that excess lenth is removed it's kept taught and doesn't interfere with the backdraft flaps.
6. Use a muffler in the air line, preferably attached to the rangehood but otherwise as close as possible.
Ducting a wall mounted rangehood generally means venting through either the wall, roof or soffit for which there are convenient kits.
Wall venting is suitable for both rear vented and top vented rangehoods and canopies. Probably the simplest way to vent a rangehood mounted on an outside wall.
With no acute bends to cause back pressure, roof venting is the most efficient way to vent a rangehood. Roof venting allows the rangehood to operate to its full capacity.