Downdraft Extractor Rangehood Systems
Downdraft ventilation is a range of ingeniously concealed extractor systems that provide an alternative to the conventional rangehood. The downdraft system works by drawing the air down through the benchtop or wall behind the hob to ventilate the kitchen. It’s invaluable for situations where a wall mounted rangehood is nort an option but it also has the advantage of eliminating the irritating ear-level noise of a standard rangehood.
Downdraft systems offers flexibility to the kitchen designer, being able to be installed virtually anywhere a hob can be positioned. Including under a window or within an island benchtop, in which case the need for an intrusive ceiling mounted canopy is eliminated.
There are several downdraft extraction systems available:
Rear or Side Riser
A riser unit can be positioned at the back or to the side of a cook top Or even in-between two hobs. In use the riser glides up into position to provide effective ventilation of the cooking area. In the case of riser venting, air is normally drawn down. It could be taken up of course but with some loss of suction if using a smaller fan motor. For roof or soffit ducting a bigger fan motor with a capacity of 1000 M3 p.h would be indicated. Take professional advice before choosing your system to ensure optimum performance.
Riser Venting Options:
In-bench downdraft
The under-bench air box is positioned under an aperture to draw air down and out. An attractive grill and surround finishes the benchtop aperture. Installation is simple and straightforward with the grill being easily removed for cleaning. With in-bench systems the air is usually take down though it could be taken up but with some loss of suction. Where roof or soffit venting is preferred the larger P-1-9 motor would be indicated.
In-Bench Downdraft Options
In-Wall Downdraft
The in-wall air box is fitted into the wall cavity where it remains unseen apart from the grill covered aperture. From here, air is drawn away by an unseen motor up, down or sideways to the external vent.
In-Wall Venting Options
Common Installations
The most common installations of in-bench downdraft are shown here:
For ventilating are larger space a fan motor with an air movement capacity of 750 -1,000 M3 p.h. or more is recommended. Remember to install a fan speed controller such as a dimmer switch so that you can control the air speed at any given time.
Ventilation Principles
Downdraft systems work on the principle of pulling air down faster than it rises from the cooktop. Steam and vapours rise at a maximum of 1m per second so to be effective, downdraft systems are designed to interrupt the rising fumes by drawing air down faster than it can rise. Depending on the system a the downdraft will be at 3-4 times the speed of the rising fumes to be effective.
Remember that any rangehood installation should ventilate the room effectively. It is the continual change of air in the room that keeps the environment fresh, preventing lingering cooking odours and condensation and in the case of a gas ho, remove combustion gases. Aim for a change of air at least ten times per hour. Calculate room size by floor area X ceiling height to find the volume of the room. The motor should be rated at 10 times the volume.
Where Buy A Downdraft System
Downdraft extractors are normally designed into kitchens by the kitchen designer but you can choose your own system and even save money by buying online. The only online downdraft specialist retailer in New Zealand is ApplianceSmart. Check out their website for more information by clicking here.
Kitchen ventilation advice for New Zealand kitchens
Copyright Tom McKernan 2017