Choosing the right Rangehood

Choosing the right Rangehood Choosing the right Rangehood

Rangehood is a generic term that covers a variety of kitchen ventilation and air extraction systems.

  • Rangehood: Generally refers to a simple wall mounted appliance that is installed over the hob to either extract air to the outside or recirculate it via filters.
  • Canopy Rangehood: Refers to a more elaborate appliance that has a decorative chimney cover to the ceiling to hide the flue. Canopy rangehoods are much more powerful that the simple wall mounted models and provide a focal point in the kitchen.
  • Built-in or Integrated Rangehood: Extractors can be built into kitchen cabinets to hide them or under them, where they are less intrusive. Some. like the Tilta Hood can be fitted with a panel that matches the kitchen cabinets. The extraction device that fits into the cabinet is called a power pack and is operated from underneath.
  • Downdraft: Overhead rangehoods are not the only way to remove cooking vapours and odours. Downdraft rangehoods or extractors create a downward flow of air to effectively ventilate the hob. To learn how downdraft systems work, click here.


Positioning Your Rangehood

In New Zealand a rangehood must be at least 750mm above gas hobs and 600mm above electric hobs. Apart from those requirements your ventilation system can be set to suit yourself. Do bear in mind though that the effectiveness of a rangehood is dictated by its ability to move air rather than the precise height or how many filters it has.


Extraction vs Recirculation

Many extractors offer the alternatives of external ducting, where fumes are extracted to the outside, or recirculation where fumes are cleaned by filters and returned to the kitchen. All rangehoods will have a grease filter that removes some of the oils from cooking. For recirculation, a carbon filter can also be installed, which removes odours and finer particulates from the cooking fumes. The grease filters can be cleaned with detergent or in many cases in the dishwasher. Carbon filters will have to be changed regularly as they will become clogged, especially if a lot of oil is used in cooking.

Extraction of air to the outside has several benefits including:

  • Removal of cooking fumes such as steam, oils, smoke and odours.
  • Removing steam helps to prevent condensation
  • Removing cooking oils, which are present in the steam, prevents them from settling on surfaces and furniture.

Recirculation has some drawbacks including:

  • Steam remains inside where it might produce condensation.
  • Cooking oils will remain to settle on surfaces and furniture
  • Extra cost of replacing the carbon filters at least annually (or more depending on use)

On the other hand, recirculation might be the only option if space or building design makes the installation of external ducting difficult or impossible. If so it makes sense to use carbon filters to clean the air as much as possible and to change them regularly.


Extraction Rate

You should aim for a minimum of 10 x air changes per hour in your kitchen. To work out the extraction required for your kitchen space use the following formula: Cubic capacity of room in metres x 10. In other words if your kitchen is 6m long x 3m wide x 2.4m high, your space is 6 x 3 x 2.4 = 43.2 cubic metres. So your extractor needs to move at lease 43.2 metres ten times per hour, so it must have a minimum extraction rate of 440 cu.m. per hour. It's worth bearing in mind that a rangehood is more noisy at high speeds so it's worth getting one more powerful than necessary so you don't have to operate it flat out. You also need to keep running it for a few minutes after you finish cooking so, if you're sitting down to eat and don't want to listen to it, turn down the speed. Even better to buy one with a timer so you can set it to turn itself off after a few minutes.



Nobody likes to listen to a noisy rangehood but some noise is inevitable. Even with remote motoring air passing through the filters and ducting will produce noise. We have conducted in-house research and find that some rangehoods are much quieter than others of course but also that the decibel ratings given can be misleading. A typical budget rangehood will produce noise levels of around 60dB. This level of noise is obtrusive and unwelcome. On the other hand some models are relatively quiet in operation. But what is quiet? In our opinion you can reasonably expect a good rangehood to perform at under 50dB (measured at rangeood height at a distance of 1m. Normal conversation is approx. 60db. Click for more information about noise and decibels.

Remember that bad ducting can actually increase the noise from your rangehood. Flexible ducting is commonly used in rangehood installations but it has a rough, uneven surface that produces turbulence and back pressure so should be avoided at all costs.



Unless you choose the recycling option, you'll need to purchase ducting. Ducting kits aren’t supplied with rangehoods as standard but we do have a full range of ducting products including wall, soffit and roof venting kits. Some rangehoods will arrive with a length of flexible plastic ducting but it's not wise to use it as it doesn't comply with NZ building regulations, which require a flame and heat resistant product to provide fire protection for the wall or loft space.

If noise is an important factor for you, avoid metalised plastic flexible ducting at all costs. Metalised plastic flexible ducting is fine for slow moving air such as in HVAC systems but has an uneven surface and doesn't hold its shape well, which causes turbulence, restrictions and back pressure. Flexible ducting is a common cause of problems with rangehood installations. Use rigid or semi-rigid ducting when possible.