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A kitchen hood, exhaust hood, or range hood is a device containing a mechanical fan that hangs above the stove or cooktop in the kitchen. It removes airborne grease, combustion products, fumes, smoke, heat, and steam from the air by evacuation of the air and filtration. In commercial kitchens exhaust hoods are often used in combination with fire suppression devices so that fumes from a grease fire are properly vented and the fire is put out quickly. Commercial vent hoods may also be combined with a fresh air fan that draws in exterior air, circulating it with the cooking fumes, which is then drawn out by the hood.
In most exhaust hoods, a filtration system removes grease (the grease trap) and other particles. Although many vent hoods exhaust air to the outside, some recirculate the air to the kitchen. In a recirculating system, filters may be used to remove odors in addition to the grease.
The device is known as an extractor hood in the United Kingdom and Singapore, as a range hood in Canada and the United States, and as a rangehood in Australia and New Zealand. It is also called a kitchen hood, stove hood, exhaust hood, cooker hood, vent hood, or ventilation hood. Other names include cooking canopy, extractor fan, fume extractor, and electric chimney.
An extractor hood consists of three main components: a skirt or capture panel to contain the rising gases (also known as the "effluent plume"), one or more grease filters, and a fan or tangential blower for forced ventilation.
There are two major configurations of extractor hoods: ducted (or vented) application, and ductless (or recirculating) application. In a ducted application, the output collar of the extractor hood's blower motor is attached to a duct system, which terminates outside the building. In a ductless application, a filter, often containing activated charcoal, removes odor and smoke particles from the air before releasing the cleaned air back into the kitchen.
A ducted system allows for the removal of all forms of airborne contamination, while a ductless one recirculates heat and moisture into the kitchen. In addition, a ducted application eliminates the need for regular replacement of the filters and avoids the airflow restriction (and the resultant loss of power) caused by them. However, the ducted application can be impractical, due to lack of space or ability to install a duct system, make-up air requirements, or the additional cost of heating/cooling the make-up air. Some range hood designs allow for both types of applications.
Exhaust hoods almost always include built-in lighting to illuminate the cooking surface. In addition, some manufacturers offer matching accessories, such as backsplash panels, pot racks, shelf units, or dish racks. The main advantage of an extractor hood is that it can easily filter the airflow, without harming the edible materials and can be easily installed if it is semi-automatic.
Extractor hood controls are typically electronic, though some low-end models use electromechanical controls. Extractor hoods with electronic controls can offer remote control, motorized height adjustment, thermal sensor, overheat protection, boost mode, delayed shut-off, filter cleaning reminder, active noise cancellation, temperature display, user presets (memory), and so on.
Extractor hoods may be made from a variety of materials, including stainless steel, copper, bronze, nickel silver, zinc, tempered glass, wood, aluminum, brass, heat-resistant plastics, and more.
NFPA 96 Standard for Ventilation Control and Fire Protection of Commercial Cooking says that mesh filters shall not be used. It requires that "Listed" grease filters shall be tested in accordance with UL 1046, Standard for Grease Filters for Exhaust Ducts.
Types of kitchen hoods
Kitchen hoods are broadly classified into ducted hoods and ductless hoods. This classification of these kitchen hoods is done purely on the basis of how the hoods process the air that is being sucked in.
Ducted kitchen hoods
Ducted kitchen hoods are the most common and a primary type of kitchen hood. As the name suggests, a ducted kitchen hood has a duct that is used to process and expel any smoke that is generated on top of the kitchen hob.
Large sized duct hoods are widely used not just in homes but also in commercial restaurants and communal kitchens too.
Ductless kitchen hoods
Ductless kitchen hoods do not have a duct that is used to process the air. Instead, it makes use of strong air filtration and then pumps out the air back into the room. These types of range hoods are usually used in houses.
A filter is pertinent to a kitchen hood as it helps in filtering the odours that are generated while cooking. A filter will take in all the odour, the dust and dirt that passes through the hood and clears out the airways.
Types of filters
Broadly, kitchen hood filters are available in three different types.
Also known as cassette filters, mesh filters are made from aluminium mesh strips placed one over the other in succession. They are highly effective in the capture and removal of oil and grease from smoke of both ducted and ductless chimneys. With the volume of filtration being high, these types of filters need to be cleaned once every week.
These type of filters are made out of steel/aluminium frames with curved panels. The curves in these panels are capable of catching up on grease, oil and other such particulates. Highly durable and easy to clean, they need to be cleaned once every month and are used in both ducted and ductless chimneys.
Charcoal filters are made out of fine powdered activated carbon charcoal that is in a honeycomb structure. Used primarily in a ductless chimney for the filtration of odors, a charcoal filter has no cleaning method and is usually replaced once every 6 months or so.
Cleaning kitchen hood filters
A kitchen hood filter gathers up dust and dirt all along while it is clearing it out. This will decrease the quality of air that is being filtered out regularly. Hence, for a better performance of the kitchen hood, the filter must either be replaced or cleaned once every fortnight.
In order to clean a kitchen hood filter, the simplest method is to use baking powder. For this, the hood filter is placed in a large pot of water, drop in half a spoon of baking powder. This pot with the filter and the baking powder is now heated to boil on a stove. As the water boils, the grease and the dirt can be seen being removed slowly and steadily.
Greater hood overhangs are suggested to help contain cooking fires in the hood area protected by the fire suppression system.
Noise from kitchen hoods can affect the well-being when working at the kitchen, or may even contribute to hearing loss if used regularly over a long time. Fans with variable speed settings usually create more noise at their higher settings which often correspond to higher air volume flow rates. Different types and models can have different noise levels when transporting the same air volume. Extraction hoods which vent to the outdoor are usually more noisy but also more effective removing air, while recirculation hoods often are quieter but less effective at removing smells and pollution.
As with other kitchen appliances, noise levels of kitchen hoods are often measured on the logarithmic decibel scale with A-weighting, abbreviated dB(A). As of 2020, one source cite the noise level from the majority of kitchen hoods being marketed with 60-70 dB(A), while "quiet" models for example can go as low as 40 dB(A), and with loud models being loosely classified as models which produce noise levels over 70 dB(A). Another source cites 50 dB(A) as a "quiet" kitchen hood.
Noise levels are generally advertised at the maximum speed, and it may therefore be useful to compare noise levels at various volumetric air flow rates (for example in liters per second) to get a more nuanced picture. Internationally, air flow in kitchen hoods are usually measured in liters per second (L/s), but can also for example be measured in cubic meters per second (m3/s), cubic feet per minute (cfm) or U.S. gallons per second (US gal/s).
The European Union has regulations standardizing measurement procedures of kitchen hood fan noise. In the U.S., noise levels of kitchen hoods are sometimes measured in "sones" instead of decibels. Approximate conversion tables between decibels and sones exist.
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