Engineering:Kitchen hood

Short description: Type of home appliance that clears smoke from a stove

A kitchen hood in a small apartment

A kitchen hood, exhaust hood, hood fan, extractor 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 , as a range hood in the United States , and as a rangehood in Australia . It is also called a stove hood, hood fan, cooker hood, vent hood, or ventilation hood. Other names include cooking canopy, extractor fan, fume extractor, and electric chimney.

Description

An extractor hood consists of three main components: a skirt or capture panel to contain the rising gases (also known as the "effluent plume"), a grease filter, and a fan for ventilation.

Extractor hoods may be ducted (or vented) or ductless (or recirculating). Ducted hoods blow the gases to the outdoors; ductless hoods filter the air, often using activated charcoal, to remove odor and smoke particles from the air and then release the cleaned air back into the kitchen.

A ducted system removes of all forms of airborne contamination, while a ductless one recirculates heat and moisture. 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 or cooling the make-up air.

Exhaust hoods almost always include built-in lighting to illuminate the cooking surface. 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

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.

Filters

A very dirty mesh filter (top) and the same filter after being cleaned in a dishwasher

Filters remove most odors and particulates, including grease, from the vented air. There are three main types of filter:

• Mesh or cassette filters are made from aluminium mesh strips placed one over the other. They are highly effective in the capture and removal of oil and grease from smoke of both ducted and ductless chimneys. They must be cleaned regularly.
• Baffle filters are made of steel/aluminium frames with curved panels. The curves catch on grease, oil and other particulates. They are durable and easy to clean and are used in both ducted and ductless chimneys. They must be cleaned regularly.
• Charcoal filters are made of fine powdered activated charcoal. They are primarily used for ductless applications. They cannot be cleaned, but need to be replaced regularly.

Hood overhang

Greater hood overhangs are suggested to help contain cooking fires in the hood area protected by the fire suppression system.

Noise levels

Loud kitchen hoods can affect well-being, and may even contribute to hearing loss. Variable speed fans are generally noisier at higher speeds and different models may have different noise levels. Vented hoods are generally noisier but more effective than recirculating hoods.

Noise levels are measured on dB(A) scale or in sones (in the U.S.). Most kitchen hoods produce 60-70 dB(A), while "quiet" models can go as low as 40 dB(A).

Noise levels are generally given for the maximum speed, so it may be useful to compare noise levels at specific flow rates.

The European Union standardizes the measurement of hood noise.

Flow

Hood air flow is measured in liters per second (L/s), cubic meters per second (m³/s), or cubic feet per minute (cfm).

See also

• Fume hood
• Kitchen ventilation
• Smoke canopy

External links

• Article: "Oversized Kitchen Fans--An Exhausting Problem" by Bruce Manclark in Home Energy Magazine Online January/February 1999