Energy Efficient Ceiling Fans

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A ceiling fan is a mechanical fan, usually electrically powered, suspended from the ceiling of a room, that uses hub-mounted rotating paddles to circulate air.

Most of the ceiling fans rotate much more slowly than most electric desk fans. They cool people effectively by introducing slow movement into the otherwise still, hot air of a room. Fans never actually cool air, unlike air-conditioning equipment, but use significantly less power (cooling air is thermodynamically expensive). Conversely, a ceiling fan can also be used to reduce the stratification of warm air in a room by forcing it down to affect both occupants' sensations and thermostat readings, thereby improving climate control energy efficiency.

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History

Punkah-type ceiling fans date back to 500 BC, and are native to India. Unlike modern rotary fans, these punkah fans move air by moving to and fro, and were operated manually by cord.

The first rotary ceiling fans appeared in the early 1860s and 1870s, in the United States. At that time, they were not powered by any form of electric motor. Instead, a stream of running water was used, in conjunction with a turbine, to drive a system of belts which would turn the blades of two-blade fan units. These systems could accommodate several fan units, and so became popular in stores, restaurants, and offices. Some of these systems still survive today, and can be seen in parts of the southern United States where they originally proved useful.

The electrically powered ceiling fan was invented in 1882 by Philip Diehl. He had engineered the electric motor used in the first electrically powered Singer sewing machines, and in 1882 he adapted that motor for use in a ceiling-mounted fan. Each fan had its own self-contained motor unit, with no need for belt drive.

Almost immediately he faced fierce competition due to the commercial success of the ceiling fan. He continued to make improvements to his invention and created a light kit fitted to the ceiling fan to combine both functions in one unit. By World War I most ceiling fans were made with four blades instead of the original two, which made fans quieter and allowed them to circulate more air. The early turn-of-the-century companies who successfully commercialized the sale of ceiling fans in the United States were the Hunter Brothers division of Robbins & Myers, Westinghouse Corporation and Emerson Electric.

By the 1920s, ceiling fans were commonplace in the United States, and had started to take hold internationally. From the Great Depression of the 1930s, until the introduction of electric air conditioning in the 1950s, ceiling fans slowly faded out of vogue in the U.S., almost falling into total disuse in the U.S. by the 1960s; those that remained were considered items of nostalgia.

Meanwhile, electric ceiling fans became very popular in other countries, particularly those with hot climates, such as India and the Middle East, where a lack of infrastructure and/or financial resources made energy-hungry and complex freon-based air conditioning equipment impractical. In 1973, Texas entrepreneur H. W. (Hub) Markwardt began importing highly efficient ceiling fans to the United States that were manufactured in India by Crompton Greaves, Ltd. Crompton Greaves had been manufacturing ceiling fans since 1937 through a joint venture formed by Greaves Cotton of India and Crompton Parkinson of England, and had perfected the world's most energy efficient ceiling fans thanks to its patented 20 pole induction motor with a highly efficient heat-dissipating cast aluminum rotor. These Indian manufactured ceiling fans caught on slowly at first, but Markwardt's Encon Industries branded ceiling fans (which stood for ENergy CONservation) eventually found great success during the energy crisis of the late 1970s and early 1980s, since they consumed far less energy (under 70 watts of electricity) than the antiquated shaded pole motors used in most other American made fans. The fans became very effective energy saving appliances for residential and commercial use by supplementing expensive air conditioning with a cooling wind-chill effect. Fans used for comfort create a wind chill by increasing the heat transfer coefficient, but do not lower temperatures directly.

Due to this renewed commercial success using ceiling fans effectively as an energy conservation application, many American manufacturers also started to produce, or significantly increase production of, ceiling fans. In addition to the imported Encon ceiling fans, the Casablanca Fan Company was founded in 1974. Other American manufacturers of the time included the Hunter Fan Co. (which was then a division of Robbins & Myers, Inc), FASCO (F. A. Smith Co.), Emerson Electric, and Lasko; the latter two were often branded as Sears-Roebuck.

Through the 1980s and 1990s, ceiling fans remained popular in the United States. Many small American importers, most of them rather short-lived, started importing ceiling fans. Throughout the 1980s, the balance of sales between American-made ceiling fans and those imported from manufacturers in India, Taiwan, Hong Kong and eventually China changed dramatically with imported fans taking the lion's share of the market by the late 1980s. Even the most basic U.S-made fans sold for $200 to $500, while the most expensive imported fans rarely exceeded $150.

Since 2000, important inroads have been made by companies such as Monte Carlo, Minka Aire, Quorum, Craftmade, Litex and Fanimation - offering higher price ceiling fans with more decorative value. In 2001, Washington Post writer Patricia Dane Rogers wrote, "Like so many other mundane household objects, these old standbys are going high-style and high-tech."

Energy Efficient Ceiling Fans Video

Uses

Unlike air conditioners, fans only move air--they do not directly change its temperature. Therefore, ceiling fans that have a mechanism for reversing the direction in which the blades push air (most commonly an electrical switch on the unit's switch housing, motor housing, or lower canopy) can help in both heating and cooling.

Some ceiling fans are mechanically reversible (have adjustable blade pitch) instead of an electrically reversible motor. In this case, the blade should be pitched to the right (or left if the motor spins clockwise) for downdraft, and left (or right if the motor spins clockwise) for updraft. Hunter Hotel Original is one example.

In summer, the fan's direction of rotation should be set so that air is blown downward (Usually counter-clockwise from beneath). The blades should lead with the upturned side as they spin. The breeze created by a ceiling fan speeds the evaporation of perspiration on human skin, which makes the body's natural cooling mechanism much more efficient. Since the fan works directly on the body, rather than by changing the temperature of the air, during the summer it is a waste of electricity to leave a ceiling fan on when no one is in a room unless there's air conditioning, open windows, or anything that can heat up the room (such as oven) and fan is just to move air around.

In winter, ceiling fans should usually be set to turn the opposite direction (usually clockwise; the blades should spin with the downward turned side leading) and on a low speed (or the lowest speed the fan is able to circulate the air down to the floor). Air naturally stratifies--that is, warmer air rises to the ceiling while cooler air sinks. Unfortunately, this means it is colder on or near the floor where human beings spend most of their time. A ceiling fan, with its direction of rotation set so that air is drawn upward, pulls up the colder air below, forcing the warmer air nearer the ceiling to move down to take its place, without blowing a stream of air directly at the occupants of the room. This action works to even out the temperature in the room, making it cooler nearer the ceiling, but warmer nearer the floor. Thus the thermostat in the area can be set a few degrees lower to save energy, while maintaining the same level of comfort. It is important to run the fan at a low speed (or a lowest speed the fan is able to circulate the air down to the floor) to minimize the wind chill effect described above. However if the ceiling is high enough, or the lowest speed downdraft would not create wind chill effect, it can be left on downdraft year around.

An additional use of ceiling fans is coupling them with an air conditioning unit. Through-the-wall/through-the-window air conditioning units typically found in rented properties in North America usually have both the tasks of cooling the air inside the room and circulating it. Provided the ceiling fan is properly sized for the room in which it is operating, its efficiency of moving air far exceeds that of an air conditioning unit, therefore, for peak efficiency, the air conditioner should be set to a low fan setting and the ceiling fan should be used to circulate the air.

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Parts of a ceiling fan

The key components of a ceiling fan are the following:

• An electric motor
• Blades (known as paddles or wings) usually made from wood, plywood, iron, aluminium, MDF or plastic
• Blade irons (alternately blade brackets, blade arms, blade holders, or flanges), which hold the blades and connect them to the motor.
• Flywheel, a metal or tough rubber double-torus which is attached to the motor shaft, and to which the blade irons may be attached. The flywheel inner ring is locked to the shaft by a lock-screw, and the blade irons to the outer ring by bolts that feed into tapped metal inserts. Rubber or plastic flywheels may become brittle and break, a common cause of fan failure. Replacing the flywheel may require disconnecting wiring and requires removing the switch housing that's on the way for the flywheel to be removed and replaced.
• Rotor, alternative to blade irons. First patented by industrial designer Ron Rezek in 1991, the one-piece die cast rotor receives and secures the blades and bolts right to the motor, eliminating most balance problems and minimizing exposed fasteners.
• A mechanism for mounting the fan to the ceiling such as:
  • ball-and-socket system. With this system, there is a metal or plastic hemisphere mounted on the end of the downrod; this hemisphere rests in a ceiling-mounted metal bracket and allows the fan to move freely (which is very useful on vaulted ceilings). Some companies have come up with slight modifications of this design.
  • J-hook (Claw hook) system. a type of mounting system where the ceiling fan hangs on a metal hook, attached to the ceiling. A rubber grommet is used to keep the fan in place and helps avoid vibration on the ceiling.
  • Some fans can be mounted using a low-ceiling adapter, a special kit which must be purchased from the fan's manufacturer. This eliminates the need for a downrod, and is therefore useful in rooms with low ceiling clearance.
  • In recent years, it has become increasingly common for a ball-and-socket fan to be designed such that the canopy (ceiling cover piece) can optionally be screwed directly into the top of the motor housing; then the whole fan can be secured directly onto the ceiling mounting bracket. This is known as a "close-to-ceiling" mount.

Other components, which vary by model and style, can include:

• A downrod, a metal pipe used to suspend the fan from the ceiling. Downrods come in many lengths and widths, depending on the fan type.
• A decorative encasement for the motor (known as the "motor housing").
• A switch housing (also known as a "switch cup" or "nose column"), a metal cylinder mounted below and in the center of the fan's motor. The switch housing is used to conceal and protect various components, which can include wires, capacitors, and switches; on fans that require oiling, it often conceals the oil reservoir which lubricates the bearings. The switch housing also makes for a convenient place to mount a light kit.

• Blade badges, decorative adornments attached to the visible underside of the blades for the purpose of concealing the screws used to attach the blades to the blade irons.
• Assorted switches used for turning the fan on and off, adjusting the speed at which the blades rotate, changing the direction in which the blades rotate, and operating any lamps that may be present.
• Lamps
  • Uplights, which are installed on top of the fan's motor housing and project light up onto the ceiling, for aesthetic reasons (to "create ambiance")
  • Downlights, often referred to as a "light kit", which add ambient light to a room and can be used to replace any ceiling-mounted lamps that were displaced by the installation of a ceiling fan
  • Decorative light bulbs mounted inside the motor housing--in this type of setup, the motor housing often has glass panel sections which allow light to shine though.

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Configurations

• Commercial or industrial ceiling fans are usually used in offices, factories or industries. Commercial ceiling fans are designed to be more cost effective and more energy efficient then other cooling alternatives. The industrial or commercial ceiling fans usually use three blades and operate with a high-speed motor. Some can be found with more than 3 blades though. These energy efficient ceiling fans usually push massive amounts of air compared to other ceiling fan types. In the 1980s, it was common to find metal-bladed industrial ceiling fans in American households, while industrial fans in household applications are still commonplace today in Middle-Eastern households.
• A hugger or low profile ceiling fan is usually installed on a low ceiling. They can also be used in rooms with vaulted ceilings when installed on the joist. In cold climates, a ceiling fan may disperse heat to warm up the room as well by dispersing downwards the warm air that rises to the ceiling surface. Though the ceiling fan cannot lower room temperatures, when used in tandem with a room air-conditioner it may be able to disperse the cool air all around the room.
• Outdoor ceiling fans are ceiling fans designed for outdoor purposes, they are usually water resistant and made of materials that do not get affected by outside temperatures, weather or humidity.
• Energy Star ceiling fans are manufactured under the Energy Star label. Usually energy star fans hold the distinction of being more energy efficient (50%), have lower price tags, and save a lot of money by using less electricity.
• "Mini" ceiling fans are mostly found in less developed places, such as the Philippines and Indonesia, and are made almost entirely out of plastic except for the inside of the motor, etc. These fans, hence the name "mini" ceiling fan are relatively small in size, usually ranging from 16 inches to 36 inches, however some still span to sizes as large as 42 inches in diameter. Additionally, unlike traditional ceiling fans, these fans usually use synchronous motors.

• Orbit fans are fans that use a mechanism to oscillate at 360 degrees. They are also typically flushed to the ceiling like hugger type fans. They are also very small in size, usually about 16" and have a similar construction to that of many pedestal fans and desk fans, and usually have finger guards. These are once again, popular mostly in many developing countries as they are a cheap alternative to traditional paddle type ceiling fans. Many American manufacturers, such as "Fanimation" have started producing high quality designer versions of such fans for their retro design, however, unlike the orbit huggers discussed earlier, these usually include downrods, like many early versions of the orbit fan.

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Operating a ceiling fan

The way in which a fan is operated depends on its manufacturer, style, and the era in which it was made. Operating methods include:

• Pull-chain/pull-cord control. This style of fan is equipped with a metal-bead chain or cloth cord which, when pulled, cycles the fan through the operational speed(s) and then back to off. These fans usually have three speeds.
• Variable-speed control. During the 1970s and 1980s, fans were often produced with a variable-speed control. This was a dial mounted on the fan which, when turned in either direction, continuously varied the speed at which the blades rotated--similar to a dimmer switch for a light fixture. A few fans substituted a rotary click-type switch for the infinite-speed dial, providing a set number of speeds (usually ranging from five to ten).
  • Different fan manufacturers used the variable-speed control in different ways:
    • The variable-speed dial controlling the fan entirely; to turn the fan on, the user turns the knob until it clicks out of the "off" position, and can then choose the fan's speed.
    • A pull-chain present along with the variable-speed control; the dial can be set in one place and left there, with the pull-chain serving only to turn the fan on and off. Many of these fans have an option to wire the light kit to this pull-chain in order to control both the fan and the light with one chain. Using this method, the user can have either the fan or light on individually, both on, or both off.
    • "Vari-Lo": A pull-chain and variable-speed control are present. Such a fan has two speeds controlled by a pull-chain: high (full power, independent of the position of the variable-speed control), and "Vari-Lo" (speed determined by the position of the variable-speed control).
• Wall-mounted control. Some fans have their control(s) mounted on the wall instead of on the fans themselves; such controls are usually proprietary and/or specialized switches.
  • Digital control. With this style of control, all of the fan's functions--on/off status, speed, direction of rotation, and any attached light fixtures--are controlled by a computerized wall control, which typically does not require any special wiring. Instead, it uses the normal house wiring to send coded electrical pulses to the fan, which decodes and acts on them using a built-in set of electronics. This style of control typically has anywhere from three to six speeds.

• • Choke. This style of switch takes varying physical forms. The wall control, which contains a motor speed regulator of some sort, determines how much power is delivered to the fan and therefore how fast it spins. Older such controls employed a choke--a large iron-cored coil--as their regulator; these controls were typically large, boxy, and surface-mounted on the wall. They had anywhere from four to eight speeds, typically four or five. Newer versions of this type of control do not use a choke as such, but much smaller capacitors or electronic circuitry; the switch is typically mounted in a standard in-wall gang box.
  • Solid state variable speed control. These controls, commonly used on industrial fans, can control more than one (up to 15) fans with one switch. 2.5 to 6 amp controls can typically be installed in "gangs" with other solid-state controls or standard light switches or wiring devices, while 8 to 15 amp controls have a large heat sink and cannot be "ganged" with other devices.
• Wireless remote control. In recent years, remote controls have dropped in price to become cost-effective for controlling ceiling fans. They may be supplied with fans, or fitted to an existing fan. The hand-held remote transmits radio frequency or infrared control signals to a receiver unit installed in the fan. However, these may not be ideal for commercial installations as the controllers require batteries. They can also get misplaced, especially in installs with many fans.

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Types of ceiling fans

Many styles of ceiling fans have been developed over the years in response to several different factors such as growing energy-consumption consciousness and changes in decorating styles. The advent and evolution of electronic technology has also played a major role in ceiling fan development. Following is a list of major ceiling fan styles and their defining characteristics:

• Cast-iron ceiling fans. Cast-iron ceiling fans account for almost all ceiling fans made from their invention in 1882 through the 1950s. A cast-iron housing encases a very heavy-duty oil-bath motor, usually of the shaded-pole variety. These fans must be oiled periodically, usually once or twice per year, since they use an oil-bath system for lubrication. Because these fans are so sturdily built, and due to their utter lack of electronic components, it is not uncommon to see cast-iron fans aged eighty years or more running strong and still in use today.

• The Hunter 'Original' (manufactured by the Hunter Fan Co., formerly a division of Robbins & Myers, Inc.) is an example of a cast-iron ceiling fan. It has enjoyed the longest production run of any fan in history, dating from 1906 to the present (it is still being manufactured). The Original employed a shaded-pole motor from its inception until 1984, at which point it was changed to a permanent split-capacitor motor. Though the fan's physical appearance remained unchanged, the motor was further downgraded in 2002 when production was shipped to Taiwan; the motor, though still oil-lubricated, was switched to a "skeletal" design, as discussed below. Then in 2015, when the model was revised, the motor got pre-2002 elements back, such as 4" main shaft. Post-2015 Original also has wood blades with PVC overlay for outdoor use, and therefore is damp rated.

• 20 pole Induction "Pancake" motor ceiling fans. These fans with highly efficient cast aluminum housings, were invented in 1957 by Crompton-Greaves, Ltd of India and were first imported into the United States in 1973 by Encon Industries. This Crompton-Greaves motor was developed through a joint venture with Crompton-Parkinson of England and took 20 years to perfect. It is considered the most energy efficient motor ever manufactured for ceiling fans (apart from the DC motor) since it consumes less energy than a household incandescent light bulb.
• Stack-motor ceiling fans. In the late 1970s, due to rising energy costs prompted by the energy crisis, Emerson invented a new style of electric motor designed specifically for ceiling fans, the "stack" motor. Along with Encon's cast aluminum 20 pole motor, this powerful, energy-efficient motor aided in the comeback of ceiling fans in America, since it was far less expensive to operate than air conditioning. With this design (which consists of a basic stator and rotor), the fan's blades mount to a central hub, known as a flywheel. The flywheel can be made of either metal or reinforced rubber, and can be mounted either flush with the fan's motor housing (concealed) or prominently below the fan's motor housing (known as a "dropped flywheel"). Many manufacturers used and/or developed their own stack motors, including (but not limited to) Casablanca, Emerson, FASCO, Hunter, and NuTone. Some manufacturers trademarked their personal incarnation of this motor: for example, Emerson came out with the "K-55" and "K-63" motors, Fanimation with the "FDK-2100", and Casablanca with the "XLP-2000". One of the earliest stack-motor fans was the Emerson "Heat-Fan", aka the "Universal Series", a utilitarian fan with a dropped metal flywheel and blades made of either fiberglass or plastic depending on the model. This fan was produced from 1976 through 1983 and, while targeted at commercial settings, also found great success in residential settings. Casablanca Fan Co. also made stack-motor fans with concealed flywheels rather than dropped flywheels. While this motor is not nearly as widely used as in the 1970s and 1980s, it can still be found in certain high-end Casablanca, Emerson, and Fanimation fans. One disadvantage of this type of fan is that the flywheel, if it is made from rubber, will dry out and crack over time and eventually break; this is usually not dangerous, but it renders the fan inoperable until the flywheel is replaced.
• Direct-drive ceiling fans employ a motor with a stationary inner core with a shell, made of cast-iron, cast-aluminum, or most commonly stamped steel, that revolves around it (commonly called a "spinner" motor); the blades attach to this shell. Direct-drive motors are the least expensive motors to produce, and on the whole are the most prone to failure and noise generation. While the very first motors of this type (first used in the 1960s) were relatively heavy-duty, the quality of these motors has dropped significantly in recent years. This type of motor has become the standard for today's fans; it has been (and is) used in all Hampton Bay and Harbor Breeze ceiling fans, and has become commonly used by all other brands.
  • Spinner fans employ a direct-drive motor and do not have a stationary decorative cover (motor housing). This accounts for most industrial-style fans (though such fans sometimes have more moderate-quality motors), and some inexpensive residential-style fans (particularly those made overseas).
  • Spinner-motor fans, sometimes incorrectly referred to as "spinners", employ a direct-drive (spinner) motor and do have a stationary decorative cover (motor housing). "Spinner-motor" fans account for nearly all fans manufactured from the late 1980s to the present.

• Skeletal motors, which are a high-quality subset of direct-drive motors, can be found on some higher-quality fans. Examples of skeletal motors include Hunter's "AirMax" motor, Casablanca's "XTR200" motor, and the motors made by Lasko for use in their ceiling fans. Skeletal motors differ from regular direct-drive motors in that:
  • They have an open ("skeletal") design, which allows for far better ventilation and therefore a longer lifespan. This is in comparison to a regular direct-drive motor's design, in which the motor's inner workings are completely enclosed within a tight metal shell which may or may not have openings for ventilation; when openings are present, they are almost always small to the point of being inadequate.
  • They are typically larger than regular direct-drive motors and, as a result, are more powerful and less prone to burning out.
• Friction-drive ceiling fans. This short-lived type of ceiling fan was attempted by companies such as Emerson and NuTone in the late 1970s with little success. Its advantage was its tremendously low power consumption, but the fans were unreliable and very noisy, in addition to being grievously underpowered. Friction-drive ceiling fans employ a low-torque motor that is mounted transversely in relation to the flywheel. A rubber wheel mounted on the end of the motor's shaft drove a hub (via contact friction, hence the name) which, in turn, drove the flywheel. It was a system based on the fact that a low-torque motor spinning quickly can drive a large, heavy device at a slow speed without great energy consumption (see Gear ratio).
• Gear-drive ceiling fans. These were similar to (and even less common than) the friction drive models; however, instead of a rubber wheel on the motor shaft using friction to turn the flywheel, a gear on the end of the motor shaft meshed with gear teeth formed into the flywheel, thus rotating it. The company "Panama" made gear driven ceiling fans and sold them through "Family Handyman" magazine in the 1980s.
• Internal belt-drive ceiling fans. These were also similar in design to gear-drive and friction-drive fans; however, instead of a rubber friction wheel or toothed gear, a small rubber belt linked the motor to the flywheel. The most notable internal belt-drive ceiling fan was a model sold by Toastmaster.

• Belt-driven ceiling fans. As stated earlier in this article, the first ceiling fans used a water-powered system of belts to turn the blades of fan units (which consisted of nothing more than blades mounted on a flywheel). For period-themed decor, a few companies (notably Fanimation and Woolen Mill) have created reproduction belt-drive fan systems. The reproduction systems feature an electric motor as the driving force, in place of the water-powered motor.
• DC ceiling fans. These fans use a brushless DC motor that offer much better efficiency than traditional fans driven with AC motors. They usually are quieter than AC motor fans due to the fact they are commutated electronically and use permanent magnet rotors. Among many advantages these fans offer some are higher efficiency, lower noise level, less rotor heat, integration of remote control and other convenience technologies etc. The only drawbacks are the high cost and the presence of complex electronics which may be more likely to fail, making them not ideal for commercial installs containing a large number of fans. However, with the advent of new technologies and better quality control techniques, the latter is becoming less of a concern.
• Hugger ceiling fans (also known as "flush mount" or "low profile" ceiling fans) have no downrod or canopy like a traditional mount fan, and the motor housing is mounted directly to the mount. Hugger style fans generally have spinner motors, and use a special mounting bracket that holds the motor assembly and the motor housing. They are typically used in rooms with low ceilings. A disadvantage to this design it that since the blades are mounted so close to the ceiling, the air movement is greatly reduced.
• Bladeless ceiling fans. This type was introduced in 2012 by Exhale fans and uses a bladeless turbine to push air outwards from the fan, which is also the case of regular ceiling fans on updraft mode. These feature a brushless DC motor instead of a normal direct drive motor.
• High-volume low-speed fans (HVLS fans) are large-diameter ceiling fans intended for large spaces such as warehouses and gymnasiums. These fans generally spin at a low speed and they use airfoil-style blades for optimized air movement. One of the most popular manufactures of HVLS fans is Big Ass Fans.
• Synchronous motor mini ceiling fans- these are relatively small in size and are made almost completely out of plastic.
• Punkah style ceiling fans. These fans are based on the earliest form of a fan, that was developed in India which was originally cut from an Indian palmyra leaf. A punkah fan moves slowly in a pendular manner with a rather large blade and is nowadays electrically powered using a belt-driven system. In comparison to a rotating fan it creates a gentle breeze rather than an airflow.

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Safety concerns with installation

A typical ceiling fan weighs between 15 and 50 pounds when fully assembled. While many junction boxes can support that weight while the fan is hanging still, a fan in operation exerts many additional stresses--notably torsion--on the object from which it is hung; this can cause an improper junction box to fail. For this reason, in the United States the National Electric Code (document NFPA 70, Article 314) states that ceiling fans must be supported by an electrical junction box listed for that use. It is a common mistake for homeowners to replace a light fixture with a ceiling fan without upgrading to a proper junction box.

Low-hanging fans/danger to limbs

Another concern with installing a ceiling fan relates to the height of the blades relative to the floor. Building codes throughout the United States prohibit residential ceiling fans from being mounted with the blades closer than seven feet from the floor; this sometimes proves, however, to not be high enough. If a ceiling fan is turned on and a person fully extends his or her arms into the air, as sometimes happens during normal tasks such as stretching or changing bedsheets, it is possible for the blades to strike their hands, potentially causing injury. Also, if one is carrying a long and awkward object, one end may inadvertently enter the path of rotation of a ceiling fan's blades, which can cause damage to the fan. Building codes throughout the United States also prohibit industrial ceiling fans from being mounted with the blades closer than 10 feet from the floor for these reasons.

MythBusters: "Killer Ceiling Fan"

In 2004, MythBusters tested the idea that a ceiling fan is capable of decapitation if an individual was to stick his or her neck into a running fan. Two versions of the myth were tested, with the first being the "jumping kid", involving a kid jumping up and down on a bed, jumping too high and entering the fan from below and the second being the "lover's leap", involving a husband dressed in a costume, leaping towards his wife in bed and entering the fan side-on. Kari Byron, Tory Belleci and Scottie Chapman took the lead on the investigation, though original MythBusters Jamie Hyneman and Adam Savage also assisted.

First, Kari and Scottie purchased a regular household fan and also an industrial fan, which has metal blades as opposed to wood and a more powerful motor. They and Tory then fashioned their human analogs - ballistic gel busts of Adam with actual human craniums, pig spines to approximate human spines, and latex arteries filled with fake blood - and then constructed rigs for both scenarios.

They busted the myth in both scenarios with both household and industrial fans, as tests proved that residential ceiling fans are, apparently by design, largely incapable of causing more than minor injury, having low-torque motors that stop quickly when blocked and blades composed of light materials that tend to break easily if impacted at speed (the household fan test of the "lover's leap" scenario actually broke the fan blades.) They did find that industrial fans, with their steel blades and higher speeds, proved capable of causing injury and laceration - building codes require industrial fans to be mounted with blades 10 feet above the floor, and the industrial fan test of the "lover's leap" scenario produced a lethal injury where the fan sliced through the jugular and into the vertebrae - but still lost energy rapidly once blocked and were unable to decapitate the test dummy. As a finale, Scottie, Tory and Kari created an even more dangerous fan with a lawn mower engine as the fan motor and razor sharp blades made from sheet metal in an attempt to duplicate the result, and even it was unable to achieve decapitation, but it caused lethal and horrifying injuries that compelled Adam to put it into the "MythBusters Hall of Fame."

Wobble

Wobbling is caused by the weight of fan blades being out of balance with each other. This can happen due to a variety of factors, including blades being warped, blade irons being bent, blades or blade irons not being screwed on straight, or blades being different weights or shapes or sizes. (Minute differences matter.) Also, if all the blades do not exert an equal force on the air (because they have different angles, for instance), the vertical reaction forces can cause wobbling. Wobbling is not affected by the way in which the fan is mounted or the mounting surface.

Contrary to popular misconception, wobbling alone will not cause a ceiling fan to fall. Ceiling fans are secured by clevis pins locked with either split pins or R-clips, so wobbling won't have an effect on the fan's security, unless of course, the pins/clips were not secured. To date, there are no reports of a fan wobbling itself off the ceiling and falling. However, a severe wobble can cause light fixture shades or covers to gradually loosen over time and potentially fall, posing a risk of injury to anyone under the fan, and also from any resulting broken glass. It is also worth mentioning that when the MythBusters were designing a fan with the goal of chopping off someone's head, Scottie used an edge finder to find the exact center of their blades with the aim of eliminating potentially very dangerous wobbling of their steel blades. It is important that, when installing the fan, the installer closely follows the manufacturer's instructions with regard to using proper mounting screws. It is also important that all screws (especially the set screws which hold twist-on downrods in place) be tight, and any ceiling fan light fixtures are properly assembled with their shades and covers securely attached.

Source of the article : Wikipedia