Ceiling Fan

A ceiling fan is a device suspended from the ceiling of a room that employs hub-mounted rotating paddles to circulate air in order to produce a cooling or destratification effect.

Generic-style ceiling fan from the early 1980s

 

Uses

Most ceiling fans can be used in two different ways; that is, most fans have a mechanism, commonly an electrical switch, for reversing the direction in which the blades rotate.

In summer, when the fan’s direction of rotation is set so that air is blown downward (typically counter-clockwise, when standing under the fan and looking upwards), the breeze created by a ceiling fan speeds the evaporation of sweat on human skin, which is experienced as a cooling effect.

In winter, buildings in colder climates are usually heated. Air naturally stratifies—that is, warmer air rises to the ceiling while cooler air sinks to the floor. A ceiling fan, with its direction of rotation set so that air is drawn upward (typically clockwise), takes cool air from lower levels in the room and pushes it upward towards the ceiling. The warm air, which had naturally risen to the ceiling, is forced out of the way of the incoming cool air; it travels along the ceiling and down the walls, to lower levels where people in the room can feel it. This reverse rotation has the added advantages of not creating the wind-chill effect of the summer operation scheme, and of heating the air slightly by forcing it along the entire surface area of the ceiling, which is typically hot due to risen hot air trapped on the other side in the attic.

Even though most ceiling fans can be mounted to all types of ceilings, not all can be mounted to angled or cathedral ceilings without an added bracket or down-rod (a metal pipe used to suspend the fan from the ceiling).

Parts of a Ceiling Fan

The key components of a ceiling fan are

• An electric motor.
• Two to six paddles (called blades). These are usually made of wood, MDF, metal, or plastic and are mounted under, on top of, or on the side of the motor. The majority of residential ceiling fans have either four or five blades, while most industrial ceiling fans have three. However, a few specialized art fans (fans made more for decorative appearance than functionality) have other numbers of blades, such as one, or eight or more.
• Metal arms, called blade irons (alternately blade brackets, blade arms, blade holders, or flanges), which connect the blades to the motor.
• A mechanism for mounting the fan to the ceiling.
  • Some fans mount using a ball-and-socket system. With this system, there is a metal or plastic hemisphere mounted on the end of the down-rod; this hemisphere rests in a ceiling-mounted metal bracket and allows the fan to move freely. Some companies have come up with slight modifications of this design.
  • Some fans mount using a J-hook (also known as a claw-hook) system. In this system, a metal hook (which comes in a variety of configurations) secures to a ceiling-mounted metal bolt (again, available in a variety of configurations). Usually, there is a rubber bushing inserted between the hook and the bolt as a noise-reduction agent.
  • Some fans can be mounted using a low-ceiling adapter, a special kit that can be purchased from the fan’s manufacturer. The low-ceiling adaptor eliminates the need for a down-rod, 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 down-rod (a metal pipe used to suspend the fan from the ceiling). Down-rods come in many lengths.
• A decorative encasement for the motor (known as the motor housing).
• A switch housing (also known as a switch cup), 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 that allow light to shine though.

Configurations

• Commercial or industrial ceiling fans are usually used in offices, factories, or industries. Commercial ceiling fans are designed to be cost effective and can save more than 75% in energy, which is always welcome in businesses. The industrial or commercial ceiling fans only use three blades plus a high-speed motor to function. To use more blades would strain the motor and use up more electricity. Industrial fans can be purchased with ultra quiet motors. These energy efficient ceiling fans push massive amounts of air compared to traditional ceiling fans. In summer they keep the air circulating, and in winter they push warm air from the ceiling to the floor.

• A hugger or low-profile ceiling fan is installed as close as possible to the surface of the ceiling without the ceiling fan blades scraping it. Hugger fans are usually installed in rooms that have low ceilings; they cannot be used in rooms with vaulted ceilings. In cold climates, a ceiling fan may disperse heat to warm up the room as well as 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 may be used in covered locations but outside the house proper, such as in a porch exposed to the garden. The outdoor ceiling fan should never be placed where the elements (especially water) can reach it and its motor. An outdoor ceiling fan should be covered with a rust-proof finish and should have non-warp blades. Outdoor fans are made of materials that can withstand cold, heat, and 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%) and have lower price tags. There are also Energy Star ceiling fans cooling other types of structures besides home such as warehouses, offices, businesses, and schools. Energy Star ceiling fans are available in home repair stores and furniture stores and can also be ordered online.

Bases for Comparison

There are several factors that determine a fan’s efficacy and efficiency. Each of these factors can be used as a basis for comparison when deciding what type of fan to purchase.

A fan’s efficacy (in other words, its ability to generate airflow) is measured by its CFM (cubic feet of air moved per minute) rating. The following factors all have an effect on a fan’s CFM rating:

• Length of the fan’s blades. The longer a fan’s blades are, the larger the percentage of a room’s air volume the fan will have a relevant impact upon. This factor is of greater importance in large rooms. The majority of ceiling fans come in one of three sizes (sweep diameter): 36 in., 42 in., or 52 in.
• Total surface area of the fan’s blades. The greater a blade’s surface area, the more air it is able to move. However, there can be "too much" surface area (refer to Blade surface area to air-feed ratio below).
• Pitch of the fan’s blades. The angle at which the fan’s blades are tilted relative to the X-axis is referred to as the blade pitch. The steeper (greater) the pitch, the greater the airflow. Since increased pitch also means increased drag, only fans with well-made motors can support steep pitches. Cheaply made fans typically have a pitch between 9 and 13 degrees. A pitch of 15 degrees and upwards is considered very good, with numbers in the 20s being the highest.
• Speed of rotation. The speed at which a fan rotates, measured in RPM (revolutions per minute), directly correlates to the amount of air moved. Faster rotation equals greater air flow.
• Blade surface area to air-feed ratio. In general, more blade surface area means greater airflow. However, if there is too much blade surface area, there will not be adequate space between the blades for air to be drawn through. Fans that have an unusually large blade surface area, such as fans with decorative palm-leaf-style blades or many fans with six blades, do not have adequate space between the blades for an unrestricted amount of air to be drawn through. The result is reduced air flow. Contrary to popular belief, more blades typically does not equal more airflow. Most four-bladed fans move more air than comparable five-bladed fans spinning at the same speed; this is indeed noticeable on five-bladed fans which have an option to install only four of the blades.
• Height of the fan relative to the ceiling. If a fan is too close to the ceiling, the air flow is restricted; that is, the fan will not be able to draw as much air through its blades as it has the potential to do. For this reason, hugger fans (those which mount directly to the ceiling without the use of a down-rod) are inherently disadvantaged. The distance that a fan should be mounted from the ceiling is directly correlated with its air-moving potential; no fan should be mounted with its blades less than 24 in. away from the ceiling. However, that figure is often far greater with industrial fans. Unfortunately,mounting the fan more than 24 in. from the ceiling is often impossible in household situations, since a minimum ceiling height of nine feet would be required to meet most safety regulations (safety codes typically require that the blades be mounted a minimum of seven feet from the floor).

In addition to all of the aforementioned factors, there are certain other factors that have an effect on a fan’s perceived efficacy (how efficacious an observer experiences a fan to be):

Note that this fan’s blades are tilted relative to the Z-axis; that is, they are tilted upwards.

• Height of the fan relative to the observer. The closer the fan is to the observer, the more air movement the observer will feel. A fan mounted close to the ceiling in a high-ceilinged room will have a lower perceived efficacy than if it were mounted closer to the ground.
• Tilt of the fan’s blades relative to the Z-axis. A few fan manufacturers, notably FASCO, constructed their fans such that the blades had an "up-tilt"; that is, they were tilted relative to the Z-axis. While this increased the area of the room over which the fan had a direct effect, thereby increasing the efficacy perceived by persons standing at the edges of the room, it decreased the airflow concentrated immediately under the fan, thereby reducing the efficacy perceived by anyone standing or sitting directly underneath it. Some industrial ceiling fans have the tips of the blades bent to the Z-axis so that the area of the room over which the fan has a direct effect will be greater. The perceived efficacy directly under one of these fans is not affected as much as if the entire blade were tilted relative to the Z-axis.
• Humidity of the room. Since a fan creates its cooling effect by speeding the evaporation of moisture (both sweat and ambient humidity) on human skin, its perceived efficacy is directly correlated with the amount of humidity (moisture) in the room. In dry environments, such as desert climates, a fan has a lesser perceived efficacy than in humid environments.

In terms of efficiency (in other words, air flow generated versus energy input), the basis for comparison is to divide the fan’s CFM rating by its input wattage. So, if the fan moves 6630 CFM on its highest speed, and uses 85 watts to do so, its energy efficiency is 78. A consumer can apply that same equation to several candidate fans to objectively compare their energy efficiency.

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:

A cast-iron ceiling fan made by Hunter, dating from the early 1980s. This model is called the "Original."

• 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 as the "Classic Original," with several spin-off models). The Original employed a shaded-pole motor from its inception until the late 1980s, 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 overseas; the motor, though still oil-lubricated, was switched to a skeletal design, as discussed below.

A close-up of the dropped flywheel on a FASCO ceiling fan

• 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. 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 squirrel-cage 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 "K55" and "K63" motors, and Casablanca with the "XLP-2000." One of the earliest stack-motor fans was the Emerson "Universal,", a utilitarian fan with a dropped flywheel and blades made of fiberglass or plastic. This fan was produced from 1976 through 1983 and, while targeted at commercial settings, also found great success in residential settings. Another stack-motor fan, one without the dropped flywheel, is the Casablanca "Delta." While this motor is not nearly as widely used as it was in the 1970s and 1980s, it can still be found in certain high-end Casablanca and Emerson fans, as well as in the Marley "Gillespie." One disadvantage of this type of fan is that the flywheel, if it is made from rubber, will degrade over time and eventually fail.

• Direct-drive ceiling fans employ a motor with a stationary inner core with a shell 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 (which debuted 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 type accounts for most industrial fans (though such fans sometimes have more moderate-quality motors) and some inexpensive residential fans (particularly those made overseas).
  • Spinner-motor fans, sometimes confusingly (and 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, including nearly all fans made overseas.

• Skeletal motors, which are a high-quality subset of direct-drive motors, can be found on some nicer 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 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 employed a low-torque motor that was 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), 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.

• 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.

• Belt-driven ceiling fans. The earliest 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) have created reproduction belt-driven fan systems. The reproduction systems feature an electric motor as the driving force, in place of the water-powered motor.

Safety Concerns with Installation

A typical ceiling fan weighs between 15 and 35 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.

Another concern with installing a ceiling fan relates to the height of the blades relative to the floor. US law states that no fan can be mounted with its blades closer than seven feet from the floor; this often proves, however, to not be high enough. If a person fully extends his or her arms into the air—as sometimes happens during normal tasks such as stretching, changing bedsheets, or recreation—he or she may become seriously injured if there is an operating ceiling fan mounted too close. Also, if one is carrying a ladder or some other long and awkward object, one end may inadvertently enter the path of rotation of a ceiling fan’s blades. Such a collision can be very dangerous if the fan is operating at the time, and can cause damage to the fan regardless.

Wobbling

Wobbling is not created or influenced by the ceiling on which the fan is mounted, by the way the fan is mounted, or by any other factors along those lines. Rather, the one and only cause of wobbling is fan blades being out of weight-alignment 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, blades being different weights or shapes or sizes (minute differences matter), and so on.