Ceiling fans
Which are the components and performance metrics of ceiling fans?
Last updated
Which are the components and performance metrics of ceiling fans?
Last updated
There are multiple fan types available in the market, but ceiling fans outweigh their benefits over the other fan types in terms of air circulation effectiveness and low energy consumption, especially for serving multiple occupants within the same space. In addition, installation and operation of ceiling fans are specific to building design and different from other portable fan options. Therefore, this guide highlights a separate section for ceiling fans, while other fan choices (i.e., other air movement devices) will be clustered in another section.
The following sections describe the different types of ceiling fans, and the features that differentiate ceiling fan models.
A part of the "Uniform Test Method for Measuring the Energy Consumption of Ceiling Fans" from the US Department of Energy (DOE) defines a variety of ceiling fan types. This guide focuses on several of them defined below:
Standard ceiling fan: any ceiling fan with a diameter greater than 45 cm [18 in] but no more than 2.1 m [7 ft], and with the lowest point of the fan blades more than 25 cm [10 in] below the ceiling. A standard ceiling fan does not exceed the limits outlined in Table 1 below.
Large-diameter ceiling fan: any ceiling fan that is greater than 2.1 m [7 ft] in diameter. These are often also known as High Volume Low Speed (HVLS) fans.
Small-diameter ceiling fan: any ceiling fan that is more than 46 cm [18 in] in diameter but less than or equal to 2.1 m [7 ft] in diameter, and with an airflow of at least 0.87 m³/s [1840 CFM] and a rotational speed of more than 1.5 Hz [90 rpm] at its highest speed.
High-speed small-diameter ceiling fan: any small-diameter ceiling fan that has a blade thickness of less than 3.2 mm [12.6 in] at the edge or a maximum tip speed greater than the applicable limit specified in Table 1 below.
Low-speed small-diameter ceiling fan: any small-diameter ceiling fan that has a blade thickness greater than or equal to 3.2 mm [12.6 in] at the edge and a maximum tip speed less than or equal to the applicable limit specified in Table 1 below. (“Standard ceiling fans”, defined above, are a type of low-speed small-diameter ceiling fan).
Hugger ceiling fan: any low-speed small-diameter ceiling fan for which the lowest point on the fan blades is less than or equal to 25 cm [10 in] from the ceiling.
Very-small-diameter ceiling fan: any ceiling fan with one or more fan heads, each of which has a blade span of 46 cm [18 in] or less, and with an airflow of at least 0.87 m³/s [1840 CFM] and a rotational speed of more than 1.5 Hz [90 rpm] at its highest speed.
Highly decorative ceiling fan: any ceiling fan with a maximum rotational speed of 1.5 Hz [90 rpm] and less than 0.87 m³/s [1840 CFM] airflow at high speed
Note that while these DOE definitions include a variety of sub-categories for small-diameter fans, any fan larger than 2.1 m [7 ft] in diameter is simply a “large-diameter” fan, with no further differentiation.
Table 1. Ceiling Fan Blade and Tip Speed Criteria (Adapted from DOE Definitions).
| Airflow Direction | Thickness (t) of edges of blades | Thickness (t) of edges of blades | Tip speed threshold | Tip speed threshold |
|---|---|---|---|---|
The DOE also defines a variety of other specialty ceiling fan types (including belt-driven ceiling fans, centrifugal ceiling fans, multi-head ceiling fans, and oscillating ceiling fans), but those specialty types are not the subject of this guide. This guide primarily focusses on two main ceiling fan types, defined above as “standard ceiling fans” and “large-diameter ceiling fans”. However, much of the discussion in this guide will also be relevant to the other small-diameter ceiling fan types beyond the “standard” definition, and there is significant overlap between many of the small-diameter ceiling fan sub-categories. Note, for example, that “standard ceiling fans” are a type of low-speed small-diameter ceiling fan, and “hugger ceiling fans” are essentially equivalent to standard ceiling fans but with fan blades mounted closer to the ceiling (despite the negative effect on efficiency) for suitability in spaces with lower ceiling heights.
In general, a larger diameter fan blade can move a larger volume of air than a smaller diameter fan blade. As fan diameter increases, rotational speed is typically limited to prevent excessive noise from the fan blades, especially near the blade tip. Additionally, where fans can be mounted at blade heights below 10 ft (i.e., almost all standard fans), rotational speed must be limited to meet safety criteria (see UL 507: Standard for electric fan) for the maximum speed of the blade tips. Large-diameter ceiling fans are sometimes referred to as “high volume low speed” or HVLS fans. Because the design and shape of the fan blades can also have a significant impact on airflow, as described in more detail below, the HVLS terminology is typically used to describe large ceiling fans that are designed to prioritize performance in large commercial and industrial spaces. For example, some large-diameter ceiling fans include “winglets” or blade tip fences to maximize airflow and minimize noise, which is a less common problem in standard fans as the blade tip speed is already constrained for safety reasons.
Though standard ceiling fans are more applied in residential applications, they are equally effective for comfort cooling in most non-residential applications (including offices, classrooms, gyms, hospitality, etc.) where they can be positioned near the occupants. Large-diameter ceiling fans require higher ceilings (typically at least 3.3 m [11 ft]) and larger spaces free from obstructions to accommodate their increased diameter. As a result, large-diameter ceiling fans are most often found in non-residential commercial and industrial applications.
Although the fan type definitions from the DOE focus on fan diameter, in the case of specific fan products there is some overlap in terms of applications and fan styles. Some large-diameter fans are available in styles that are more frequently associated with standard fans, and some manufacturers have HVLS fan models in diameters less than 2.1 m [7 ft]. Additionally, there are some large-diameter fans that have a relatively low maximum rotational speed and thus, meet blade tip speed and thickness requirements for mounting below 3 m [10 ft], though these also have a relatively low maximum airflow.
Blade shape, number of blades, and blade pitch are important factors in increasing energy efficiency while maximizing airflow through the fan blades. There are two main types of blades shapes shown in Figure 8 below. Blade shapes have evolved over time from flat to airfoil-style blades to become more energy efficient and maximize air movement. As the name implies, flat ceiling fan blades are flat panels mounted at a fixed angle, whereas airfoil blades are like airplane wings in section. Like the cross-section of an aircraft wing, the curvature of the airfoil blades helps increase airflow through the ceiling fan, minimizing air turbulence at the trailing edge of the blade common to flat blades. Airfoil-style blades are thus typically more efficient and quieter than flat blades. However, flat blades are cheaper to manufacture. Note that flat blades will perform equally whether the fan is operating in the forwards (blowing down) or reverse (blowing upwards) direction. In contrast, airfoil blades will not operate as efficiently in reverse, and will typically have a lower airflow when doing so. Some fan models have blades that can be manually attached in inverted position or can mechanically invert the blade while it is attached to the fan, which allows for improved efficiency when operating in reverse.
The number of blades is an important factor in increasing airflow of ceiling fans. Nevertheless, the increased weight and drag due to the blades can cause a loss in energy efficiency. Standard fans typically have between 3 and 5 blades, though some models have as few as 2 blades or up to 6 blades. Large-diameter fans typically have 6 or 8 blades, with some models having as few as 3 blades.
Similarly, increasing the blade’s angle may also increase airflow at the cost of energy efficiency. Academic modeling studies have found the optimal blade angle to be 8-10 ° for residential fans. Manufacturers recommend 12-15 °. Some airfoil-style blades also vary the blade angle over the length of the fan blade, with steeper angles toward the center of the fan to maximize airflow for the low blade speed in this region and reducing to shallower angles toward the tips where the blade speed is high to limit drag and maximize energy efficiency.
There are three main types of motors used in ceiling fans: AC induction, permanent magnet DC (PMDC), and brushless direct current (DC) motors. Generally, there are very large percentage efficiency savings when changing from AC to DC motors for small fans, and far less of an effect for large diameter fans. AC induction works with electromagnets outside the motor that creates a rotating magnetic field causing motor rotation through induction. The benefits are that it provides constant and even airflow and it is cheaper than DC motors. PMDC has magnets located on the motor creating a stationary magnetic field. A segmented commutator rotates within the magnetic field creating a mechanical switching of current direction. The benefit is being more energy efficient than AC motors and providing constant force over a wider range of speeds than AC motors. Brushless DC work with permanent magnets rotated in motor creating a rotating magnetic field. The current direction in the stator is switched in relation to the magnetic field to create rotation. This is the most energy efficient motor types (for small motors on small diameter fans, a DC motor often will use 70 % less energy than an AC motor), most quiet, and has a longer service life than PMDC motors, with the same benefit of enabling a wider range of air speed.
Fans may also be either direct drive or gear driven. Almost all small-diameter fans are direct drive, but large-diameter ceiling fans may either be direct-drive or gear-driven. Direct-drive fans are quieter than gear-driven fans, which have a more refined appearance, and reduced operating cost. However, direct-drive fans do provide less airflow and it may be harder to replace the motors. Due to this, direct-drive fans are typically used in situations where sound level and aesthetics are a concern, and less airflow is needed.
On the other hand, gear-driven fans allow for higher motor power and are often used in situations where maximizing airflow is a priority over sound levels or aesthetics. This is well suited for industrial settings where ceilings are high and there is little or no air conditioning.
Several factors determine a ceiling fan’s performance, as well as its suitability to a given application. Some of the most critical factors are described in the following sections.
Ceiling fans are available in a wide range of diameters, from very small fans approximately 45 cm [18 in] in diameter to very large fans up to 7m [24 ft] in diameter. Determining the appropriate fan diameter depends largely on the dimensions of the space and the application, as discussed in more detail later in this guide. The California Energy Commission maintains the Modernized Appliance Efficiency Database System (MAEDbS), which contains a large dataset of information on ceiling fans as well as many other types of appliances. For context, this dataset shows that most fan models on the market today are between 1.2 – 1.5 m [4 – 5 ft] in diameter, and presumably therefore aimed at the residential market, as illustrated in Figure 9, below.
All other factors being equal, a larger diameter fan will produce greater airflow through the fan than a smaller diameter fan at the same rotational speed. Figure 10 shows a range of example fans of varying diameters and the range of possible airflows and rotational speeds at which those fans can operate. In general, higher airflow through the fan generally results in higher average air speeds in the space. Additionally, larger fan diameters increase the uniformity of air speeds throughout a space. Lastly, larger diameter fans increase the depth of the boundary layer of air moving along the floor in the spreading zone outside the fan blades. This figure also highlights the differences between fan models even if they have the same diameter. Comparing the Type G and Type F fans, of equal diameter (2.4 m [8 ft]), it shows the range of performance varies by fan type. The Type G fan has a higher maximum airflow, a lower minimum airflow, and a higher rotational speed for any particular airflow.
For any particular fan, airflow is linear with rotational speed, as Figure 10 also shows. Additionally, the air speed at any point in the space is also directly linear with fan rotational speed. So, if a point in the room measures 0.5 m/s [100 fpm] when the fan is rotating at 1.3 Hz [80 rpm], it will measure approximately 0.25 m/s [50 fpm] at 0.7 Hz [40 rpm]. This relationship begins to break down at very low air speed, very low rotational speeds, or where the fan blade height is unusually far from the floor (e.g., > 3 m [10 ft]).
The power consumed by a fan increases in proportion to the cube of its rotational speed, while the airflow generated by the fan increases linearly with its rotational speed. Thus, fan efficacy - or the airflow per unit power consumed - decreases as fan speed increases. However, in many fan models, motor efficiency is poor at lower speeds, partially counteracting this effect. In the MAEDbS dataset, the typical (median) fan efficacy at the lowest operating speed of each fan is 0.08 m³/s·W [165 CFM/W], while it is 0.04 m³/s·W [79 CFM/W] at highest operating speed. Note that the only way to make a direct energy performance comparison between one fan and another is to compare it under the same conditions - the same diameter and the same power (or the same airflow). This is because fans with lower-rated maximum airflows will have a better-rated efficacy even if they consume more power to provide the same airflow. Note that the US Department of Energy and ENERGY STAR criteria – and the metric that shows up on the Energy Guide label - calculates the ceiling fan airflow efficacy using an average of the metric at different operating speeds, weighted according to the amount of time the fan is expected to operate at those speeds, including a standby power loss. However, this does not account for the maximum and minimum airflows between fans of the same diameter, so it can be misleading. As before, fans with lower maximum airflow will generally perform better in this efficacy metric. Figure 11 highlights the issue, where three fans have the same 0.11 m³/s·W [234 CFM/W] efficacy, but there is a clear difference in performance between the fans due to the different range of airflows provided. The fan represented by the left most curve (least efficient, lowest maximum airflow) is rated as having the same overall efficacy as the fan represented by the right most curve (most efficient, highest maximum airflow).
Meanwhile, the ceiling fan energy index (CFEI), a ratio of reference fan power input to actual fan power input, is a more reliable alternative in reflecting the above blind spot. It helps to make inefficient fans less likely to comply with slower speeds and to remove the unintentional barrier to compliance for high-performing high-utility fans by comparing fans to a standardized baseline. Taken the same example in Figure 11, CFEI at high fan speed for the left most and right most curve is, respectively, 0.63 (less efficient) and 1.72 (more efficient). See section “Ceiling fans testing regulations” for more information.
Fans that can turn down to a low rotational speed and maintain good motor efficiency at that speed can operate very efficiently under those conditions. There are several fans in the market with an efficacy of over 0.47 m³/s·W [1000 CFM/W] at their lowest operating speed. Other fans typically have a relatively high minimum speed, and often also have poor motor efficiency at that speed, and these fans benefit less from speed reduction. Generally, the ability of a fan to operate efficiently at lower speed improves as the diameter increases, as Figure 12 demonstrates.
However, there is considerable variation in performance between models of fans with the same diameter, as Figure 13 shows. This also demonstrates that there is a wide range of turndown ratios (minimum speed divided by maximum speed) among different fan models at the same diameter. Some fans can operate at or below 20% of their maximum rotational speed, while others cannot run below 50% of their maximum rotational speed. This is also apparent in the MAEDbS data, as Figure 14 shows.
Drawing data again from the CEC’s MAEDbS system, Figure 15 presents random samples of the fans available in the database. This gives a perspective of the range of fan diameters and associated range of fan airflows available on the market today. The test methods for rating the airflow of these fans are federally regulated under 10 CFR 430 Appendix U. For standard fans, the rating is determined by a modified Energy Star method, which infers airflow from an anemometer traverse below the fan. For large diameter fans (above 7ft), the rating is determined by the AMCA 230-15 test method, which infers airflow from a load cell measurement of fan.
All fans sold in the USA are required to be reversible, and thus, fans can run in either direction – forwards, blowing downwards towards the floor, or in reverse, blowing upwards towards the ceiling. Many standard ceiling fans will have a switch on either the wall switch, remote control, or on the motor housing to change the direction between downwards and upwards. For some models this functionality will be provided in the control system or smartphone app. Most applications are for fans blowing downwards, as this is by far the most common and efficient way of creating air movement in the occupied space. Reversing a fan so that it blows upwards against the ceiling requires that the space containing the fan (or fans) is bounded by a ceiling and walls on all sides. This creates a similar recirculation cell as blowing the fan downwards, but it avoids creating a region of high air speeds directly under the fan. Running fans in reverse has the effect of creating a much lower, but much more uniform air speed distribution in the space, which can be desirable in some applications.
One application of running fans in reverse is to mix air the room when elevated air speed in the occupied zone is not desirable. One example is destratifying spaces in the heating season. Many fans have a relatively high minimum rotational speed and if these fans run in the downwards direction, the resulting air speeds may cause a draft on the occupants directly below the fan. This can be remedied by running the fan in reverse. Note here that there are also fans that have a very low minimum speed, allowing them to run forwards without creating a draft on the occupants, while still effectively de-stratifying the space. This uses less power to destratify than a fan with a higher minimum speed running in reverse. Another application of running fans in reverse is when elevated air speed in the region directly under the fan is perceived as excessive for some reason, such as causing paper to blow off a desk.
The ratio of airflow through a fan in the upwards vs. downwards direction depends on the fan type and associated blade geometry. Some fans have highly optimized blade designs that blow downwards efficiently. Here, the blade geometry is not symmetrical when the fan reverses direction, and these do not generate as much airflow at the same rotational speed and power when operated in reverse. Other fans, such as those with a less efficient but symmetrical blade geometry (e.g., flat blades) or those whose blades can be inverted and re-attached to the fan (making the blade geometry symmetrical in reverse), will generate approximately the same airflow operating in reverse.
For context, based on full scale laboratory testing the area weighted average air speed for seated and standing occupants with a fan blowing upwards ranged from 30 to 70% that of the same fan blowing downwards at the same speed in the same room. In cases where the blade geometry is symmetrical (flat blades, or inverted blades), the area weighted average air speed was approximately 60-70% that of the downwards case. Obstructions in the flow from the fan (e.g., furniture, ceiling obstructions, etc.) will likely have a significant effect on these percentages.
The fan air speed is calculated by dividing the rated airflow of the fan by its diameter. It represents the average air speed that passes through the circle swept by the fan blades. Thus, as with rated airflow, fan air speed varies linearly with fan rotational speed, in other words the airflow rate of a ceiling fan can be scaled (up or down) by its rotational speed. Fan air speed is a useful metric as it is more directly representative of the air speeds that will occur in the space. For example, the maximum air speed at any location and height in the room will typically be within 1.3 to 1.5 times the fan air speed, and it will occur below the fan blade tip, slightly inside the fan blade diameter. That applies regardless of fan diameter. Unlike fan rotational speed, airflow, or power consumption, the concept of fan air speed is also very useful as it allows designers to directly compare fans with different diameters to one other. Figure 16 presents an example from MAEDbs that fans with higher maximum fan air speeds will yield higher maximum air speeds in the room regardless of fan diameter. By using the fan air speed as a metric instead of the rated airflow (see Figure 15), one can directly compare fans to each other even if the diameter differs substantially. This is useful in cases when the design target is the maximum air speed directly underneath the fan.
Most standard fans typically have several fixed fan speed levels. Though some of these fans have a wide range of speed levels (6 or more), most fans have just 3 (see Figure 17). These are typically standard fans with AC motors, whereas DC motor fans tend to have more speed levels. Large diameter fans are typically variable speed regardless of motor type.
The minimum rotational speed on fans with just 3 speed levels is typically still quite high, and often the minimum speed may generate 0.75 m/s [150 fpm] seated average directly under the fan, equivalent to over 2.8 °C [5 °F] cooling effect. Having a high minimum speed can be problematic in some applications, such where there are occupants located directly under the fans for extended periods of time (e.g., an office) or when the fan is used to destratify a space in heating mode. The reason is that the minimum speed may generate too much of a cooling effect for the occupants when temperatures are mild or cool, and they cannot reduce the speed further without switching the fan off. In contrast, a high minimum speed is less of a concern in transiently occupied spaces, spaces where occupants can move freely around. Overall, in most applications, it is desirable to have more levels of speed control, particularly a minimum level that is slow enough that it generates low air speeds directly under the fan. A reasonable approximation is that the minimum fan air speed should be below 0.4 m/s [80 fpm], or a 1.7 °C [3 °F] cooling effect at the minimum allowed blade height, depending on the specifics of the application.
The amount of variation of the air speeds in a space is an important design consideration. Figure 18 below shows the measured air speeds in a cross section through a 5.5 x 5.5 m [18 x 18 ft] room with a 1.5 m [5 ft] diameter ceiling fan located at the center of the room. The airflow ‘jet’ from the fan immediately narrows to a slightly smaller diameter than the fan blades. The jet then impinges on the floor, creating a stagnation point, and then spreads radially outwards along the floor. Smaller diameter fans have a relatively shallow spreading zone. For the case shown below, the air speed in the spreading zone is still high along the floor at a distance of one fan diameter from the fan center. However, the air speeds are almost unaffected by the fan at a height of 0.5 to 0.7 m at the same location. In contrast, larger diameter fans have a deeper spreading zone. For fans at or above 3m [10 ft] in diameter, the height of the spreading zone at a distance of one fan diameter from the fan center is approximately the height of an average person. However, large diameter fans have lower air speeds directly under the fan center, near the stagnation point. As Figure 19 shows, the larger the ratio of fan diameter to room size is, the more uniform the distribution of air speeds will be in the room.
For a motor, drive, and controller combination, it may be useful to check the IP (Ingress Protection) Rating of the fan defined by IEC Standard 60529. The IP rating describes how well an electrical enclosure keeps water and solids out. A direct drive or gear-driven fan with a higher IP rating means that the fan is suited to running in harsh environments or conditions, which may be required for the application under consideration.
Similarly, any ceiling fans in outdoor applications must be rated for outdoor use. UL (Underwriters Laboratories) provides “Damp Location” and “Wet Location” ratings for electrical products such as lighting and ceiling fans. Damp rated ceiling fans can be installed in covered locations where they may be exposed to moisture but cannot be directly exposed to water such as rain or a hose. Wet rated ceiling fans can be directly exposed to rain or washed down with a hose.
Controls for ceiling fans run the gamut from basic manual on-off and speed controls, to fully automated onboard controls that are also integrated with the building automation system. In any scenario the design and specification of ceiling fans must address a variety of controls considerations. Will the fans be fully manual or automated? Will occupants have control over the fans, and if so how and where? If the fans are automatically controlled, what will the setpoints or triggers be? How much variation in fan speed is necessary for the application? How will ceiling fan controls interface with the HVAC system? These questions must all be considered when planning controls for ceiling fans.
Control needs and priorities will vary from application to application. The following sections provide guidance through the most common decisions related to controls when designing and specifying ceiling fans.
One of the most important control considerations for implementing ceiling fans is how the occupants will control the fans. Typical user interface options are listed below. Note that it is common for ceiling fan installations to combine several of the control types listed below in a single application.
Pull chain: adjust a fan’s speed or light level by pull chain located on the fan. Typically, each fan will have two chains, one for the light, and one to turn the fan on or off and adjust the fan speed, typically through just 3 speed levels. Typically, only used in residential applications.
Wired wall control: slide controls or knobs on the wall connecting to wiring in order to control fan speed and light levels. Wall controls may be preferable for fans with greater fan speed variability or dimmable lighting.
Wireless IR remote control or detachable wall control: wall control or remotes tuned to create a frequency combination enabling wireless control of fan speed and light levels. Like wired wall controls, wireless controls can support greater fan speed variability and dimmable lighting. Wireless controls eliminate the need for hardwired connections, which can be costly in retrofit scenarios, but they also typically use batteries that will need to replace regularly, and if detachable, they can be lost or misplaced.
Wi-Fi or Bluetooth Connectivity via Phone App or Internet: some fans have smartphone apps or web interfaces that use Bluetooth or Wi-Fi networks to control fan speed, light levels, and other settings. This may be especially advantageous for controlling multiple fans in a space or throughout a building but may be less ideal for spaces where multiple people will need access to fan controls. Additionally, note that many fan models can be retrofit with a controller that adds Wi-Fi or Bluetooth control capabilities.
Building automation system interface: some fans may also be controlled through building automation system interface. This approach may be ideal for applications where access to fan control needs to be limited to building management and maintenance staff, such as assembly and hospitality spaces.
Figure 20 demonstrates some examples of wall mounted control for ceiling fan that are not particularly clear to the user. For example, the controls are not labelled as controlling the ceiling fan and as such are indistinguishable from a dimmable light switch in many cases. It is important to ensure that wall mounted fan controls are clearly visible to the occupant(s), located near the fan they control and near the thermostat in the room, intuitive (e.g., levels increase vertically from off to maximum speed), and clearly differentiated from other controls, like lighting controls.
In addition to the user control interfaces listed above, there are a range of options and strategies for ceiling fan control automation. Listed below are some automation strategies that can be implemented for ceiling fans. As with control interfaces, many of these automation strategies can be used in combination. However, the automation options available for any given application will sometimes depend on the capabilities of the chosen ceiling fan model.
The simplest is the manual control option, where there is no automation and fan control is fully manual based on occupant inputs. The schedule option allows to set when the fans are operating, typically at a fixed speed. For example, if a room is generally only used during weekday business hours, a schedule could be set to automatically turn on each weekday morning and turn off at night. Automation based on occupancy option ensures that a fan only operates when the space is occupied. The fans only provide a cooling sensation if an occupant is there to feel it. This control option can be applied in different ways: by a wall switch “vacancy” or “occupancy” sensing; by integration with building automation system (BAS) occupancy sensors (e.g., via power relay, 0-10 V input or BACnet interface to fan); or on-board occupancy sensor (available in some products). Another option is temperature sensing, which allows fans to be programmed to turn on at certain temperature thresholds, and increase speed with temperature, automating the thermal comfort control in a similar manner to a thermostat for a traditional HVAC system. This option can be applied when manufacturer provided wall controller with built in temperature sensor (or remote temperature probe); by integration with building automation system (BAS) occupancy sensors (e.g., via power relay, 0-10 V input or BACnet interface to fan); or on-board occupancy sensor (available in some products). Learning behaviors and/or preference controls can also be used when ceiling fans are equipped with programming that learns user preferences over time. For example, if a user frequently turns off the fan when the room temperature drops to 23 °C [73 °F] the fan will “learn” this user preference and start to automatically turn off at that temperature.
There is amperage restriction to a wall control unit which limits the number of ceiling fans that can be controlled together at once. For example, a wall control unit with an amperage of 5 amps could only control at most 5 fans at once if the load of one fan is about 1 A. In general, the number of fans that may be in a space at once is limited by the National Electric Code standards. The standard mandates that a circuit breaker does not carry more than 80% of its rated current. This means that for a standard circuit breaker with 15-20 A, the circuit breaker will only allow about 12 fans (80 % of 15). To allow for more fans to be controlled at once, fans are often daisy-chained together. When fans are daisy-chained, a control device controls one master fan, and the rest of the fans are controlled by the master fan by a variable-frequency drive.
When using wireless wall controls or remote controls, each fan that is controlled must have a receiver. Additionally, for each new fan desired to be controlled simultaneously with the existing fans, a new receiver must be purchased. The frequency settings must then be reset for the receiver and remote control to match.
Like many building products, ceiling fan costs can vary widely depending on size, material, motor type, and other characteristics. Standard ceiling fans can range from less than US$100 for basic off-the-shelf models to over US$1,000 for more specialized fans with more decorative features, higher quality materials, and/or automated onboard control systems. In general, fans with DC motors tend to be more expensive than fans with AC motors, but DC motors also tend to be more energy efficient, quieter, and more durable than AC motor fans due to better bearings and build quality. A wide range of high quality, efficient standard fans with DC motors are currently available from US$400 upwards. Large-diameter ceiling fans start at approximately US$3,000 and increase in cost with fan diameter and performance characteristics. There is relatively little difference in performance between DC and AC motors for the larger motor sizes associated with large-diameter fans.
Installation costs can vary widely depending on the fan (assembly time, weight and diameter), the space conditions, and whether the installation is a new construction or a retrofit. Very approximately, it can take a professional anywhere from 30 minutes to 3 hours to assemble and install a single ceiling fan depending on the selected model and site conditions. On the low end of that estimate, the time required to install a ceiling fan is simply the labor cost to assemble the ceiling fan and connect it to an existing junction box. On the other hand, a variety of factors can make ceiling fan installations more complicated, and therefore more expensive. The need for additional structural bracing in spaces with suspended ceilings, the need for additional people to handle and install larger fan models, running new wiring for power and controls in retrofit scenarios, and the need for mechanical lifts for installations in spaces with high ceilings are just a few of the factors that can add complication and cost for ceiling fan installations. In retrofit scenarios, if there is already an electrical box in place, installation costs may be minimal, but if new wiring and junction boxes are needed, the installation is likely to be more complicated and more costly. The variations in installation costs also consider external factors beyond the fan installation, such as long travel times to the demonstration sites (several hours each way), and the size and efficiencies of each of the installation projects (e.g., larger jobs had lower average per fan costs since external factors are averaged over a larger number of fans).
mm
in
m/s
fpm
Downward-Only
4.8 > t ≥ 3.2
3/16 > t ≥ 1/8
16.3
3200
Downward-Only
t ≥ 4.8
t ≥ 3/16
20.3
4000
Reversible
4.8 > t ≥ 3.2
3/16 > t ≥ 1/8
12.2
2400
Reversible
t ≥ 4.8
t ≥ 3/16
16.3
3200
