Ceiling Fan Wind Speed Factor
Published by: Greg Tillotson
Webmaster for Hansen Wholesale
11/23/2010 (Revised 1/31/2015)
Ceiling Fan Wind Speed Factor is a rough calculation of the potential Wind Speed any given ceiling fan produces in the column of air directly beneath it.
The calculation is based on the width of the fan and the CFM (Cubic Feet Per Minute of Airflow), which the EPA currently requires ceiling fan
manufacturers to publish. Wind Speed Factor allows you to compare the actual cooling capability between ceiling fans that are of different sizes and CFMs.
Instructions: Enter the blade span and CFMs of any ceiling fan to calculate it's Wind Speed Factor.
By default, the calculator has the numbers in it for the 60" Emerson Carrera Grand ceiling fan
Here's my theory and reasononing behind my Wind Speed Factor Calculator:
Hypothesis: Ceiling fans push air down in a column of air that is roughly the same width (or diameter) as the ceiling fan.
If you have 2 fans that move the same Cubic Feet per Minute of air (CFM) and one is smaller than the other,
the smaller fan will have more concentrated airflow, which will make you feel cooler if you stand or sit directly beneath it.
The larger moves air over a larger area, so you will NOT feel as cool when you are directly beneath it because the main column of airflow is less intense.
Ceiling fans cool you off by creating a wind-chill effect, which is directly related to wind speed (MPH),
not the amount of air that is moved (which is CFM). All ceiling fan manufactureres are now required to test and publish the amount of airflow
their fans produce in CFM. In my opinion, this is a flawed comparison because CFM does not in and of itself tell you how much cooling efffect a fan produces.
Yes, it is a valid comparison if you have two fans that are exactly the same size, then the one with a higher CFM will produce a higher wind speed.
But what about comparing fans of different sizes. Let's say you are not sure if you would be better off with a 52" fan or a 60" fan. If you just compare the CFM, it is likely that
the 60" fan will be higher. But that does not mean it produces a higher wind speed because the amount of air being moved is measured in a larger area and may be less concentrated.
This is why I divised the Wind Speed Factor Calculator, which provides a means of calculating the airflow intensity,
which I have termed "Wind Speed Factor", giving you the ability to compare different size fans with various CFM.
The Wind Speed Factor is expressed in MPH and is calculated based on the CFM reported by the manufacturer and the diameter of the fan plus 8", which
is the diameter of the cylinder used for testing ceiling fan CFM. These are the basic factors necessary to calculate wind speed in an air column.
There is no scientific testing done to prove or disprove my calculations and I will say openly that the calculation is somewhat flawed as it is based on the
assumption that the column of air generated by a ceiling fan is cylindrical in shape, where in reality, the pattern varies between models and actually spreads out wider the closer you get to the floor.
However, the CFM testing procedure required by the federal government
is the foundation for this flaw because it is performed in a cylinder as opposed to an open area.
This is why I use the term "Wind Speed Factor" rather than "Wind Speed", because it is a factor based on the CFM as reported by the testing procedure rather than
an actual scientific measurement of the wind speed.
So although the actual wind speed may be different, the wind speed factor we are calulating does provides a useful way to compare the actual cooling effect between ceiling fans of differing diameters and CFM.
Fan Size -vs- Wind Speed -vs- CFM
Note: The formula for calculating wind speed was revised on 1/31/2015. The previous formula did not take into account that the testing chamber (cylinder) used to determine the CFM of a fan is 8" in diameter larger than the blade span. The revised formula ads 8" to the fan diameter to account for this. The wind speed results are now slightly lower than previosly stated
"When it comes to ceiling fan size...the largest fan with the highest wind speed that will look fine in the area is the best choice!"
Ceiling fans cool you off by creating a wind-chill effect, the degree of which is determined by the wind speed produced by the fan; the higher the wind speed, the cooler you feel. It is critical to know the following; CFM is not the same as wind speed; the wind chill effect you feel from a ceiling fan is concentrated in the column of air directly beneath the fan blades; the wind chill drops off dramatically just a foot or two outside that area.
Ceiling fan manufacturers are required by the DOE to publish the airflow of each fan in CFM (Cubic Feet per Minute) which is not the same as wind speed. CFM is the volume of air being moved every minute, whereas wind speed how fast the air is moving in MPH (Miles per Hour) or LFM (Linear Feet per Minute), both of which are directly related to the amount of wind chill effect. When you compare two fans that are different sizes yet have the same CFM you will find they produce quite different wind speeds. The smaller fan must move air faster in order to move the same amount of air per minute (CFM) as the larger fan. The airflow generated by the smaller creates more wind chill because it is more concentrated and has a higher wind speed. The larger fan of equal CFM moves air over a larger area so it is less concentrated at a lower wind speed. So when determining what size fan to buy you must consider the amount of space a fan will cover (the diameter of the fan plus a foot or two), the intensity of the airflow directly beneath the fan (the wind speed) balanced with how any particular size fan will look or fit in the space. Ultimately the largest fan with the highest wind speed that will look fine in the area is the best choice for performance.
The required testing method for ceiling fans is not done in a way that translates well to real world applications, so the CFM data can be somewhat deceiving if you do not know how to interpret it.
The current required test procedure (shown left) shows a ceiling fan hanging above a 3 foot tall metal cylinder that is 8 inches wider than the ceiling fan (blade span) and stands 4 feet above the floor. Sensors are located at the bottom of the cylinder to measure the wind speed. The wind speed is then converted into CFM (Cubic Feet per Minute). Although this testing procedure can be valuable for comparing the performance of fans equal in size, it does not emulate a real application inside a home and does not make it easy to compare fans that are different sizes in order to determine the best size fan(s) for any particular application.
Therefore, the best way to compare the actual performance between fans of various sizes is to compare the wind speed. The wind speed of a ceiling fan can be mathematically calculated based on the CFM and Blade Span. Here is a comparison where we performed the calculations between 3 fans of different blade spans and CFMs. The largest fan has the highest CFM yet the smallest fan produces the highest wind speed.
84" Fan with CFM of 10000 produces wind speed of 2.46 MPH (216.62 LFM)
52" Fan with CFM of 6500 produces wind speed of 3.76 MPH (331.04 LFM )
The above example shows how deceiving CFM data can be. Even though the 52" fan moves 35% less air than the 84" fan, the intensity of the breeze that produces a wind-chill effect is over 50% more than that of the larger fan and will make you feel much cooler if you are directly beneath it. So, to cover a larger area, two or more smaller fans with good performance may be a better choice than a single large higher CFM fan.
Ceiling Fan Articles:
Everything you need to know about ceiling fans and more. If you have a question about ceiling fans that you cannot find in these resources give us a call at: 1-800-201-1193 or send an email to our webmaster: firstname.lastname@example.org
Answers to Recent Ceiling Fans Questions Posted To This Page
- Question #9509 - Posted: 10/1/2015 4:43:21 PM
Ceiling Fans Question - Emerson Model CF788VNB-72
CF788VNB-72 - http://www.hansenwholesale.com/ceilingfans/emerson/model.asp?ProdNo=CF788VNB-72
QUESTION: I am looking at the Emerson Carrera Grande Eco 72 (DC Motor) Ceiling Fan Model CF788VNB, however regarding fan blades for an outdoor-damp location, would these blades tend to warp over a few years in a humid environment? I have had many outdoor fans, and they almost all end up with warped blades over time. Do you offer blades that would be less prone to warping, or are these already "resistant"?
ANSWER: When you click on the orange button for blades, look for blades that say "(Outdoor Damp)". Emerson specially makes the damp rated blades from solid hardwood (instead of cheap plywood) that is treated to resist cracking and warping from being outside. They will hold up much better than what you have experienced and are in fact rated for use in outdoor damp locations by the manufacturer.
- Question #9508 - Posted: 10/1/2015 4:37:34 PM
Ceiling Fans Question
QUESTION: I just bought a house with a Halsey ceiling fan and I want to add a light to it. The universal light kit only works sometimes! Where can I find Halsey light kits to fit models HC-HP and HG models?
ANSWER: I am sorry to report that Halsey went out of business several years ago, so finding parts for them is difficult. It is not a brand that we ever sold, so we would not have any fixtures on hand that were made by them. If you email me some pictures of your fan, I may be able to determine what types of universal fixtures will fit...if any. Email pictures to: email@example.com
- Question #9507 - Posted: 10/1/2015 4:33:29 PM
Ceiling Fans Question - Emerson Model EM-CF766VS
EM-CF766VS - http://www.hansenwholesale.com/ceilingfans/emerson/model.asp?ProdNo=EM-CF766VS
QUESTION: The location I am considering was wired only for a light and no fan (1 wire pair). How do I tell which lights are compatible and which are not?
ANSWER: Almost all of our ceiling fans with lights do not require a second hot wire, so they will work with a 1 wire pair...there are very few exceptions. If you give us a call, we will be happy to help you choose the best fan for your needs and make sure you can install it.
- Question #9504 - Posted: 11/22/2014 1:30:40 PM
Ceiling Fans Question - Savoy House Model SV-14-325-FD-SN
SV-14-325-FD-SN - http://www.hansenwholesale.com/ceilingfans/savoyhouse/model.asp?ProdNo=SV-14-325-FD-SN
QUESTION: How far down from the ceiling does the Seaside fan hang when installed with the flushmount option?
ANSWER: Thanks for your question: The Seaside fan from Savoy House comes with an 8" downrod as well as a flush mount adapter. The bottom of the fan cage hangs 16.3" from the ceiling when installed with the 8" downrod. Although the manufacturer does not specify the hanging distance with the flush mount option, after reviewing the installation instructions I have estimated that the flush mount option will reduce the distance by at least 6" to be safe...if not a bit more. That would put the bottom of the fan at about 10" from the ceiling.
- Question #9503 - Posted: 7/6/2014 9:23:16 AM
Ceiling Fans Question - Minka Aire Model F820-CT
F820-CT - http://www.hansenwholesale.com/ceilingfans/minkaaire/model.asp?ProdNo=F820-CT
QUESTION: I want to purchase the 36" Down rod DR536-CT (Cattera Bronze finish) $25.13 for the Santa Lucia Ceiling Fan I recently purchased from you. However, when I try to select it the website automatically adds the fan too. Please help
Sorry you are having trouble ordering a downrod. Here is what you can do: Simply delete the fan from your shopping cart to order just the downrod or use this link to add the downrod to your cart by itself:
Minka Aire DR536-CT Downrod
- Question #9502 - Posted: 7/6/2014 9:17:41 AM
Ceiling Fans Question
QUESTION: Do you happen to carry Hunter fan light fixtures that have a triangle base. These are not held in by screws but by a clip system.
ANSWER: I am sorry to report that we do not have any of the Hunter light fixtures you are looking for. Hunter only made the triangular fixtures for a short period of time and they discontinued them several years ago (too many problems). It is unlikely that you will be able to locate one anywhere. If you can email me some pictures of your fan along with the model number (located on a label on top of the fan housing), I may be able to come up with an alternative that will fit. Email your pictures to: firstname.lastname@example.org
- Question #9500 - Posted: 7/3/2014 1:55:05 AM
Ceiling Fans Question - Modern Fan Model VEL-HUG-BN-50-NK-NL-NC
VEL-HUG-BN-50-NK-NL-NC - http://www.hansenwholesale.com/ceilingfans/modernfan/model.asp?ProdNo=VEL-HUG-BN-50-NK-NL-NC
First off, I love all the consumer information Hansen Wholesale provides.
I'd love a clarification on something. You say that hugger fans don't work as well as regular ceiling fans. This makes total sense. However, why would the Modern Fan Velo Hugger be rated at the same 6650 CFM and 5.54 MPH wind speed as the regular Velo?
(Is it because the blades are installed as low as possible on the hugger fan, thus negating the height benefits?)
ANSWER: You are exactly correct. When installed with a standard downrod, the regular Velo hangs down the same distance as the Velo Hugger, so the airflow is the same.
- Question #9499 - Posted: 7/2/2014 11:30:33 PM
Ceiling Fans Question Model SV-58-819-5WA-37
Per the information on the site, the new DC motors, the Emerson K55XL, and other "induction" type motors are considered best quality. If that's the case, how do fans with smallish non-special motors (Say, Savoy House Indira, with 153 x 22mm motor) earn a 5 rating?
There are exceptions. A 5 rating is not just based on the motor inside the fan, but the overall consideration of the quality of the components and performance. Most 153mm motors are only 12mm to 15mm tall and tend to be overworked. The motor used in the Indra is 22mm tall, which is very unusual. This is a special motor that Savoy House had designed for this fan and the performance and quality of the motor are excellent. The 3-blade Indra produces a whopping 8517 CFM and runs very smooth and quiet. The entire fan was designed to produce maximum airflow while reducing noise. The blades have a very special aerodynamic design and the fan runs perfectly quiet. When I saw this fan introduced at the lighting show in Dallas, I was very impressed. Overall, one of the best fans I have rated in years. A DC motor would have been nice...but was not necessary to earn a 5 in my book.
Here is a link to the Savoy House Indra
- Question #9496 - Posted: 6/19/2014 10:09:09 AM
Ceiling Fans Question - Minka Aire Model F513-WH
F513-WH - http://www.hansenwholesale.com/ceilingfans/minkaaire/model.asp?ProdNo=F513-WH
QUESTION: Hi, I have 4 rooms I'm thinking of installing fans. One is 10x14, 2 are 13x14, and a fourth is 23x15. For the first 3 I was considering Minka Aire F513. For the largest room I was thinking about Minka Aire MF-689. Will these be adequate?
Thanks, Tom Kelley
The Minka Aire F513 New Era fans will be great for the 3 smaller rooms. For the larger room, a single ceiling fan will not be adequate...you should install 2 fans. If you install 2 fans, then the F689 Kola-XL 60" fans would be a great choice. If you can only install a single fan, then I would recommend an even larger fan (up to 84") such as the Fanimation Odyn. Here are links to those resources: Large Ceiling Fans
or The Fanimation Odyn
. Please call us at: 1-800-201-1193 and we will be happy to discuss all of your options and help you make an educated decision.