Ceiling fans are curious appliances. For some reason, when humans see them, common sense fades and we wonder what manner of fun could be had with the rotating blades. I was listening to a podcast the other day and the presenter, who is an actual and well-known doctor of genetics, was explaining how his family plays a game in which you toss your underwear onto the blades and see how far they fly.
So, when people ask how much weight a ceiling fan can hold, nine times out of ten, it’s because they have some antics up their sleeve. Perhaps I am misjudging you. Maybe you are just wondering if you can use the ceiling fan to secure some bunting or streamers for a party. Whatever your motivation, though, the facts are the facts, and the facts are presented below.
Ceiling fans are not designed to support any weight other than their own. The supporting system (downrod, mounting bracket, junction box, and joist) is designed to hold the weight of the fan. An additional few pounds may be safely added but it depends on far too many variables to be recommendable.
How Is a Ceiling Fan Supported?
There are, of course, variations to this basic model. For example, flush-mount or hugger fan models eliminate the downrod, and a ceiling fan installed between two joists is connected to both via a brace, which comes between the bracket and the joist.
We will just look at the basic support system for simplicity’s sake.
Downrods and Brackets: Weight-Bearing Capacity
I have been researching ceiling fans for a while now, and in the course of my research, I have never come across a ceiling fan manual or spec sheet that lists the weight-bearing capacity for a downrod or a bracket.
However, as these two parts come with the fan, it is safe to assume that they can support the operational weight of the whole fan.
A ceiling fan typically weighs between 8 and 50 lbs, so you should expect the weight-bearing capacity of its mounting parts to fall within that range. It is a rather broad range, which means that you will have to look at the owner’s manual to see the actual weight of your fan.
Junction Boxes: Weight-Bearing Capacity
Junction boxes do not typically come with the ceiling fan, and they are not specific to fan installation. They are required by code for every electrical project that involves a wiring connection. This means that there are different types available.
For a ceiling fan, the junction box performs the dual function of housing the electric wires and supporting the weight of the fan. As a result, regular junction boxes, which are designed to support things like light fixtures, aren’t always suitable for ceiling fan installation.
Instead, ceiling fans are to be mounted on fan-rated junction boxes. Fan-rated ceiling fan boxes will state the maximum weight or weight range that they can safely support. Many are rated for 50 lbs but you do get some that are rated for up to 75 lbs.
The junction box used for a ceiling fan must always be rated for weights greater than that of the ceiling fan itself and this rule is reflected in the manufacturer recommendations.
For instance, the Minka-Aire F5240WHF (amazon link) weighs 10.36 lbs but the manufacturer recommends that the outlet box should support at least 50 lbs. Another example is the Hunter Dempsy Low Profile Fan (amazon link), which weighs approximately 18 lbs but the recommended junction box weight-bearing capacity is 70 lbs.
The reason for this seemingly excessive support is something called dynamic load, which you will need to understand in order to accurately and safely determine how much weight your ceiling fan can hold. Before we get to this important concept, however, we are first going to look at the final supporting point of the ceiling fan.
Secure Junction Boxes to Joist
In addition to the junction box having to be rated for ceiling fans, they also have to be attached to the ceiling joists. This makes sense because drywall cannot hold the weight of a ceiling fan, so your ceiling boards would collapse.
Your ceiling joist is part of a structure designed to hold the whole house up, so this is certainly not what chemists would call the limiting factor in the case of how much weight a ceiling fan can hold.
What Is the Dynamic Load?
Now we come to dynamic load.
Anything with a static mass (i.e., all matter) will develop a dynamic load when put into motion. This dynamic load will be greater than the static mass because you are increasing the number of forces acting on the object.
A static ceiling fan is being acted on by mass of the fan and gravity. When put into motion, you add the force of velocity. Why is this important for us to know with regards to how much weight a ceiling fan can hold?
Quite simply, it is important because the mass of a fan as indicated by the manufacturer only refers to the static mass.
Rotational dynamic load is also known as centripetal force. It is measured in Newtons and it is represented in the following equation:
Here, Fc is the centripetal force, m is the mass, v is the velocity, and r is the radius.
Mathematically, a fan’s dynamic load is directly proportional to the fan’s mass and velocity, and it is indirectly proportional to the fan’s radius.
If you don’t know what it means for something to be directly proportional, it means that when the static mass and/or velocity of the fan increases, so too will the dynamic load, and if the radius of the fan increases, then the dynamic load decreases.
How Added Weight Influences Rotational Forces
If you never turned the fan on, then the maximum allowable weight you can hang from the ceiling fan is the difference between the weight of the fan and the maximum amount of weight the junction box can hold.
When you do turn the fan on, dynamic load enters the system and complicates things. I hope to un-complicate it for you.
As far as I can tell, the allowable weight of a fan hanging from a junction box is about 20-40% of the weight rating of that box.
So, for a box rated for 50 lbs, this means it can handle a weight of 10-20 lbs. The rest of the weight-bearing capacity of the box is allocated to deal with the centripetal force.
If you took a 42″ fan weighing 16 lbs, then you would have approximately 4 lbs of weight to “play” with.
Before you go attaching your 4 lbs items to the ceiling fan, however, remember that the relationship between dynamic load and mass is not isolated. There are other forces that come into the equation, namely velocity and radius.
Influence of Velocity
Taking our 42″, 16 lbs fan, let’s further assume that there are two speed settings. One setting is 200 RPM and the other is 400 RPM (average low and high speeds for ceiling fans).
On the low speed setting, the fan has a dynamic load of 1,697.6 N.
On the high speed setting, the fan has a dynamic load of 6,784 N. As you can see, this is a massive difference.
Now, add 4 lbs and we get dynamic loads of 2,122 N and 8,480 N on the low and high speeds, respectively.
Assuming that fan manufacturers calculate the centripetal force that a fan can handle based on the weight of the fan and the highest velocity that the fan can achieve, then our hypothetical fan can handle a dynamic load of up to 6,784 N.
If you add 4 lbs and put the fan on the lowest setting, you don’t exceed this but as soon as you switch it to the high speed setting you do, and the fan becomes dangerous.
The Role of Radius
Finally, let’s look at how radius plays a role. If you increase the radius, you decrease the dynamic load of the system.
If you can find a 52″ fan of the same weight (16 lbs), then at a high speed, the dynamic load (the hypothetical maximum allowable dynamic load) is 5,480 N. This is lower than when the fan was 42″.
Adding 4 lbs makes the dynamic load 1,714 N for a low speed setting, and 6,850 N for a high speed setting.
So, the higher speed setting with the increased weight still produces a dynamic load greater than our presumed maximum allowable load. However, the difference is smaller. The difference is 1,696 N in the first scenario and 1,370 N in the second.
To confirm the trend, I performed the calculation for a 72″, 16 lbs ceiling fan and obtained a difference of 989.4 N.
Increasing the size of a fan without increasing its weight will increase the amount of additional weight you can add. The rate at which this happens, however, is too slow to be realistic, particularly considering the fact that you are not likely to find a large enough fan with such a small mass to make the maths work.
Where the Additional Weight is Added
One final consideration is where you are adding the additional weight.
The weight rating of a junction box is the weight rating of the junction box. It’s not the rating for the fan itself. This means that, technically, we have no easy way of establishing how much weight a ceiling fan can hold.
In order for all that we have learned so far to be applicable, we would have to attach the additional weight in the correct location.
Let’s go through a hypothetical scenario to demonstrate this. Let’s say you want to hang from the ceiling fan (please, don’t).
If you were to hold onto the downrod, then your weight is being supported by the whole ceiling fan support system. Grab onto a blade, however, and your weight is exerted on the bracket securing the blade to the body of the fan, and it will bend if not break off entirely.
Don’t Hang Anything From a Ceiling Fan
With careful calculations, you can probably work out how much weight a ceiling fan can hold, and if you attach this additional weight to the fan correctly, you might not face any negative consequences.
However, in my opinion, the only things that should hang from parts of the ceiling fan are other parts of the ceiling fan. What I mean by this is that you can hang the fan body on the bracket and junction box, and you can hang the light fixture and blades on the fan body.
You even need to be careful about replacing or upgrading the ceiling fan blades. If the new ones are heavier that the old ones, it can cause trouble.
Perhaps a bit of mistletoe to spice up your Christmas party, a couple of lightweight ribbons, etc., these are not going to cause an issue. Anything else should be avoided.