When the outside temperature is sweltering, it can be tempting to leave the ceiling fan in a room running so that the room is cool and inviting when you step back inside. Our brains naturally associate the action of a fan with cooling, so it seems to make sense to leave the fan running to cool a room, even if it is empty.
We all know someone who runs the ceiling fan 24/7, no matter the time of year. Let’s examine whether leaving your ceiling fan running in an empty room is ever a good idea or if it should be switched off each time you vacate a room.
A ceiling fan does not affect the actual overall temperature of a room. Leaving the fan on in an empty room is a waste of electricity if cooling is the aim. If the aim is keeping flies away from food or aiding whole-house or local ventilation, then running the fan in an empty room can be useful.
Ceiling Fans Cool People, Not Rooms
A ceiling fan’s effectiveness is limited to the area where the air movement can be felt. Unlike an air conditioner that actively cools the air, a fan is simply twirling the air around and creating a breeze-like effect (when set in summer mode).
That is not to say that a ceiling fan won’t make you feel cooler on a hot day. It’s just that the mechanism differs from that of an AC or similar appliance.
Cooling Mechanism of Ceiling Fans
The rotating fan blades create a cooling effect by actively moving air over your skin. This constant movement of new air makes it feel cooler due to convection and evaporation. Here’s how it works:
Our bodies are designed to keep our organs warm, but not too hot. A thin boundary layer of air, close to our skin and heated by our own body heat, helps us stay warm.
Running a ceiling fan when it is hot causes a wind chill effect. This is when the air moving over our skin essentially steals the heat from the boundary layer of air and carries it away. More body heat is released to replace that which was lost and a cooling cycle begins.
In addition, the moving air causes any sweat on your skin to evaporate faster. The more evaporation takes place, the cooler you will feel.
While the rotating fan will not make any difference to the temperature of the furniture or inanimate objects inside a room, it certainly can provide relief to those who are close enough to feel the air movement generated.
An excellent way to think about how a ceiling fan works is to imagine ladies’ hand fans in times gone by. The user was able to cool her face by agitating the air around her face manually to provide relief. The fanning action did not benefit anyone in the room beside the person holding the fan.
So, based on the cooling mechanism of a ceiling fan, we can conclude that running it in an empty room serves no cooling purpose.
Cooling Is Instantaneous
Unlike ACs, switching on a ceiling fan when you enter the room creates an immediate and direct cooling effect. So, there is no need to leave it on while you are not in the room if your goal is to feel cool when in the room.
Continuous Running of Fans May Heat Rooms
There is even the suggestion that leaving a fan running in an empty room is more likely to warm the room slowly than have any noticeable cooling effect.
Some of the power used to run the fan mechanism turns to heat, so keeping a ceiling fan running in a room without occupants would be ineffective in creating a pre-cooled environment.
Running Fan in Empty Room Wastes Electricity
Most of us are very aware of our electricity bills and carbon footprint and like to find ways to live comfortably while being as budget-conscious and green as possible.
Although a ceiling fan uses a lot less electricity than most heating or cooling systems, on its own, it cannot exert any change on the ambient temperature in a room.
When the weather is extremely hot, you can often justify extra electricity usage from running the AC to keep a room cool even when you are not in the room (like cooling a bedroom before going to bed).
The same is not true for ceiling fans despite the fact that they are more affordable to run for long lengths of time. The electricity usage of leaving a fan on in an empty room will be low, but all that electricity will be wasted.
While it is not an actual air circulator, a fan does circulate air in the room (if this confused you as much as it used to confuse me, check out Difference Between Air Circulator and Fan).
This means that leaving a fan running in an empty room may serve other, non-cooling purposes of which you can take advantage.
Using the Fan to Keep Flies off Food
Having a ceiling fan situated over a counter, kitchen table, dining area, or even an outdoor covered porch is an effective method of keeping pesky flies from landing on food. If you have ever tried to swat a fly, you know they can be ultra maneuverable but they don’t cope well in windy conditions.
A ceiling fan can be an efficient and natural method to keep flies off food even when the room is empty, which is one of the reasons installing a ceiling fan in the kitchen can be a good idea. The air current created by a powerfully moving ceiling fan is a major deterrent for these pesky bugs.
Fan Helps Provide Whole-House Circulation
A ceiling fan is an excellent, cost-effective way to get air in a room moving. Although it is not usually beneficial to run a ceiling fan in an empty room, in some circumstances, it can help provide greater air circulation throughout the entire house.
The whole-house effect will depend mainly on a few key considerations. Let’s look at ways a ceiling fan may be helpful to get air moving through more than just the room where it is located.
The Size and Speed of the Fan Matter
An average ceiling fan spins at around 350 RPM, which is not powerful enough to create a current in other areas besides the immediate room in which it is located. However, there are plenty of variables, and depending on the length of the blades, the setting, or the motor’s power, it might be possible for a ceiling fan air to move air through a room and its effects to be felt in nearby areas.
Open Plan Settings
The presence of doors and walls naturally limits the air current created by a ceiling fan. Fully opening doors in the room that contains the ceiling fan will facilitate air movement from the fan to a larger area.
The more open-plan an area is, the fewer air-circulation boundaries and the more likely the effects of a ceiling fan may be felt in a broader area of the home.
Use Ceiling Fan in Conjunction With Other Devices
As already mentioned, ceiling fans typically only serve the area immediately around them. However, a ceiling fan can effectively team up with other devices like pedestal fans, air conditioners, or even simply opening the windows to move air around and aid in whole-house circulation.
The Position of the Ceiling Fan
A ceiling fan can help in whole-house air circulation if it is strategically positioned.
For example, while it is impossible for a ceiling fan to cool the temperature of the air on its own, a powerful fan located in an entrance area of the house could create a draft of cool air from an open doorway, especially if there is a window or other opening elsewhere to provide a cross draft.
If a ceiling fan is positioned strategically in an area where it can distribute air currents to other areas, there may be some value in keeping it running even when the room is empty.
Moving Cool or Humid Air
Although a ceiling fan cannot cool air itself, it can be harnessed as a tool to move cooler air from colder areas and displace the air in warmer rooms. Some rooms naturally stay cooler than others, for example, a basement or windowless pantry.
Using a ceiling fan in conjunction with other mobile devices like a cleverly placed pedestal fan could be useful to move cool air into warmer areas. A ceiling fan may also be helpful in distributing humidity in the same way, only with the goal of spreading out the moisture in the air as opposed to the cold air.
Local Ventilation Is Required
Leaving the ceiling fan running in an empty room with an open window is an effective way to add a bit of fresh air when necessary. While there is no ventilation exchange of air that a fan can do on its own, opening a door or window while leaving the fan on will facilitate the exchange of old air with new.
This can be especially valuable in areas like a nursery where there are messy diaper changes or over craft areas where gas-emitting substances like glue or paints are used. By the time you return to the room, the ceiling fan will have had time to waft the smelly air out and pull some of the clean air inside.
Keep a ceiling fan running in freshly painted rooms to keep the air moving. This will not only diffuse fumes, but the paint will also dry faster.
What About Running the Fan in Winter?
A ceiling fan cannot change the temperature of a room, even if it is set in winter mode. However, it can be an effective tool to move air heated by another source around the room and distribute it more evenly.
Setting a fan on winter mode changes the direction and action of the blades. Instead of creating a downward breeze directly below the fan that causes a wind chill effect on the occupants, switching the fan blade direction pulls the air in a space up towards the unit.
Warm air naturally rises and collects around the ceiling, which is not terribly useful for anyone trying to stay warm at floor level. So, when using a heating appliance like a space heater or radiator, running a ceiling fan in winter mode can help distribute the heat more evenly throughout the room.
Running a fan in an empty room with a heater ensures that the room will be at an even temperature throughout when you step back inside. There is no point in running a ceiling fan in winter mode without any external heating devices since the fan itself cannot generate any significant heat.