Ceiling Fans: Summertime Savior or Super-Spreader?

Posted by Stuart Heisey on Friday, May 21, 2021

Ceiling Fan Image

With the warm temperatures arriving in the northeast, you may be thinking about turning on those ceiling or box fans, to bring some much-needed relief. But does that additional air movement and associated cooling comfort increase the risk of COVID-19 transmission?

You’re going to love my answer… It depends.

Cutting to the chase:

Based on the discussion below and the analysis Entech has done for many spaces and occupancy scenarios, it is my opinion that increased air movement within spaces will generally decrease the risk of infection, with ceiling fans (either updraft or downdraft) being among the best ways to create that air movement. (To be clear: Air movement alone is not adequate! You must also have fresh air. And perhaps additional strategies to capture, kill, inactivate, or remove the virus, depending on your scenario.)

Since there are many different occupancy scenarios for each building (and even for each space), no one should claim that additional air movement will always result in fewer cases of transmission for COVID-19 or other airborne infectious diseases.

High air movement means that areas of higher concentration of contaminants (dust, odor, droplets, virus, aftershave, etc.) will be spread more evenly throughout the space, increasing the chance of everyone contacting the contaminant, but at a lower concentration.

So if air movement mixes the contaminant throughout the entire room, exposing it to more occupants, why would more airflow (air mixing) reduce risk?

Low or no air movement means that occupants closer to the source will receive the contaminant in higher concentrations. (Example: the closer you are to someone, the more you smell their … aftershave.)

For COVID-19, the data suggests a minimum “viral load” is necessary to cause symptomatic infection. So, if you say “Howdy” to a small viral load you’re not likely to get infected. The larger the viral load, the more likely you become symptomatic. So, when it comes to reducing risk for each occupant, reducing their contact with a high concentration of virus in the air is usually more important (and more practical) than trying to completely eliminate any contact with the virus.

CDC Fan Graphic

The Center for Disease Control (CDC) recommends using ceiling fans to improve air flow (air mixing really), and also recommends not aiming point source fans directly at anyone (which makes people immediately down-wind at higher risk). Both are good tips.

Similar to the CDC, The World Health Organization (WHO) recommends ceiling fans run, but only when some amount of fresh air can also be introduced.

Putting it simply

In most occupancy scenarios, the amount of viral contamination generated by the infected person(s), if evenly spread throughout the room, will not be high enough to cause symptomatic infection for anyone in the room, even though everyone is exposed to some virus. On the other hand, very low airflow and poor air mixing makes it more likely that a few adjacent occupants will be exposed to a high enough viral load to become symptomatically infected.

So, there is some risk in both high air flow and low air flow scenarios. And while there are no guarantees, scenario modeling indicates that more air movement (when combined with some fresh air) generally decreases the risk of infection for individuals. But you should also make your decision based on other data, such as your HVAC system capabilities or an Indoor Air Quality Analysis.

So, the rule of thumb would be to err on the side of more air movement - run your ceiling fans. Oh and plus, they will help keep you and your occupants cooler, especially if there is no AC. Stay cool my friends!

Stuart Heisey, PE Photo

Stuart Heisey, PE


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Categories: Buildings & Campus

Tagged: Mechanical  |  Health & Safety  |  COVID-19

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