> CDC recommends not using a fan at temperatures above 32.2°C
I don't know quite how to put this, but are they idiots? I don't quite mean that, but at the very least there's something weird going on. I double down on this as they double down on their recommendation at the end of the article.
Go to places like India, and see how people use fans, in the humid places like Kolkata and the dry places like Hyderabad. Fans obviously provide great relief at far higher temperatures than their 90°F. The very idea of suggesting not to use fans from such a low temperature is, to me who grew up in Melbourne, Australia and now lives in Hyderabad: ludicrous.
Even when they talk about "people who are less able to cope with heat", it sounds like they may be giving advice very harmful to normal people, for the possible but highly contested safety of a few.
——
When talking about ineffectiveness of fans in high temperature low humidity (which is Hyderabad summer to a tee—it barely gets below CDC's 90°F, and is very dry), the details mentioned make me sceptical of the entire approach of the studies. I know each time I've come to India, it's taken me well over a week to adjust to the temperature. (I still sweat more than most Indians do, but not as much as a day or two after I come.) And hydration is a rather important factor too, likely not accounted for adequately. We're talking definite heat stress circumstances, you can't expect to get accurate results from an unacclimated body.
Yes, I am a layman casting doubt on the work of experts without investigating carefully. I imagine they've been at least somewhat careful about these things, none of these people will be idiots. It's probably not all as bad as the vibes I'm getting. Do treat my scepticism with scepticism of your own.
> The dueling conclusions underscore the tricky balance facing public health agencies, says Kristie Ebi, a heat epidemiologist at the University of Washington. “The messaging needs to be simple,” she says—but not too simple.
It’s the COVID garbage all over again. They think the public are absolute drooling morons who cannot be trusted with any nuance, and they bake this prejudice into their recommendations.
Good lord, we are never going to be able to rebuild trust in our institutions if they haven’t learned any lessons over the last 5 years.
You know, I might be dumb as a stump, but I am pretty sure I can tell if a fan makes me feel cooler on a hot day…and if an expert tells me I am wrong, I’m going to ignore them.
"They" aren't aliens. "They" come from that same public, and are as much drooling morons as the rest of the public (what i frequently remind to the Russians who whine about the Russian government).
>to rebuild trust in our institutions
will see how appointment of Kennedy Jr. as the health services tzar would work here :)
Popular thinking among the Russian opposition is that the way Western societies reacted to Covid demonstrated to Putin the loss by those societies and by their institutions of the ability to act reasonably. And the inept reaction to the war in Ukraine seems to confirm that.
I'm 100% with you. I grew up in a place where winters can be fairly chilly - 0-10℃-ish, but in the summer it can go easily over 40℃.
Fans are an absolute necessity. Classrooms without fans mean kids sleeping in class due to overheating. Being at home without a fan is an absurd notion (unless you have AC, of course).
Go out in a hot day when the air is mostly still, and feel the relief every time the smallest breeze flows by.
Skin has natural heatsinks, especially sweat. Blow air onto them and their efficiency multiplies. We should all know this - we put big fans atop CPU/GPU heatsinks for a reason.
This reminds me of a social studies teacher I had all the way back in like 1993. It was hot in the classroom and students would make paper fans and fan themselves. The teacher told us that the motion actually generates more heat and makes you hotter.
He was right technically of course - 30 students waving something will probably heat up a windowless classroom a degree or two - but it still felt much better to have the air movement.
The room I'm in now does get hot, and a fan pointing inward with one closed window doesn't help me feel more comfortable, but if I open 2 windows and have a fan pointing outward to create a current, it's great. Fans can blow hot air in an enclosed space and be unhelpful.
Before discounting it, I think the article has some very interesting, non-obvious conclusions. Fundamentally that, in humid conditions, fans are more effective at higher temperatures, while in drier conditions, since most of the sweat on you will already have evaporated away, fans in dry environments are only useful up to a lower temp, as after that they act like a convection oven.
The article did mention some studies spritzed participants with water, but didn't seem like they tested it across all possible conditions. Seems like spritzing yourself with water even in a dry environment would make a fan still a benefit at higher temps, given the proposed explanations in the article.
I don't discount it entirely, but as I remarked, I'm sceptical of that entire methodology, because it doesn't sound like they've controlled for acclimation, which experience says has a significant effect, and because the result itself is (perhaps consequently?) surprising.
I think this might be meant for an audience for which the choice is not between fan and no fan, but fan and some other cooling mechanism (an AC). If you can use an AC, definitely prefer that at such temperatures.
If the American population had to face hot and humid climate like that of North India, there will be an uproar and some big central solution pushed very quickly.
I've lived in Hyderabad for more than the first two decades of my life without air conditioning and then moved to the US living in Texas and then the north east.
I 100% agree with your sentiment, fans work even at 110F.
I don’t get it either. I haven’t read the article but it always feels like a fan increases the rate at which my sweat evaporates, making me noticeably cooler. This was in the Middle East where in the shade temperatures easily go above 45C/113F in the summer
>> CDC recommends not using a fan at temperatures above 32.2°C
>I don't know quite how to put this, but are they idiots?
I can't believe they said that. They need to move anywhere in the US Southern region. 32.2C is a cool day reprieve in a Southern summer and fans are a necessity.
>under the hot and dry conditions, however, the fans increased body temperature, the strain on the heart, and thermal discomfort. In other words, the fans worked better at higher heat index temperatures.
>There’s a physiological explanation: When air temperature soars above skin temperature, then the exchange of air between the body and the air switches; rather than dissipating away from the body, heat from the hotter air starts to flow into the body.
Nathan B. Morris, Timothy English, Lily Hospers, et al. The Effects of Electric Fan Use Under Differing Resting Heat Index Conditions: A Clinical Trial. Ann Intern Med.2019;171:675-677. doi:10.7326/M19-0512
Searching the doi on google scholar reveals the stuyd, published in 2019, has 75 citations so far
You linked to the very paper the article is about, which is referenced in the fourth sentence of the article, indicating you didn't spend a single second reading the article before commenting.
This article is IMO quite a stretch based on the actual data.
> New research from two different groups of thermal physiologists favors the higher temperature limits, especially in humid weather. But the groups don’t agree on a single temperature threshold. One study, published on 6 November in The New England Journal of Medicine (NEJM), reports that fans can relieve stress on the heart in elderly people in humid conditions at 38°C. The other, published on 17 October in JAMA, concluded there was little additional benefit from using a fan above 35°C.
The NEJM article is pay-to-read. The JAMA article took older adults, had them sit in a room at 36C, for 8 hours, getting very occasional light exercise and tested three different air movement speeds. The body temperature of the subjects was 38C, independent of fan speed, from which IMO one can conclude approximately nothing other than that the subjects' bodies were warmer than ideal under those conditions.
In my personal experience, the effect of air movement and body movement under conditions like this is dramatic. "Resting" (as the study had the subjects do) in the daytime (as the subjects did) is, for me, not so pleasant. Add a fan, and it's less unpleasant. Riding a bike can be very pleasant as long as there's plenty to drink. But I suspect that my rectal temperature would be more or less independent of any of this.
But public health agencies warn that if it’s too hot, the blowing air can actually make things worse by acting like a convection oven—and they differ on that threshold.
This is a real problem. A lot of people are found dead sitting in their closed apartments in front of a fan, thinking it would cool them off during a heat wave.
Yes, the CDC is trying to give advice that won't kill vulnerable people - if they get it wrong, people die. Imagine that's your job every day. Whether healthy young people are comfortable is very secondary.
One might imagine the solution to that problem is, 'don't use fans', but that would result in people dying from heat illnesses. They need to find a threshold that minimizes those very bad outcomes.
In theory, wet bulb should be used by weather reports on hot days, but for some reason it's not. IIRC it's hard to measure or to universalize - that is, it's hard to produce a consistent, meaningful, clear metric.
Yes. My point is that there isn't a consistent, reliable method to define, measure, and communicate that. And without such a method, authorities like the CDC can't make recommendations that may affect life and health.
I agree. The article mentions all of this... when it gets that hot, especially with US-Midwest humidity levels, you need evaporative cooling with "just a fan". The phase change absorbs energy and can provide relief to higher temps.
All moving air does is increase the rate of the heat transfer from the higher temp substance to the lower temp one. If the air outside is hotter than your body temperature then a fan will be heating you UP not cooling you DOWN.
Without electricity or chemical reactions the only way to stay cool in high heats is to use evaporative effects. Evaporation is endothermic (takes in heat) and actually cools down the thing being evaporated off of. So you can basically soak your shirt and as it evaporates it cools you down. There are things called 'evaporative vests' which can cool you off for hours.
I wouldn't dispute that there's a very narrow band of temperature differential and air flow rates where the speeded up rate of airflow increases evaporation cooling effects enough to compensate for the faster rate of heat delivery from the air itself. The hotter the air tho, the slower you'd want your fan to be, in this narrow range of conditions.
I’d replace top with something like: A fan isn’t directly helpful, unlike an AC it’s not going to cool an empty closed room. However, it can make a wider range of temperatures and humidity levels comfortable through aiding evaporation or bringing in cooler air when possible.
This is why as the article mentions a fan alone can be worse than doing nothing in sufficiently hot and dry air. People only sweat so fast so at some point without supplemental moisture the fan acts like a convection oven simply warming people faster. This can be offset by adding supplemental moisture via a 'evaporative vests' or mister the maximum temperature increases.
This and other reasons mean health organizations are concerned with finding and communicating the maximum temperature fans are still useful.
If you think about it, fan use during super high heats could lead to fatalities, because people using them could possibly be so hot, they're not even able to realize the moving of hot air over them is actually heating them up more. Anyway, like I said the only REAL solution is evaporative effects, if there's no AC to be had.
> So you can basically soak your shirt and as it evaporates it cools you down. There are things called 'evaporative vests' which can cool you off for hours.
Or like, sweat? Which is something people who aren't dehydrated tend to do at or above 95F (35C).
I spend a lot of time riding my bike in the summer here in Massachusetts. Temperatures regularly get up to around 35 °C (95 °F), but fortunately the humidity isn't usually too bad. These rides are usually at least two hours long, and sometimes up to six. I'm always surprised at how tolerable those temperatures are when air is moving by you at a decent speed. It definitely requires a lot of water and mineral replacement to sustain. Aside from having to make more stops to refill and pay closer attention to hydration, I surprisingly find it more pleasant than riding at 30 °C (86 °F).
Weird! I replied to that comment because I didn’t think they mentioned humidity, though I see they did. I appear to have just completely overlooked it. Sorry about that!
While this is an exaggeration, it really is very very bad. I have stayed for short amount in very hot and humid areas where sadly electricity was rare and yes you just want to get out of there as soon as you can.
It makes a huge difference if you get introduced to high temperatures and humidities over a period of weeks or months rather than all of a sudden. People live in hot climates year round without feeling miserable all the time. Most bodies are able to do a surprisingly good job of adapting to high temperatures if the transition is done very gradually.
Living in hot and humid climate is miserable even for people living there all the time. Yes humans persist and carry on but it doesn't make it less miserable, and any lucky person who was able to escape will never ever want to go back to that lifestyle.
I wouldn't want to live in an environment that's basically too hot for human life to thrive. There are people all over the world right now living in areas that are genuinely deadly if the AC goes out. People say "Oh, we do just fine in Death Valley, etc" (the American West in general) and that's just a person who is alive only because of AC. lol.
> but out of curiosity how much of your time do you spend in air conditioned environments?
Over 30y, I can give all possible answers to that question. I was 15y in scouting leadership. During June-Aug, I would be outdoors for weeks at a time. What I got used to was feeling sick every day.
That said, early heat stroke symptoms get old after a decade or three. Now I go outside after sunset.
I've never even thought about whether evaporative cooling CAN happen in like 100% humidity? Whether from sweat or from wet clothing. It seems like if there's so much air moisture evaporation can't happen, and the additional kinetic energy of hot water molecules just seems like energy that simply cannot be gotten rid of. Maybe one of my personal troll followers can look this up on ChatGPT and tell me I'm wrong? :)
The article mentions but doesn’t do a good enough job explaining at high temperatures and low humidity a fan can remove sweat faster than your body can supply it. Making excessive fan speeds counter productive and actually increasing body temperatures, ie there’s humidity + temperatures where low works better than high and edge cases where even low is counterproductive.
This flips with supplemental water which once again makes faster fan speeds useful up to significantly higher temperatures. Obviously there’s another limit as a mister alone can’t lower a rocket engine exhaust to be comfortable.
Net result a lot of seemingly contradictory recommendations shown in the article.
Yeah as a BSME I'm well aware of what sweat does. That's your body's way of doing evaporation cooling. But if you want serious cooling effects then wet clothing can basically make the difference between life and death in extreme conditions. It's a valuable skill to know. Saying "Just sweat" is not a skill to know.
"... results in dry conditions starkly illustrated the dangers of misusing fans. The scientists stopped the experiments after testing just 14 people because their cardiac stress went through the roof as the fan blew hot air on them. Nearly half the participants couldn’t stay in the test room for 3 hours. The reason for that dramatic response: The air was so dry that any sweat quickly evaporated, resulting in little additional cooling as the fan bathed participants in extremely hot air, Jay says."
Why would faster evaporation result in less cooling? I could make some guesses but I wonder what the reality is.
Possibly, they mean that the evaporation was exhausted quickly and after that, it was just a convection oven.
evaporation done with hot wind has two effects working in opposite directions. The evaporation is a cooling effect, but the hot wind is a heating effect. So if the hot wind is moving too fast or is too hot, it's effects will be larger than the effects of any evaporation, resulting in heating rather than cooling, due to increased airflow, or too high a temp.
I wasn't correcting or disagreeing, just providing more info that there's two effects going on. Hot airflow always adds heat, and evaporation always reduces heat, so you only get cooling if the evap energy loss exceeds the heat transfer rate.
Its because of thermodynamics. When you use fans in an area that doesn't have other external circulation, you introduce more energy into the system. This will increase increase temperature. From personal experience for a closed room, fans don't help if temperature even reaches 27degC. If the temperature outside exceeds 35 degC or basically any comfortable temperature, the result will depend on humidity levels. If you are sweating, it will help because of evaporation - some energy is absorbed for the phase change. If its really dry, a fan will only make it worse.
> When you use fans in an area that doesn't have other external circulation, you introduce more energy into the system. This will increase increase temperature. From personal experience for a closed room, fans don't help if temperature even reaches 27degC.
Why wouldn't blowing 27C air over your 37C body cool you off? The fan isn't adding 10C to the room temperature (or you need a new fan).
- The HN title is misleading. The real title is "When is it too hot to use a fan?"
- The article explains: "The key point: Above 35°C, humidity matters a lot. In very dry conditions, a fan could be counterproductive, whereas in very humid ones it could continue to help at much higher temperatures." They quote two controlled studies that show the same results so there's no reason to debate this.
It's just a bad title. There's nothing controversial here.
I don't know quite how to put this, but are they idiots? I don't quite mean that, but at the very least there's something weird going on. I double down on this as they double down on their recommendation at the end of the article.
Go to places like India, and see how people use fans, in the humid places like Kolkata and the dry places like Hyderabad. Fans obviously provide great relief at far higher temperatures than their 90°F. The very idea of suggesting not to use fans from such a low temperature is, to me who grew up in Melbourne, Australia and now lives in Hyderabad: ludicrous.
Even when they talk about "people who are less able to cope with heat", it sounds like they may be giving advice very harmful to normal people, for the possible but highly contested safety of a few.
——
When talking about ineffectiveness of fans in high temperature low humidity (which is Hyderabad summer to a tee—it barely gets below CDC's 90°F, and is very dry), the details mentioned make me sceptical of the entire approach of the studies. I know each time I've come to India, it's taken me well over a week to adjust to the temperature. (I still sweat more than most Indians do, but not as much as a day or two after I come.) And hydration is a rather important factor too, likely not accounted for adequately. We're talking definite heat stress circumstances, you can't expect to get accurate results from an unacclimated body.
Yes, I am a layman casting doubt on the work of experts without investigating carefully. I imagine they've been at least somewhat careful about these things, none of these people will be idiots. It's probably not all as bad as the vibes I'm getting. Do treat my scepticism with scepticism of your own.