Where and how to best place a fan in a room to ensure the best air flow? (video, ~7 minutes)
In this video, Matthias random stuff conducts an experiment focused on airflow and the operation of fans. He begins by using an anemometer to measure the airflow in various locations around his house. Initially, he turns the fan to full power, trying to blow air into the house; however, the readings are unsatisfactory as the fan fails to generate adequate airflow. He then reverses the fan's direction, blowing air out the window, and notices that the anemometer begins to provide more stable readings, although these still fluctuate due to external wind conditions. By connecting the anemometer's sensor to a Raspberry Pi, he can achieve better low-speed readings and monitor data from a distance.
As Matthias continues to roll through his experiments, he realizes that the optimal placement for airflow occurs when the fan is positioned further away from the window, surprising him. After numerous trials, he concludes that a distance of about 1.5 meters yields optimal airflow results. He decides to conduct tests the next morning when the weather is more calm and can observe more reliable outcomes. Matthias emphasizes the joy of collecting clean data and how systematic testing yields clear differences in wind speed based on the distance of the fan from the window.
Furthermore, he tests with another type of fan, and once again, he is surprised to see the variations in air speed performance. Each test reinforces the idea that having the fan closer to the window results in decreased airflow speed. This phenomenon becomes clearer, as the two fans operate based on contrasting mechanics—while one is expelling air, the other pulls air from multiple angles, rendering it ineffective when placed too close to the screen.
Concluding the experiment, Matthias shares his findings. He emphasizes that it’s generally better to blow air out of the window rather than trying to suck it in, advocating for keeping the fan positioned at least half a meter away from the window. He also notes that if there is a gentle breeze outside, it's far more effective to open all windows, significantly enhancing air circulation indoors. Interestingly, he found that a desk fan situated three feet from the window could move as much air as a larger box fan directly positioned at the window, highlighting that even smaller fans can be beneficial if used strategically.
As of the writing of this article, the video has garnered 8,853,884 views and 236,316 likes, showcasing substantial audience interest and the practical value of his air circulation experiment for viewers seeking effective methods to enhance airflow in their homes.
Toggle timeline summary
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Introduction of a visible step function in airflow measurements.
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Discussing the best placement for a fan to circulate air effectively.
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First test of blowing air into the house with an anemometer.
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Switching the fan to blow air out the window; noting slow fan speed.
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Improved readings using a Raspberry Pi for better airflow measurements.
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Getting consistent airflow readings at around 0.18 meters per second.
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Averaging airflow readings and noting external wind affecting results.
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Testing fan effectiveness at different distances from the window.
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Re-testing airflow under calmer weather conditions.
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Identifying optimal airflow at 1.5 meters away from the window.
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Testing a box fan against the window; noting airflow differences.
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Discussing counterintuitive results regarding fan placement.
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Conclusion about the effectiveness of blowing air out vs. pulling it in.
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Highlighting the advantage of opening windows over using a fan in light breezes.
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Surprising comparison between box fan and desk fan air movement capabilities.
Transcription
There's a very visible step function. And, again, a clear step in wind speed when I move the fan. Now, at one and a half meters, I'm actually getting the best readings yet. I want to measure where's the best place to put one of these fans to circulate air through the house. And, I'll close the doors to the rest of the basement. I've got another window facing the same way. And, I'm gonna use an anemometer to measure how much airflow I'm actually getting through the house with that. First test is blowing air into the house. Full power. I was trying to pull air through that window. And, let's see how the anemometer is doing. Nothing. Let's flip that fan around and try blowing air out the window. And, this thing is spinning very, very slowly. And, the problem is this thing is very deficient at displaying very low speeds. So, I wired the sensor in this thing to a Raspberry Pi and that can actually give me much better readings than this device itself at low speeds. And, it grabs it on the screen too. So, now I have this in the same room as the fan with a long wire going over to my anemometer so I don't even have to come in here to check it. Let's turn the fan on blowing air out the window. And, we're starting to get more consistent readings here. We're getting about .18 Come on. Somewhere around .2, .4 meters per second. I think I need to average this over a longer period of time. Unfortunately, I'm seeing a bit of wind outside and that's making my numbers kind of move all over the place. OK, averaging over about a minute I get a quarter meter per second. Now, let's see what happens if I move the fan a little bit further away from the window. And, a little bit of windiness outside is causing some variations but I think it's averaging quite a bit higher. So, I just tried it for a while without the fan running and just a breeze caused some wind. Now, I got it turned back on at 1.2 meters away from the window and it's clearly having an effect. It's just getting gustier outside, messing up all my readings. I ended up taking lots of readings and I graphed those and nothing's really clear other than with the fan further away I get more air flow. It's the next morning and the weather is calm so let's try again. I got my fan right up against the screen and the anemometer is turning slowly but consistently and I do have a little bit of bumpiness but nowhere near what I had yesterday. And, for moving it back, there's a very visible step function for the wind speed. And, again, a clear step on wind speed when I move the fan. I love getting clean data. Very satisfying seeing this thing go round and round smoothly even though I don't actually have to look at it. With the fan this far from the window, I do have to be careful about getting the aim just right. Now, at 1.5 meters or 5 feet from the window, I'm actually getting the best readings yet. Just a little bit higher than before. I end up going back and forth in terms of distance just so I wouldn't be biased by time and then graphing it as a function of distance. The air speed increased as I got further away up until a bit past 50 centimeters or about 2 feet. Beyond that, it stayed pretty much the same even when I went as far as 2.1 meters or 7 feet. The speed didn't drop very much. So, at least for this window and this fan, optimal placement is probably about 2 feet. There's no need to go any further than that. And, now testing with a box fan that is straight up against the window screen. And, the wind speed doesn't appear to be that much higher than it was with a fan. And, I tested again with it further away from the window and further and then closer again. Just moving that fan closer to the screen again, you can really see a step down in wind speed. This is all somewhat counter-intuitive but the reason is the fan is throwing air out the middle of it but towards the edges it's actually sucking in air from the front. So, if that fan is straight up against the screen, it's sucking in outside air. And, graphing the box fan here is right against the window and this is 20 and 30 centimeters away from it. So, more air speed and then this would be 90 centimeters, about 3 feet. So, clearly up against the window is less good than further away. I really meant to get more readings but then this happened. This experiment is done way out of balance now but is one of these oscillating fans really completely ineffective at pulling air through the window? Let's put it right in, right up against the screen. And, that doesn't make enough wind to even move the anemometer. And, that seems counter-intuitive but if you stand behind the fan like that, you really don't feel any wind just in front of it. And, the fan is just pulling in air from all sides. So, why should it pull the air particularly from behind? Which is why a fan like that is particularly ineffective at pulling air in from a window. And, my take away from all this is it's always better to blow air out the window than trying to suck it in. And, move that fan away from the window at least half a meter or two feet. But, if there's even a light breeze outside, you're much better off just opening all the windows because that will completely swamp out what your fan can do. And, the surprise conclusion from all this is that this desk fan, about three feet from the window, will move as much air as this box fan in the window even though the box fan is much larger. Of course, the box fan would do better if it's away from the window too.