Experiments and anemometer measurements to figure out where to best place a fan to optimally air out the house to cool it down at night. More physics experiments: woodgears.ca/physics
I have cooled my entire house in the summer like this for years. Pick a window on the upper floor, or at the farthest point from your bedroom. Open all of the windows in the house. Wait until the temperature outside drops below the interior temperature and then turn on that fan and blow the air out of the house through a single window. This will take in cool air from the outside. Then in the morning as the temperatures rise, close all of the windows again. You will be amazed at how much cooling effect you will have without resorting to air conditioning.
I have relied on this technique all summer long for several years now. Northwest United States here, so the weather often gets up to 95° but cools off at night. By managing the windows and fans as you described, we don't even need air conditioning. (Bought one anyway, just in case of wildfire smoke.) It's especially effective in a tall building, like a two- or three- story house. Once the windows are closed and the air gets still, warm air floats up to the top while the lowest floor is much cooler.
@@dardanpaloka4413 Usually around 40-60% here in the Pacific NorthWest (which is weird, considering our reputation for eternal rain.) That's a critical factor I meant to volunteer in my post. In a humid climate, you just need something with a condenser. Acclimation, shade and humidity matter more to me than the thermometer reading.
I bet, like me, you also hate recipes online that have 24 paragraphs about how they came to discover the recipe and their life story before they get to the recipe.
I am an Italian firefighter, this is the same principle we use to evacuate the fumes from the houses during a fire, the "cone" of air must cover most of the window opening
@@matthiasrandomstuff2221 could you repeat your experiment with some simple ducting? Just foam board or something cheap and easy to throw together? I find ducting to be far more important than individual fan characteristics or performance.
@@matthiasrandomstuff2221 could you repeat your experiment with some simple ducting? Just foam board or something cheap and easy to throw together? I find ducting to be far more important than individual fan characteristics or performance.
My father, an civil engineer, was doing this experiments back in the 60's at our house. It was a big house. Finally he sealed/placed the fan in a stair way window and kept the inside doors in a closed circuit, porch to kitchen, to living room, hall way and ending in master bedroom. We never had to run the AC until June then only in the afternoons. (Atlanta GA area).
@@eggbenedict-gt7mw First of all he said his dad was a civil engineer, not that it was required, but that distinction probably went over your head. You're so desperate for attention you replied a comment without data, and said you did better, despite it being impossible to prove that.
My granny also lived near Atlanta. She always put a box fan in the front door. In the daytime, she would have it blowing outward to push hot air out. In the evening, she would turn it around to pull cool air in. She never had an air conditioner and it was always relatively nice inside her house except on the hottest days of summer. It helped that she had two massive oak trees shading her house.
This actually makes sense to me, In Firefighter training here in Germany we get told to put up a fan at a distance where the cone of wind coming of the fan covers all of the Door / window. (We use large fans to air out homes full of smoke)
I'm guessing the initial air flow drags additional air surrounding it,producing a larger flow at a distance, (I can't remember the name of the effect.. It's not venturi, but one of those. anyway, if the fan is at the edge of window, only the air straight through the fan is evacuated, while the air dragged along is outside air. If the fan is further away, it drags a larger amount of inside air and pushes it outside.
@@maximeteppe7627 It is "The Venturi effect" and he made video about it 9 years before he made this video... ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Na9ORhYjvJU.htmlsi=kdDp1AZNLgxYqog4
Right! Most RU-vidrs have the 3 min intro music, 5 min explaining what they are going to show in the video, NordVPN segment, then 10 min later they finally get to what the description says 🤦♂️
@@barrioscorona215 I don't think it is right to expect the creatoers to not earning money through ads for their sometimes extremely high quality content, costs and effort they put in to their videos. With your favorite TV shows you also don't complain about intros. It is just part of the whole thing.
@@Deinecraft You are right about the ads but for sure some RU-vidrs have this over the top intro and that can be annoying. I like how this guy's immediately gets to the point. I don't mind the ads but what does bother me is over the top into with the music, then the sponsor and before you know it you're like 6min into the video. Like put the sponsor in the middle or something. Idk but I agree with you.
Racheal: "Do we really have to keep this fan in the middle of the room?" Matthias: "IT'S OPTIMAL! And it's NOT in the middle of the room. It's precisely 52.068cm from the window!"
As a physicist who worked in an office with no air conditioning, this was one of the experiments I had to undertake. Very often I would get to the office at 06.00 or 06.30 and the temperature in the office would be about 28°C. Outside air temperature was about 20°C at this time. Subjectively it was very noticeabble that blowing air out of one window enabled the other window to suck in cool air from outside. --> blow out is best, imagine the ventilator generates a "cone" of moving air which causes other air to also be moved. Aim for the largest vigorous moving part of the cone to be at the window. The next factor was whether closing the windows when the outside air temperature exceeded the inside temperature or whether to leave them open in the hope that there might be a breeze occasionally. --> This was conclusive - keeping hot air from outside out (typically 35°C in the mid afternoon) and the cool air in was best. The last objective factor was avoiding the sun heating objects (desks etc.) inside the office. For this, outside venetian blinds had to be adjusted so that sun did not shine directly on objects inside the office. This made a small but still appreciable improvement. One subjective factor is to use a ventilator to move the air in the office. Actually this should cause a miniscule temperature increase (the ventilator uses a motor consuming non-negligible amount of electricity converting into work, but SUBJECTIVELY the air moving over slightly moist skin feels cool. (But it isn't actually cooler, of course). I use these tricks also at home to ensure my house stays cool (we have no A/C) even though outside can be 39°C. Recently I had a 12° cooler house inside compared to outside. Whether in the office or at home I always make sure I can reliably measure the temperature in all required rooms and outside. Perception is subjective, thermometers are objective! All the best, Rob in Switzerland
I am no physicist, but woul'd moving air not increase the evaporation and so cool the evaporation surface/ object (in this case you), so it would not be a subjective feeling, but an actual cooling effect for humid objects?
@@rabenklang7 This is true, and it's not just caused by evaporation. Air directly next to the skin is generally much warmer than room temperature (if ambient temp < body temp) which means that blowing air over the skin will replace warmer air with cooler air. This is why wind protection is important in cold weather; still air is an excellent thermal insulator, but it only works if you can actually prevent air next to the skin from flowing (which would otherwise quickly result in convective heat loss).
Born and living in a tropical, hot and humid country. I can confirm ventilator fans, or just moving air in general is really good for skin feel. I think slightly drafty indoors is something people living in temperate climates need to get used to and incorporate into their culture (global warming). I was so surprised when I holidayed in Europe and there were no fans (or air-conditioning) at all in the shared Airbnbs, it's fine in cold weather, but summer would be a broiling torture.
@@rabenklang7 Yes but the room wouldn't be cooler, thus it being subjective (subjective as in relation to the room - as "what/who is it impacting" and not the general room temp) For example, chinchillas don't sweat like us thus air flow does not cool them down. So cooling down the whole room is needed. (As opposed to just cooling you down)
I cant bloody sleep due to humidity for weeks, middle of night im wondering wtf to do, moving around the bed and furniture with this new science i learned, thankyou
came across this video today - fixed my poor ventilation for the last 1.5 years. even the box fan test helped me understand the difference in efficiency of design. thank you!!!
@@repentandbelieveinjesuschr9495 Matthew 4:10 "Away from me, Satan!" Jesus declared. "For it is written: 'Worship the Lord your God and serve Him only.'"
Fan placement really does make a difference. I live in the desert and it’s very hot here during summer. My ac is in a bad location in the house so I have to use fans to pull the cool air throughout the house. I have spent days and days moving fans around to find the perfect configuration for maximum cooling. One fan out of place and it will get hot, in the right place, I can stay 75 on a 100 degree day. There are a lot of factors and every home is different. Experiment with your fans! Move them all over the place, you will find the best spot. In the right location a fan on low can really help keep you cool.
I do the same experiment the problem is that I have a ceiling fan and it cannot be moved, so to have the better freshness I'm the person who has to move 😅
It's not as powerful as I thought it would be, but it works very well. ru-vid.comUgkxGjG43--gYqIoT4Xkur2PqCrtbKwTv2h6 There are three options to circulate air, and best of all a remote control for us lazy people. Installation was a breeze (no pun intended). It actually took longer to open the box then it did putting the side extenders on and sitting it in the window opening. It's a perfect alternative when you want airflow, but not the AC. Just might order another one for a different room. UPDATE: Bought another one like I said. They work great. Why not have two...
I was trying to figure out what's the best placement for fans just by using logic, but quickly realised it's a pretty tricky question and probably needs actuall testing. This video is highly apreciated!
there's loads of videos like this that are straight to the point, you only get 'commercialized' videos with 'spicy editing' because youtube looks at your watch history and gives you videos based on that. so if you don't want those kinds of videos stop viewing them.
I’d argue he says I’m bored all the time. Otherwise, why would he start to ponder optimal fan positioning and the need for actual science confirmation if he were already sufficiently stimulated.
I think there's two types of boredom: 1. "I'm bored nothing satisfies me" 2. "I'm bored, time to find some thing to do." The second one only lasts a moment.
Thank you for this. I have 1 pedestal fan and a floor fan and have been experimenting on how to get the greatest air flow in my house. Simply moving the pedestal fan 2.5 feet from the window and using it to vent has given me the best cross breeze I could ask for
A few years ago I built a fan with a tight enclosure to fit in a window, effectively sealing the window off. With only a few mm between the fanblades and the enclosure, it draws quite an airflow.
@@head85 PC cooler fan or similar, most likely. Those are the easiest to mount onto a wooden window insert, as they come with screw holes. You can even get larger models, e.g. 200mm instead of the most common 120mm, meaning you can spin them slower (reducing the noise) while moving more air.
@@EvenTheDogAgrees my fan (and it's "enclosure" (not sure how to translate it in English)) is built into a wooden insert, just as you described. The only difference is the fan itself. It's an industrial grade 230V fan of about 500mm (no typo) and draws well over 3000m³/h. 🤣 When it was still in use, I usually ran it at about 40% capacity to avoid complaints from my neighbours across the street 🤣 Trust me, I've been laughing my ass of after I turned it on for the first time. Up until then I just didn't have a single clue what it would be like to have a fan blowing 3000m³/h of air through my apartment 🤣🤣🤣
Today I was trying different positions for my fan as well because the air circulation in my room is horrible. Thats why Im very surprised that this gets suggested to me.
When I was a kid living in Austin, TX, we had no AC and brutal summers and we used fans for cooling... I’d turn the sheet on my bed into a diamond shape and tuck the corners under the mattress, leaving gaps on the straight pieces of top sheet, tie the foot end of the sheet to the handle of the box fan in the window, and turn the fan on. It blows up the sheet into a tent, circling the cool air around you (especially great at night), but the gaps allow some air to escape so the sheet won’t blow completely off the bed. TLDR; livin in the year 3000 back in 1978
Hi Matthias ! Last summer (July 2022) I did the same kind of experiment! And find about the same results. My fan was one of those tall 5' on a pedestal 18 inches blade. The best distance was about a meter and a half from the window. Since air acts like a liquid, one has to think outside the box. ( or outside the fan cage in this case) From what I gathered is that those fans dont pull air much from the back but they actually create a turbulence around the cage that pushes the flow instead of a coherent vortex. (like a turbine) I am happy to see that someone actually did a better scientific approach!
I'm trying to find one where the results include blocking the window off where the fan is. Blocking the edges so there's no leading back draft. Whenever I put a window in a fan I always block the unused portions of the screen off.
Finally a to the point test with clear testing and results without 5 ad breaks and sponsor shoutouts for testing the best plastic bag to paint your doors with. Thank you.
No joke, this guy proofed that I've done the right measurement for my room! I'm living in a very small room usually closing the door with only fan and not air-cond, the room temperature was really hot when the weather is hot and I tried to turn my fan towards living room with door opened, and it result in getting more cold air in my room instead! Thank you for doing this air circulating science stuff! I was so excited when I found that someone actually do this to collect data!
Had to comment again to express thanks, I've now shared this with numerous people who don't have A/C during the current round of heatwaves, so thanks so much for helping keep so many people cool!
@@Blernster wasting electricity, the cooled air isn't healthy and make headache and/or throath diseases, they're loud and need a lot of space... "genious"
I love the way you hooked up those devices and experimented with placement. I admire your skills! I’m watching this from England, where the weather is just warming up.👍
Hi sir. I want to thank you from the bottom of my heart! This tip solved a big issue for me and my family. We hated summer times because we had trouble sleeping in our apartment. I have a quite powerful AC which does the job, however it was drying the air too much and my little daughter was having trouble with her throat. We got quite a qood humidifier but it didn't do much. ... but man, this tip, I tried in and it made the temperatures ideal for sleeping without sweating. It's been 10 days since I implemented it and in all of them we slept without any issues! Thank you a million times and God bless you good sir!
Just coming back to say that this has made our lives better already. We've been using fans all wrong and this makes a massive difference. We can now be comfortable in our apartment on hot days and it feels amazing. Thank you, thank you, thank you.
I have spent a lot of time thinking about this problem but never felt the need to put much effort into it. Thank you for doing a proper experiment and putting it here for everyone to benefit
Tis video is amazing. I've been testing methods in my appartment for days now. The best one so far made for a slight breeze. This method had the 1 fan right up against a window. I decided to move it back about a meter and now i am blowing of my couch. Thank you so much
Believe it or not, I've discovered this about 2 years ago by accident, I was cleaning my room, and my intention was to pull the dust outside by putting my fan facing my opened door and about in the middle of the room. While cleaning I noticed that my room was getting cooler and cooler over time.
Love that you did the math.. I kind of reached same conclusion trying to move air from front door to back door, i.e. pushing at the backdoor at ~1meter distance seemed to do the most
This totally works, I saw several videos of this in the past and tried it myself. I didn't do all the air speed tests, but it changes it from taking an hour or more to cool my room with only a slight temperature change even when it's like in the 60s outside to bare minutes. Obviously the colder outside the faster and bigger the effect, but just the shear difference between having the fan in the window sill versus like 2-3 feet back made a huge difference in cooling my room. A whole house would be slower since it's a much greater volume of air that has to be moved but it would still have a much greater effect. My basic understanding of the reason is basically that by putting some space between you're increasing the volume of air from inside that can be pushed outside, that with the greater space more air will flow faster into that space than will just flow into the back of the fan.
We use this in the USA to ventilate houses in firefighting. Back the fan off the opening just enough to where the cone of moving air from the fan cobers the opening. You can take another fan, put it outside on the other side of the house and have it force air into the house. Again you want to back it away from the opening far enough for the cone of forced air to encompass the entire opening. Also, all other windows and outside doors have to be closed for it to work.
Did you think that sounded smart? It is obviously used to ventilate smoke AFTER the fire. I don't know if you were trying to sound funny with your comment or not, but instead you showed a clear lack of practical sense, and an aptitude for stupidity. There are other methods of ventilation used in active fire situations btw, but I don't think you would care to know by your comment.
Thanks for explaining it so well. Fellow firefighter here, can confirm this is how we ventilate a building. There's a lot of research on this so we see it as part of our training, and it is very interesting to see it work for yourself.
I have an outside generator shack that has to be ventilated when the generator is in operation. The ventilation is needful both to cool the inside of the shack (and thus the cooling air available to the engine) and to supply fresh air for the engine to use for combustion. I've been playing with/experimenting with fan placement trying to figure out how the best airflow is accomplished. Preferably without sucking exhaust fumes back inside the shack. The information in this video is very useful towards that end. I have no way to gauge the airflow in and out of the structure. Thank you for taking the time to put this together.
@@ateryx the idea of the scientific method is covered, but it's application in the real world is rarely talked about. we're just all suppose to "trust the experts" and if we use the internet in any way to get our information, it's faulty and "unofficial"
@@pinefilms3141 Maybe you slept in science class? It is definitely talked about and used in schools. Remember, research is only the FIRST STEP in the scientific method.
I have no ac in my home and every year I end up putting fans in different areas, and hoping it will keep me cooler than the year before. Now I know where to put them to be the most efficient! Thank you so much!
At first i did not believe this but gosh I couldn't believe when i started to feel the air circulation inside my room, thank you very much for your wonderful video, sending hugs and kisses from Philippines
@@mr_coffee0508 yes I live in Philippines, sadly I can't afford to buy aircon, so thid method really made a huge difference compared to not doing this technique
As many people have said, it seems to be a result of the flow of air pulling more adjacent air out the window along with it. I think this is the bernoulli's effect, which you can look up someone blowing up a large bag with air in one breath because of the same principle.
My favorite thing about this video is that each time I started thinking "but what about..." you jump in to adjust and account for it, throwing in a concise explanation as a bonus. So good!
@@hereandthere4751 I think it does work in both directions, since wind speed is a vector, it's just that it would spin backwards and maybe show up a negative reading
@@hereandthere4751 fan facing inwards does nothing for circulation cuz it can only suck in air that is right behind it and the wind it generates is immediately lost
I remember watching this video when it first came out. Was lucky enough to get recommended it out of nowhere. It was a nice change of pace. Now, I'm trying to setup some cross ventilation in my home and I kept thinking of this video. Everything comes around eventually.
Watched this when it was released and it just popped up again. Just wanted to say this was super useful at my last apartment and I think about this more often than I should 😂 Big thank you!
Years ago in a non-A/C house in MN I made a plenum that I could hang in the top sash area of a window and the box fan would set horizontal on the thin wooden plenum about a foot from the ceiling. That exhausted and pulled the hottest air from the ceiling and pushed it outside. Worked wonderfully. Better than any other implementation I tried.
@@matthiasrandomstuff2221 It actually looked nice. I made it look nice. Triangular cross section if looking from the side and guiding the air towards the window. This allowed me to walk by the window without hitting my head. Remembering now, it only fed and fit the top half of the top sash. Not that noticeable from the back yard. :
@@oscargr_ Thanks. It worked so well I used it for years. I could close the top sash without removing anything and it fit in place without any fasteners. I showed it to the people that bought that house from me and they chose to keep it.
That's the right way to ventilate. Hot air rises.Vent out the warm air near the ceiling so that cooler air can come in to replace the exhausted warm air. For the best result you need cross room ventilation.
I installed a large fan in the apex of our attic. Not only does it remove the hot air in the attic, it pulls the cool evening air into the house and cools every room down considerably. Attic fans work! 👍
I used to live in a house with a big extraction fan pointing into the attic. It was noisy but the breeze through the house felt great. Is your attic fan purpose built for being in an attic? Did you have to add any ducting or vents?
I put a solar power attic fan in my roof over the shop. Before the fan I monitored the temperature in the attic space with an indoor/outdoor thermometer. I kept the indoor unit in the shop and the outdoor unit I stuck in the attic. The temperature exceed 140F any day the ambient temp was over 85F. This made the ceiling of the shop which is insulated hot. After installing the fan the hottest is has been in the attic is 126F, so about 20 degrees cooler. I have noticed that the temperature in the shop stays about 5 degrees cooler than before the attic fan was installed. Solar powered so only works when the Sun is out but hey that's when it's hottest so it all works out.
@@nefariousyawn Yes the attic fan was purpose built for being in the attic. (30 inch diameter 4 blades) It came with a round cowling that installs in the apex. I removed the extant square vent that was built with the house and created a round hole that fit the cowling. I sealed everything and then mounted the fan. (the outside of the cowling has louvered vents that close when the fan isn't on.) I installed a wall mounted switch for the fan in the hallway underneath so that we can manually control the fan. It also has a thermostat that can automatically control the fan when attic temperatures exceed a set point. The fan is quiet and it has an oil port for lubrication which I oil every spring.
@@aloseman There are some arguments it doesn't pay to win, even if you are right. What Matthias could REALLY use is another person to replicate this so he could point to THAT video and the other person could point to HIS video so that way they aren't in as much trouble with their respective wives as if they had pointed to the video they made specifically to prove their spouses wrong. :P
Been doing this for years just on a hunch from my fluid dynamics days that it was probably better. Good to see some actual data! Thanks for sharing it.
Nice work, Matthias. Patton, a fan manufacturer, recommends this in the literature that came with a fan I bought several years ago. As you have found from experimentation, best air exhaust from the house is blowing out from a distance from the window. Their illustration appeared to suggest a column of air being blown from the fan out the window central to the window opening, and other air current being invited to join the column going out the window. A turbulent column inviting some surrounding laminar flow ambient air out with it, if you will. A larger net effect VS placing the fan right at the window opening and only getting the column of air exiting the window. I have found that effectiveness of this strategy varies somewhat by fan setting. If I don't want as much air flow through my place, I turn the fan to a lower speed, and air flow goes way down. Then I move the fan closer to the window and air flow recovers a bit. An interesting variation on your experiments might be to establish a baseline air flow with the fan right at the window at max fan speed, then see how much you can reduce the fan speed with optimized distance from the window, to achieve the same baseline flow rate.
This is what i needed! I have a really low ceiling in my room at second floor and the heat is agonizing, now i can circulate my room better. thank you👍
I love the fan research, we need more citizen science! Measuring air flow is one variable, but another important metric would be the change in temperature with different fan orientations.
There would be too many variables for anyone to apply the data to their own situation. This video is good because he measured a simple metric that anyone can understand and means something no matter what your situation is. The more air you move the better. For temperature It all depends on how hot it is outside and how hot it is inside and how many windows you have available and so on.
from experience if the outside temp is cooler than inside, if your using a fan the fastest way to cool the inside air is to blow outside cooler air in. blowing air out is very inificient in the same conditions for cooling.
My guess is there is a causal correlation between amount of air you can exchange and the delta between the two temps you are comparing (inside/outside air). Could probably work something out knowing those numbers. My guess is more air exchanged, the quicker the delta's converge.
The thing happening here is air multiplication, vector augmentation, or entrainment. It is used for very high volume pumps, like bilge pumps and the air pumps that instantly fill the emergency slide for planes.
Thanks, Matthias. Working from home on low budget and need this to see how will I vent welding fumes out. It suddenlty popped from my feed & had to click it.
I did this and can't believe someone proved my point when my family asked why my fans pointed towards outside like I'm an idiot. I feel a more comfortable temperature when it points outside rather than points it directly toward my face. Thank you sir.
@@dsouza2000 It depends on the setup. In a closed room, no, I just tried it and the temperature went up, but in a house with open windows, if the temperature is cooler outside, you'll gradually pull cooler air in and push the warmer air out.
@@shadyspades because it's more effective to blow the hot air outside when it's cooler (morning or evening). This is also used for example in computer cases when you can only have one fan. When it's hot with direct sunlight (late morning and afternoon) I keep all the windows shut
One big reason putting the fan far away from the window works better is because of the Venturi effect. When the air speeds through space, it creates a low pressure zone that pulls in more air around it.
I think the viscosity of the air pulls along more air as well. Don't quote me on this though since I'm not an expert. If someone else knows more about this, feel free to elaborate on it :D
@@flaco1010 Venturei effect and Bernoulli principle are pretty much the same thing, you can explain, mathematically, a Venturi effect model with Bernoulli's equation.
Agreed. In fact I was going to put the same thing in the comments but you apparently beat me to it. Also, wrt his video, not all fans suck air in from the outer front perimeter and blow it out from the center. I have a fan that doesn't do that. It depends on the design of the fan. As you said, it is still desirable to have the fan a certain distance within the area that you are trying to blow the air out of because of the Venturi effect. I believe those respirator pumps also utilize the Venturi effect to maximize airflow as well.
Great video!! I learned as a child when sleeping in my grandparents attic bedroom to pull air in one window with a fan and blow it out of the window on the opposite side of the room with a fan. I'm now 63 living in Florida and still the use this method often to move air through the house.
I always pointed the fan out the window to help air flow, not sure why done this, it just made more sense to me that way. Now I have the data to prove it! :D
Pointing a fan inward makes the fan increase the air pressure to get hot air out, pointing it out doesn't change the pressure outside to any appreciable degree.
Not going to lie this is one of those things that, to most people, might seem benign but it's really interesting. This is why ducting on fans is so helpful. Subbed.
You have done mankind a service. Thank you! Learned to blow out from my dad, and, dood, the huuuuge battles I've had with people (usually the SO) over blowing out vs blowing in. I only ever questioned the placement.
Nice analysis! I'm an airflow expert and run a WHF company. The best way to get max volume and velocity is to pull the air IN through windows via WHF installed centrally and at highest point in house. With a 2-1 ratio house sqr ft to CFM you will get 12-15 air exchanges per hour. Besides cooling effectively and saving money vs AC, it eliminates odors, viruses and contaminants of all kinds. For me the study that i need to to confirm, although i know what the results will be, is the amount of window opening to maximize the venturii effect at each window(max velocity). Less is more, but there is a sweet spot for each scenario/layout. I tell clients to play with it until they notice he max boost
Yes. I had a difficult apt where no room opened to the next room. One level/top floor and hot. I had 3 whole house window fans and played with how much and which other windows to open in this scenario -- because the fans in different rooms couldn't communicate with each other. I found that cracking the top of window #1 in a line of 3 window with the WH window fan in the bottom portion of window 1 worked best.
Are you sure it reduces bacteria? We've done lab work on agar dishes exposed to outside air versus inside air and the bacteria growth was easily 10x more after 7 days of incubation for the outside air.
@@Nessal83 yea I’m pretty sure as are the WHF manufacturers and I think the EPA. Still that would be a good field test: test agar samples INDOORS with OUTSIDE air being drawn in over a number of hours/days
The reason why the fan being a little bit further away makes it more effective is know as Bernoulli's principle, which states that the pressure in a stream of fluid is reduced as the speed of the flow is increased. This is used in hydrodynamics but also applies to the air in the room with a window, as shown here
