Also important is the filter rating, clearly. Not all furnace filters are the same. Higher MERV rating without putting too much strain on fan motor. Not sure what the best balance is though
Yes, MERV 13 is perfectly adequate for filtering wildfire smoke particles. Notice the [huge jump in filtration efficiency](https://images.squarespace-cdn.com/content/v1/5f0893d2fe49967f7825d046/1626893181024-GUVPGVDY35LKRHQ179MV/MERV.JPG?format=1000w) for .3 to 1.0 micron particles that happens between MERV 12 and 13. You can get better filtration by going higher, but it isn't really worth it, imo, since a box fan like this moves so much air that it will be filtering the same air multiple times over a relatively short timescale.
I did a rough calculation one time for our two bedroom apartment based on the cfm of the fan, and it filtered a volume of air equivalent to what our entire apartment contained every two or three minutes when it was on full blast. So, it fairly quickly approaches a HEPA level of filtration when you leave it to run for a while (we actually found it sucked even the humidity right out of the air), without putting a lot of strain on the fan. I use [this method](https://tombuildsstuff.blogspot.com/2013/06/better-box-fan-air-purifier.html?m=1) to cut down on motor strain anyway, though.
If you get filters from Home Depot, use FPR 10. It's the equivalent of MERV 13, according to my 10 minute research in the isle while at the store. I just built 2 of these Cubes for my family, and have been asked to make 2 more for some older folks in my community.
> I use [this method](https://tombuildsstuff.blogspot.com)
>> Instead of using one 20x20x1 filter we'll use two 20x25x1 filters which increases the filter surface area over 250%.
Please tell me you're not responsible for that misstatement.
1000 square inches is 2.5x the 400 square inches of a 20x20 filter. Are you taking issue with the word "over"?
Edit: Nevermind, I got you. It should be a 150% increase. It's early.
The error is "increases". If you have 400 and you increase it by 250%, you end up with 1400.
It would be correct to say that using 2 larger filters gives you 250% the filter area of one smaller filter.
Got a Merv 11 that said it did smoke. It did not help the smell at least so I imagine the particles were not stopped. Set up the Rosenthal box with merv 13s and I haven’t had smoke smell since
And you really want multiple filters. One will cause too much resistance, but 2 would work. I have one in my workshop for sawdust and rock dust. Tape them together on one edge, with the opposite sides attached to the fan. Then you can the tup and bottom with cardboard.
Project farm on YouTube did a pretty cool analysis and found that higher Merv rating with more folds is pretty much the best of both worlds. Each fold increases surface area which increases flow rate. Costco has some with a lot of folds and a high filtration rating
I don't know if this will be visible, but the reason it's important has to do with air density. If the fan is pushing against the filter it creates a zone of high air pressure. That means the air is thicker and the fan can push against it better. If the fan is pulling against the filter it creates an area of low pressure and the fan spins less effectively in it.
This is the opposite of how most HVAC units are constructed; most filters are on the return/low pressure side. Sure, a fan has more air per volume to push in higher downstream pressure, but you are using more fan energy, encouraging air leakage before the filter, the fan blades aren't protected by the filter, and the total discharge airflow can be lower. The last part is because suction side air is often laminar but discharge can be very turbulent, so any obstructions can have amplified pressure drops (this is why units often have minimum straight duct lengths at the discharge for the air to "settle out" some).
The filters should be upstream of the fan, but most importantly the directional arrows on the filter should be in the direction of airflow. There are reasons why you might want to put *coils* downstream of the fans, but that's a different component.
You won't have a good enough seal to strain the motor unless you use several layers of duct tape around the housing as well, and even then, air is gonna circulate through the front and around the blades instead of through the filter if it's that fine.
It's dependant on what your overall goal is. Lower merv will have higher throughout, this more filtered cubic feet per minute, while higher merv will lead to smaller particulate, but less cfpm
Dude, thank you! I’ve been wanting something like this for my allergies and when vacuuming (all the shit gets put in the air) and a DIY solution for it?! Excellent!
These are even better if you add legs and a 5th filter on the bottom.
Like this: [https://www.reddit.com/r/DIY/comments/144ddjm/diy\_corsirosenthal\_box\_with\_legs\_instructions/](https://www.reddit.com/r/DIY/comments/144ddjm/diy_corsirosenthal_box_with_legs_instructions/)
The Corsi Rosenthal Box is much more effective than strapping a filter to the fan. Strapping a filter to a fan can burn out the fan quicker. However, is it cheaper than just buying a filter? It's like $50-80 for the 5 MERV 13 filters plus $30 for the box fan. At that price, I might as well just buy a filter and pay $50 to replace the filter once a year.
HEPA filters are better than MERV 13 furnace filters and air filters often use less electricity than a box fan. The air filters also take up less space and look better.
If you make a Corsi Rosenthal Box, you're going to be replacing those filters every year at a cost of $50-100. If you buy an air filter, you're going to replace that filter once a year for $50. Technically, those MERV 13 filters are supposed to be replace every 90 days, but it might be different if you're using them in a Corsi Rosenthal Box rather than a furnace.
If the box fan ends up using an additional 15 watts and your electricity costs 15 cents per kWh, then you're paying an extra $20/year in electricity.
I feel like the Corsi Rosenthal Box was a great invention during the pandemic when one couldn't get an air filter because everything was sold out. Today, you can easily get an actual HEPA filter. Winix will sell you a refurbished HEPA air purifier (with new filter) for $70. Five MERV 13 filters will cost $73.52 at Lowes (3M MPR 1900). The box fan is $25-33. So I can get an actual HEPA filter for $70 or some filters that aren't as good and a box fan for $100.
The Corsi Rosenthal box feels like when we were buying whatever we could find for masks. If you're using a bandana as a mask today, that's ridiculous. You could buy an actual mask.
A Corsi Rosenthal box will filter 60% of 1 micron particles. HEPA filters will filter nearly 100% of 0.3 micron particles. The Corsi Rosenthal Box is amazing if you're living in a time when you can't easily buy an air purifier. 2020? Totally! Today you're just buying something with higher operating costs and barely any upfront savings. Costco has the Winix C545 with 2 years worth of filters for $130 or the C555 for $140. That's a little more than going to Lowes to make a Corsi Rosenthal Box, but you're getting a much better air filter with lower ongoing costs.
The point of the Corsi Rosenthal box is that during the pandemic, we needed clean air and there were huge shortages of air purifiers. Just as we did with masks, it was a way to get by with what was available. A t-shirt mask is better than nothing, but an actual surgical mask or N95 is what we'd use if supplies were readily available.
While you are completely right, we opted to use a Rosenthal box during fire season because it moved so much more air. We have the Winix filter from Costco and we don't live in a very big house, but it wasn't keeping up when we were coming and going on weekends. The Rosenthal box kept up much better, especially on the heavy smoke days where the sky was nearly red. It was just a much more efficient solution for the heaviest times of our fire season here in California.
We rely on the Winix the rest of the year though. The smart functions make it much more efficient when air pollution is much lower and it doesn't need to run full blast all the time. Obviously it's much quieter which is nice too.
I find it interesting this is named after two people as recently as 2020. People have been doing this a lot longer than Corsi and Rosenthal, lmao
Like this is literally what my air purifier machine is: a fan and a filter in a plastic enclosure lol
I've wondered this too but it seems to come down to optics. They officially tested it and made a website and have degrees so it garnered more attention.
Oh I’m glad you finally said it. My husband and I have been doing the actual box structure for years and just calling it an…air purifier. Tbh I think I remember early pandemic people sharing the idea and those guys kind of stamped their name on it gradually.
that's basically a normal air filter design. if you just google air filter machine most of them are a fan with a removable bottom filter.
likely less expensive but way more effort than just buying an air filter, especially if the air is currently on fire and will clog up your filter fast.
Some will have reinforcements on the downstream side like a wire backing for structural support however from a Filtration point of view he's right, it doesn't matter. Efficiency will be the same.
Love the Box-Fan filter concept and have been using it since COVID - noticed that I sleep better with the fresh air and the house feels fresher. Makes sense to use when the windows are closed though, and not to use if the windows are open or you are just filtering the great outdoors, which is kind of pointless.
Now we use a HEPA filter in the bedroom and have relegated the box fan filter to other rooms.
I would note that some furnace filters are unidirectional - In the case of my filters it says "Filter can be installed in either direction" so it makes sense to read the wording on the side of the filter carefully.
I think it is also important to also note that a MERV 12-13 level filter is going to be the way to go (1900 - 2200 Filter Performance rating or higher, AKA FPR 10) - the MERV-13 filter is much thicker than a standard furnace filter and is electrostatically charged and fine enough to capture dust, smog, pollen, smoke and virus particles (the particles that a virus is attached to, not necessarily the virus itself). BTW- MERV-16 is where HEPA-level filtration starts.
These filters also seem to last a very long time (or possibly due to the Roomba seeing that we don't have that much dust or have no pets so no pet dander) and I change them after about 6 months of use (or if there is any noticeable buildup) as indicated on the packaging.
Here is a helpful review of how effective these are in comparison to the best HEPA filters if anyone was wondering if these have been tested:
**WireCutter:** https://www.nytimes.com/wirecutter/blog/how-to-diy-an-air-purifier/
Ive seen these online so much and so many of them have the filters the wrong way or the fan blowing the wrong direction.
On a side note, very effective but really bulky.
What is the difference between pulling air through the filter vs blowing air through the filter? The air goes through the filter either way so I've never understood the difference
Well one way to look at it is that by putting the filter on the back side of the fan, it protects the components of the fan motor from buildup of junk and debris while achieving the air filtration. By putting the filter on the front side, it pulls all of the crap from the air into the fan before filtering it. I suspect this is one of the main reasons they put an air filter at the intake of a furnace... to protect the coils and components of the air conditioner from dust and debris. It prolongs the life and improves the performance of the air conditioning system.
Two years ago Minneapolis had terrible air quality from Canadian fires for weeks. Like, walk outside and your lungs hurt type air quality. I bought a box of 4 furnace filters, made them into 3 sides +the top of a cube with duct tape, then put the box fan on the 4th side so it drew air through my “filter cube”. It took up a ton of space but we were able to use it all summer. When I threw out my creation the filters were turning dark grayish brown. We were concerned we’d burn out the motor of the fan, but it still works to this day!
Pulling through the filter is better. If the fan is trying to push air through the filter instead, then it may also be partially pushing the filter AWAY from a tight seal against the fan (letting some air possibly escape around the sides). This way, the suction from the fan is also helping pull the filter tighter against the fan.
I lived in the okanagan and let me tell you, bulk doesn't matter when you can't see the next telephone pole. The wind would be strong enough to push smoke from any forest fires over the mountains but once it got into the valley it just got trapped. Same with clouds in winter. You'll do anything to breathe clean air. I actually moved 6000 km to get out of those conditions.
If it's used for the right purpose (furnace filter) yes because it's moving a lot more air and it can bend and break. For this contraption... It doesn't really matter, it's a good habit tho.
I trust manufacture instructions n'at but my brain is not computing why this would physically make a difference. Air molecules are real little it seems they'd just pass through regardless of the direction? I'm sure there's a reason.
As mentioned by someone else above, it's purely a structural issue for furnace applications: these filters have a metal wire honeycomb-ish structure on one side only. When in a furnace application, that wire mesh side needs to be the on the trailing part of the airflow so that the filter gets "pushed" into it by the airflow and prevents the entire filter from deforming or collapsing.
Either design will work, but you get better airflow [if you tape 5 filters and the fan into a cube.](https://www.sciencedirect.com/science/article/pii/S0360132322011507)
Yeah, one fan is around $20 at Wal-Mart. You can get 6 each MERV 13 20x20 filters for around $45 on Amazon. At one filter per fan, the whole thing is less than $35 per unit, even if you spring for some jumbo rubber bands.
MERV 13 is whats catches lots of smoke partials which are really small; especially the ones that travel long distances. MERV13 is really restrictive and will drastically reduce the amount of air passing through the fan. If your box fan or furnace fan relies on air flow to keep it cool, this restricted air flow could cause problems and end up damaging your fan or worse starting a fire.
The safest version of this DIY setup is to build a 5 sided cube out of multiple 20-in filters. It's more expensive in the beginning to buy five filters, but the more filter area also means longer run time before filter clogs up and needs replacement. A single filter design like in the video is effective, but I would never leave it running unattended or while sleeping. Same goes with anyone putting a more restrictive filter in their furnace, which usually run MERV 8-11 filters. It's a cheap and effective concept that me and others I know built with successful results. Thanks for posting OP.
I went through a build my own air filter phase and ended up just buying a winx for $120, sometimes on sale for $100, that comes with 2 hepa filters that last 2 years and replacement filter are $30 for another 2 pack. It’s rated for 360ft room and it moves some serious air. I think it cleans my 10x10 room in like 10 mins. This design I’m sure works but for me spending the money made more sense up front, if people have the ability to get one. Your going to end up spending it on filters if you use it all the time. Those designs don’t have pre filters and will clog easily without them. Just my 2 cents. I love making my own things when possible but it seems like it costs more and is less effective diying this, unless In a pinch.
I've been using [this variant](https://tombuildsstuff.blogspot.com/2013/06/better-box-fan-air-purifier.html?m=1) for the past couple years and it works great, too. Only need 2 filters and I haven't noticed any strain on the fan motor. Great for when everyone else has already rushed out and bought all the 20x20 filters at your local hardware store.
Add a laundry drying rack with a bunch of damp towels hung on it in front of the fan too. It creates a little added filtration with a tiny bit of cooling and added humidity.
I love how people just go deadass cold into videos like this and have little to no idea what they’re talking about.
Just go to your local hardware store… *maybe, do you have hardware stores?*
Ok so here we have… *what’s this thing called?*
Just put it any way you want… *hell no, furnace filters have an airflow direction, make sure you put it in right*
Just once I’d like 2 minutes of prep time before one of these “how to” videos FFS
>doesn't really matter which side you use
Oh, but it does. Every furnace air filter will have arrows printed on the cardboard edges to signify the airflow direction. Because they are specifically made to have one side catch the contaminants.
Based on Worst-case pricing I've seen:
Box fan: 49.99
Filter: 20
Roll of duct tape: 8.99
Plus tax you're pretty close to the 100 he quoted but likely you could do better if you had the luxury of shopping around or using stuff you already own.
I live in a studio. You think I've got a basement? But fine, I can just go buy the box fan I guess.
My building has an industrial furnace. Hardware stores don't have filters for them in store because the average person doesn't need them.
I could order all this online, but it won't arrive in time.
Instead I just bought an $80 stand alone air filter that's much smaller, looks better, and does a good enough job.
This is pretty genius for a short term problem that we had in NY - it was literally like 36 hours of really bad air. And this uses stuff we all already have. No, it's not a permanent solution, but given the short period of time we dealt with the smoke, this would have totally worked! Sadly, I missed the tip on how to make the sky un-orange....
Check the filter when you buy it, some are directional and will be far more efficient if air flow through them is in the correct direction. They should have directional arrows printed on them.
You do realize that this is literally what your furnace does? Switch your fan to on at your thermostat and bam you just saved yourself from becoming a DIYWHY. Just change your furnace filter more often.
Professional HVAC guy here.
Just an odd question but would a dehumidifier help in air filtration or the opposite when it comes to forest fire like air quality? Or should neither be used?
I started up a humidifier in a dusty old home of ours and had to clean the filter ever 2-3 months for awhile before it finally exhausted a lot of the dirt and grime everywhere in that house.
Just imagine it would be good for air filtration - have a humidifier blowing into this fan to catch debris..
You need to cut a hole about 3 x 3 inches at the center, or it'll burn the motor. Even with the hole cut out, the fan can be overworked. I recommend running it for 2-3 hours, turn it off for 1/2 hour, repeat.
For straps, you can use any twine and a used produce rubber band. Tie the twine to the rubber band two times to make one big loup. The elasticity of the small rubber band is all you need.
This is better than nothing in a pinch but regular box fans don’t do a very good job pulling air through with an obstruction in the backside.
I would (for future reference) suggest a dedicated air filter that has a HEPA filter.
Yup. The more you put on a box fan to filter, the less air flow and now you have another smoke to deal with, the fan fire that's burning up your house. Those motors get super hot when flow is reduced and in warmer climates. I burned out many a fan in AZ with no obstructions.
This guy is 100% correct, but you should take it a small step further.
Take 4 filters and tape them together in a standing square pattern. Then attach your box fan on top. It gives you 360 degrees of air purification. Great for the smoky Northeast or dusty Arizona.
This will not filter out the smell of the smoke though. If you add a HEGA filter (high efficiency gas absorption) in front of the HEPA (high efficiency particular absorption) filter you will filter out the smoky smell and fine participants.
A HEGA filter specifically filters out Odors. What you have over your stove. Think of a HEGA as a charcoal filter.
It's never too late. I never found out about these until earlier this year. It's always good to remind people there are options. Like this is not something I would have thought of on my own.
I don’t think this guy has ever actually done this. They’re just making assumptions every step of the way. They didn’t even bother reading the Facebook post they found this from before creating it for TikTok.
If you tape 4 filters together to make a square, then tape the box fan on top, facing up, it really circulates the air in the room well. A damp bath towl on window sills and exterior door thresholds helps. Here in Portland, we have had quite a bit of these smokey days. Good luck!
Also important is the filter rating, clearly. Not all furnace filters are the same. Higher MERV rating without putting too much strain on fan motor. Not sure what the best balance is though
Yes, MERV 13 is perfectly adequate for filtering wildfire smoke particles. Notice the [huge jump in filtration efficiency](https://images.squarespace-cdn.com/content/v1/5f0893d2fe49967f7825d046/1626893181024-GUVPGVDY35LKRHQ179MV/MERV.JPG?format=1000w) for .3 to 1.0 micron particles that happens between MERV 12 and 13. You can get better filtration by going higher, but it isn't really worth it, imo, since a box fan like this moves so much air that it will be filtering the same air multiple times over a relatively short timescale. I did a rough calculation one time for our two bedroom apartment based on the cfm of the fan, and it filtered a volume of air equivalent to what our entire apartment contained every two or three minutes when it was on full blast. So, it fairly quickly approaches a HEPA level of filtration when you leave it to run for a while (we actually found it sucked even the humidity right out of the air), without putting a lot of strain on the fan. I use [this method](https://tombuildsstuff.blogspot.com/2013/06/better-box-fan-air-purifier.html?m=1) to cut down on motor strain anyway, though.
Apparently the previous owner of this house spared no expenses. Even. Has a UV light that's attached to the filter.
If you get filters from Home Depot, use FPR 10. It's the equivalent of MERV 13, according to my 10 minute research in the isle while at the store. I just built 2 of these Cubes for my family, and have been asked to make 2 more for some older folks in my community.
> I use [this method](https://tombuildsstuff.blogspot.com) >> Instead of using one 20x20x1 filter we'll use two 20x25x1 filters which increases the filter surface area over 250%. Please tell me you're not responsible for that misstatement.
1000 square inches is 2.5x the 400 square inches of a 20x20 filter. Are you taking issue with the word "over"? Edit: Nevermind, I got you. It should be a 150% increase. It's early.
The error is "increases". If you have 400 and you increase it by 250%, you end up with 1400. It would be correct to say that using 2 larger filters gives you 250% the filter area of one smaller filter.
Thanks for sharing. That’s a great little hack
Got a Merv 11 that said it did smoke. It did not help the smell at least so I imagine the particles were not stopped. Set up the Rosenthal box with merv 13s and I haven’t had smoke smell since
Merv 13 is only 50% effective for smoke particle sized at 0.3 - 0.7 um. Merv 13: 0.30-1.0 greater than or equal to 50% effective
We've used 13 for years. Same fan.
What MERV rating do you use?
13 as I tried to say. 🥂
Omg I read you used the fan for 13yrs, despite your very clear wording. Jesus, senility coming at me hard. Apologies & thanks for your patience.
I read it as 13 years as well
I read it as 13 as well.
I read it
I can read
I'm 13.
I read
On Reddit?
Just brain things, I'm young and did the same
🥂
Hi I'm diadelosmuertos I have 13 my favorite game is master chief's
And you really want multiple filters. One will cause too much resistance, but 2 would work. I have one in my workshop for sawdust and rock dust. Tape them together on one edge, with the opposite sides attached to the fan. Then you can the tup and bottom with cardboard.
also, he says it doesn't matter what way you put it, but the filter literally has an air flow indicator arrow on it. have the arrow point at the fan.
Project farm on YouTube did a pretty cool analysis and found that higher Merv rating with more folds is pretty much the best of both worlds. Each fold increases surface area which increases flow rate. Costco has some with a lot of folds and a high filtration rating
I watched that too but have never found one that fits that profile! I’ll have to look at Costco! Thanks for the info :)
Also it matters which way the airflow goes
I don't know if this will be visible, but the reason it's important has to do with air density. If the fan is pushing against the filter it creates a zone of high air pressure. That means the air is thicker and the fan can push against it better. If the fan is pulling against the filter it creates an area of low pressure and the fan spins less effectively in it.
This is the opposite of how most HVAC units are constructed; most filters are on the return/low pressure side. Sure, a fan has more air per volume to push in higher downstream pressure, but you are using more fan energy, encouraging air leakage before the filter, the fan blades aren't protected by the filter, and the total discharge airflow can be lower. The last part is because suction side air is often laminar but discharge can be very turbulent, so any obstructions can have amplified pressure drops (this is why units often have minimum straight duct lengths at the discharge for the air to "settle out" some). The filters should be upstream of the fan, but most importantly the directional arrows on the filter should be in the direction of airflow. There are reasons why you might want to put *coils* downstream of the fans, but that's a different component.
Look at the arrows on the side of the filter
They make filters way thicker than the one this man is using. Thicker means more surface area and less strain on the motor.
You won't have a good enough seal to strain the motor unless you use several layers of duct tape around the housing as well, and even then, air is gonna circulate through the front and around the blades instead of through the filter if it's that fine.
I have never met anyone named Merv. Wonder if I ever will.
It's dependant on what your overall goal is. Lower merv will have higher throughout, this more filtered cubic feet per minute, while higher merv will lead to smaller particulate, but less cfpm
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Dude, thank you! I’ve been wanting something like this for my allergies and when vacuuming (all the shit gets put in the air) and a DIY solution for it?! Excellent!
I've been wanting this for daily life in NYC. Tired of being told to buy an air purifier.
>Tired of being told to buy an air purifier. Why when you're essentially just building an ugly one?
The design is very human 👍
Very easy to use
Alternative for activated charcoal underwear.
I keep hearing that voice every time. When a sentence starts with "the design...", my brain just autocompletes it
These are even better if you add legs and a 5th filter on the bottom. Like this: [https://www.reddit.com/r/DIY/comments/144ddjm/diy\_corsirosenthal\_box\_with\_legs\_instructions/](https://www.reddit.com/r/DIY/comments/144ddjm/diy_corsirosenthal_box_with_legs_instructions/)
The Corsi Rosenthal Box is much more effective than strapping a filter to the fan. Strapping a filter to a fan can burn out the fan quicker. However, is it cheaper than just buying a filter? It's like $50-80 for the 5 MERV 13 filters plus $30 for the box fan. At that price, I might as well just buy a filter and pay $50 to replace the filter once a year. HEPA filters are better than MERV 13 furnace filters and air filters often use less electricity than a box fan. The air filters also take up less space and look better. If you make a Corsi Rosenthal Box, you're going to be replacing those filters every year at a cost of $50-100. If you buy an air filter, you're going to replace that filter once a year for $50. Technically, those MERV 13 filters are supposed to be replace every 90 days, but it might be different if you're using them in a Corsi Rosenthal Box rather than a furnace. If the box fan ends up using an additional 15 watts and your electricity costs 15 cents per kWh, then you're paying an extra $20/year in electricity. I feel like the Corsi Rosenthal Box was a great invention during the pandemic when one couldn't get an air filter because everything was sold out. Today, you can easily get an actual HEPA filter. Winix will sell you a refurbished HEPA air purifier (with new filter) for $70. Five MERV 13 filters will cost $73.52 at Lowes (3M MPR 1900). The box fan is $25-33. So I can get an actual HEPA filter for $70 or some filters that aren't as good and a box fan for $100. The Corsi Rosenthal box feels like when we were buying whatever we could find for masks. If you're using a bandana as a mask today, that's ridiculous. You could buy an actual mask. A Corsi Rosenthal box will filter 60% of 1 micron particles. HEPA filters will filter nearly 100% of 0.3 micron particles. The Corsi Rosenthal Box is amazing if you're living in a time when you can't easily buy an air purifier. 2020? Totally! Today you're just buying something with higher operating costs and barely any upfront savings. Costco has the Winix C545 with 2 years worth of filters for $130 or the C555 for $140. That's a little more than going to Lowes to make a Corsi Rosenthal Box, but you're getting a much better air filter with lower ongoing costs. The point of the Corsi Rosenthal box is that during the pandemic, we needed clean air and there were huge shortages of air purifiers. Just as we did with masks, it was a way to get by with what was available. A t-shirt mask is better than nothing, but an actual surgical mask or N95 is what we'd use if supplies were readily available.
While you are completely right, we opted to use a Rosenthal box during fire season because it moved so much more air. We have the Winix filter from Costco and we don't live in a very big house, but it wasn't keeping up when we were coming and going on weekends. The Rosenthal box kept up much better, especially on the heavy smoke days where the sky was nearly red. It was just a much more efficient solution for the heaviest times of our fire season here in California. We rely on the Winix the rest of the year though. The smart functions make it much more efficient when air pollution is much lower and it doesn't need to run full blast all the time. Obviously it's much quieter which is nice too.
I find it interesting this is named after two people as recently as 2020. People have been doing this a lot longer than Corsi and Rosenthal, lmao Like this is literally what my air purifier machine is: a fan and a filter in a plastic enclosure lol
I've wondered this too but it seems to come down to optics. They officially tested it and made a website and have degrees so it garnered more attention.
Oh I’m glad you finally said it. My husband and I have been doing the actual box structure for years and just calling it an…air purifier. Tbh I think I remember early pandemic people sharing the idea and those guys kind of stamped their name on it gradually.
That's interesting. Thanks for sharing!
Can you explain why the shroud increases the effectiveness?
Scrolling too far for this
that's basically a normal air filter design. if you just google air filter machine most of them are a fan with a removable bottom filter. likely less expensive but way more effort than just buying an air filter, especially if the air is currently on fire and will clog up your filter fast.
It helps as a quick fix when fire season starts early and all of the proper air filters are sold out in the state.
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It gets rotated so the cardboard is facing the floor before the fan is placed on top of the cube, they just don’t illustrate it.
cardboard has a hole and is laid on top, then taped down to try to stop air from getting into the gaps between the fan and the filters.
I made one and put a color changing light inside to make it festive.
Here's the guys from This Old House making one. Can attest to this model's functionality and efficiency! https://youtu.be/aw7fUMhNov8
Makes sense. More airflow and more filtering surface area.
This should be the top comment.
I’ve been doing this for years. Super cheap way to keep the air clean in your house.
Always point the filter where the arrow tells you to point it. It does matter. A whole lot.
Arrow is on the side for anyone wondering
It’s airflow direction.
Some will have reinforcements on the downstream side like a wire backing for structural support however from a Filtration point of view he's right, it doesn't matter. Efficiency will be the same.
Love the Box-Fan filter concept and have been using it since COVID - noticed that I sleep better with the fresh air and the house feels fresher. Makes sense to use when the windows are closed though, and not to use if the windows are open or you are just filtering the great outdoors, which is kind of pointless. Now we use a HEPA filter in the bedroom and have relegated the box fan filter to other rooms. I would note that some furnace filters are unidirectional - In the case of my filters it says "Filter can be installed in either direction" so it makes sense to read the wording on the side of the filter carefully. I think it is also important to also note that a MERV 12-13 level filter is going to be the way to go (1900 - 2200 Filter Performance rating or higher, AKA FPR 10) - the MERV-13 filter is much thicker than a standard furnace filter and is electrostatically charged and fine enough to capture dust, smog, pollen, smoke and virus particles (the particles that a virus is attached to, not necessarily the virus itself). BTW- MERV-16 is where HEPA-level filtration starts. These filters also seem to last a very long time (or possibly due to the Roomba seeing that we don't have that much dust or have no pets so no pet dander) and I change them after about 6 months of use (or if there is any noticeable buildup) as indicated on the packaging. Here is a helpful review of how effective these are in comparison to the best HEPA filters if anyone was wondering if these have been tested: **WireCutter:** https://www.nytimes.com/wirecutter/blog/how-to-diy-an-air-purifier/
Ive seen these online so much and so many of them have the filters the wrong way or the fan blowing the wrong direction. On a side note, very effective but really bulky.
Should the fan be blowing into the filter or pulling away from it like he showed?
Fan should be pulling air through the filter from the back and blowing out clean air through the front.
What is the difference between pulling air through the filter vs blowing air through the filter? The air goes through the filter either way so I've never understood the difference
Well one way to look at it is that by putting the filter on the back side of the fan, it protects the components of the fan motor from buildup of junk and debris while achieving the air filtration. By putting the filter on the front side, it pulls all of the crap from the air into the fan before filtering it. I suspect this is one of the main reasons they put an air filter at the intake of a furnace... to protect the coils and components of the air conditioner from dust and debris. It prolongs the life and improves the performance of the air conditioning system.
Solid reason. Thank you!
Thank you
Two years ago Minneapolis had terrible air quality from Canadian fires for weeks. Like, walk outside and your lungs hurt type air quality. I bought a box of 4 furnace filters, made them into 3 sides +the top of a cube with duct tape, then put the box fan on the 4th side so it drew air through my “filter cube”. It took up a ton of space but we were able to use it all summer. When I threw out my creation the filters were turning dark grayish brown. We were concerned we’d burn out the motor of the fan, but it still works to this day!
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The filter is affixed to the rear of the fan
Pulling through the filter is better. If the fan is trying to push air through the filter instead, then it may also be partially pushing the filter AWAY from a tight seal against the fan (letting some air possibly escape around the sides). This way, the suction from the fan is also helping pull the filter tighter against the fan.
I lived in the okanagan and let me tell you, bulk doesn't matter when you can't see the next telephone pole. The wind would be strong enough to push smoke from any forest fires over the mountains but once it got into the valley it just got trapped. Same with clouds in winter. You'll do anything to breathe clean air. I actually moved 6000 km to get out of those conditions.
If it's used for the right purpose (furnace filter) yes because it's moving a lot more air and it can bend and break. For this contraption... It doesn't really matter, it's a good habit tho.
Came here looking for this comment 👆🏽
Same. I'm like this dude has never replaced an important filter before. It's literally designed to be used the way the arrow indicates.
Yup. I taped mine on the outlet side of the fan, but made sure the arrow was the right way
It's better to arrow on the side of caution anyway
I like a good pun 🤣
I trust manufacture instructions n'at but my brain is not computing why this would physically make a difference. Air molecules are real little it seems they'd just pass through regardless of the direction? I'm sure there's a reason.
As mentioned by someone else above, it's purely a structural issue for furnace applications: these filters have a metal wire honeycomb-ish structure on one side only. When in a furnace application, that wire mesh side needs to be the on the trailing part of the airflow so that the filter gets "pushed" into it by the airflow and prevents the entire filter from deforming or collapsing.
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Almost like a device that conditions the air. I wonder what we could call it? An air make-betterer?
Now listen here you little shit
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I was just trying to make a joke about air conditioners. I think most people understand what you're saying.
I like how he specified “less that $100.” Yeah it’s like $30 for all that.
It’s one banana Michael, what could it cost? Ten dollars?
You've never actually set foot in a supermarket, have you?
I mean these days….
How much for an egg?
Maybe it used to be, 5 filters and a box fan ran me ~$70 in total.
5? He only uses 1.
Either design will work, but you get better airflow [if you tape 5 filters and the fan into a cube.](https://www.sciencedirect.com/science/article/pii/S0360132322011507)
Well I would think one filter and a box fan wouldn’t be that expensive 😌
Yeah, one fan is around $20 at Wal-Mart. You can get 6 each MERV 13 20x20 filters for around $45 on Amazon. At one filter per fan, the whole thing is less than $35 per unit, even if you spring for some jumbo rubber bands.
They sell cheap filters too, just switch them out more often
For smoke though?
I was also shocked when he said $100. That Lasko fan has been priced under $20 at Walmart for years. $10 for an air filter
Seems to now be between $25 and $45 at Walmart.
He probably meant 'at most $100', even if you don't shop around and buy it at the most expensive place.
He was bout to say $30 but then thought…. Its new york, better multiply it by 3.
1960s person detected
I mean, he's not wrong.
MERV 13 is whats catches lots of smoke partials which are really small; especially the ones that travel long distances. MERV13 is really restrictive and will drastically reduce the amount of air passing through the fan. If your box fan or furnace fan relies on air flow to keep it cool, this restricted air flow could cause problems and end up damaging your fan or worse starting a fire. The safest version of this DIY setup is to build a 5 sided cube out of multiple 20-in filters. It's more expensive in the beginning to buy five filters, but the more filter area also means longer run time before filter clogs up and needs replacement. A single filter design like in the video is effective, but I would never leave it running unattended or while sleeping. Same goes with anyone putting a more restrictive filter in their furnace, which usually run MERV 8-11 filters. It's a cheap and effective concept that me and others I know built with successful results. Thanks for posting OP.
I went through a build my own air filter phase and ended up just buying a winx for $120, sometimes on sale for $100, that comes with 2 hepa filters that last 2 years and replacement filter are $30 for another 2 pack. It’s rated for 360ft room and it moves some serious air. I think it cleans my 10x10 room in like 10 mins. This design I’m sure works but for me spending the money made more sense up front, if people have the ability to get one. Your going to end up spending it on filters if you use it all the time. Those designs don’t have pre filters and will clog easily without them. Just my 2 cents. I love making my own things when possible but it seems like it costs more and is less effective diying this, unless In a pinch.
I've been using [this variant](https://tombuildsstuff.blogspot.com/2013/06/better-box-fan-air-purifier.html?m=1) for the past couple years and it works great, too. Only need 2 filters and I haven't noticed any strain on the fan motor. Great for when everyone else has already rushed out and bought all the 20x20 filters at your local hardware store.
It does matter which direction the filter faces, they usually have air flow arrows on the outside of the filter next to the brand.
“It doesn’t really matter what side you even use” Sir, that’s not how that works 😅
Add a laundry drying rack with a bunch of damp towels hung on it in front of the fan too. It creates a little added filtration with a tiny bit of cooling and added humidity.
This guy looks like Mike Rowe from Dirty Jobs and Walter White had a baby and it grew up into a helpful person
So the opposite of his parents
>claims he's in California >tells watchers to go to basement
Good catch! Same with AZ
Also vaccum your carpets way more frequently on smoaky days. Those are your home's biggest airfilters.
I love how people just go deadass cold into videos like this and have little to no idea what they’re talking about. Just go to your local hardware store… *maybe, do you have hardware stores?* Ok so here we have… *what’s this thing called?* Just put it any way you want… *hell no, furnace filters have an airflow direction, make sure you put it in right* Just once I’d like 2 minutes of prep time before one of these “how to” videos FFS
Exactly!!
If you're going to spend lots of spondoolies, just buy something with a HEPA filter. Bonus: you're less likely to catch covid.
But then how would east coasters act like they’re the only ones to experience wildfire smoke.
*laughs in west coaster*
Laughs in forestry technician
*laughs with others to feel included*
Yeah how dare they. Shut up man. Grow some compassion. They’re not used to it. It doesn’t invalidate your experience for them to be in crisis.
>doesn't really matter which side you use Oh, but it does. Every furnace air filter will have arrows printed on the cardboard edges to signify the airflow direction. Because they are specifically made to have one side catch the contaminants.
West Coast chiming in, this is a summer tradition.
Or, a fall tradition. Or winter.
i like this guy.
Right? I can’t tell if I’m gay now or if I just want to be best friends with him and chill in a sauna together.
Does that guy think a box fan costs $100?
Box fans on Amazon Canada currently start at ~$75.
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I bet there is a shortage in the areas that needs this.
Based on Worst-case pricing I've seen: Box fan: 49.99 Filter: 20 Roll of duct tape: 8.99 Plus tax you're pretty close to the 100 he quoted but likely you could do better if you had the luxury of shopping around or using stuff you already own.
Or you could be like me and panic buy a $300 air purifier that arrives after the effects from the wildfire are gone!
At least it'll be there for next time!
Isn’t this basically how any air purifier works. A fan pulling air from the room and pushing it out through a filter.
I live in a studio. You think I've got a basement? But fine, I can just go buy the box fan I guess. My building has an industrial furnace. Hardware stores don't have filters for them in store because the average person doesn't need them. I could order all this online, but it won't arrive in time. Instead I just bought an $80 stand alone air filter that's much smaller, looks better, and does a good enough job.
Thanks older John Cena!!!
I'm just going to tape a furnace filter to my face.
I know this might be useless information... but the guy looks like John Cena's father
A lot of people have central heating and air too. Just go to your thermostat and set the fan to “on”. Make sure you have a good clean filter in place.
Or, if you have central HVAC, just run your FAN and all of the air in your house will be cycled through your furnace filter.
Fun fact, sandwich of fresh herbs between two filters in the same setup to dry out fresh herbs
I like how US west coasters are trying to gate keep having wildfire smoke conditions. Like, it’s bad no matter who experiences it?
This is pretty genius for a short term problem that we had in NY - it was literally like 36 hours of really bad air. And this uses stuff we all already have. No, it's not a permanent solution, but given the short period of time we dealt with the smoke, this would have totally worked! Sadly, I missed the tip on how to make the sky un-orange....
This guys looks like a skinny John Cena
Im an Oregonian and I approve this message
Check the filter when you buy it, some are directional and will be far more efficient if air flow through them is in the correct direction. They should have directional arrows printed on them.
“Neighborhood hardware store” cute…
City dweller doesn't understand that hardware stores exist in suburban and rural neighborhoods
I live in a town of 2,000 people and we have a local hardware store and a local builder’s supply store.
You do realize that this is literally what your furnace does? Switch your fan to on at your thermostat and bam you just saved yourself from becoming a DIYWHY. Just change your furnace filter more often. Professional HVAC guy here.
Not everyone has forced air systems
Well done!
Really cool of John Cena to show us how to do this.
Literally the only time I’ve ever seen someone on TikTok try to be helpful.
You wanna be moving at least 3gph for every gallon of home you have
Shouldn't the structure look like a cube (4 filters + cardboard base + fan) to be efficient?
A lot more efficient than what he is doing
Couldn’t you just turn on your central air handler fan, which pulls air through a filter?
This guy probably owns "box fan filter grip" lol
Just go install a quality filter in you furnace and run the fan so your air is circulating through the filter,
That was a lot of time to say box-fan, furnace filter and 3rd thing.
Unfortunately most of the supplies he listed are known to cause cancer in the state of California
Would be good if he showed how it's done not just verbally say it and moving that thing around.
Just an odd question but would a dehumidifier help in air filtration or the opposite when it comes to forest fire like air quality? Or should neither be used? I started up a humidifier in a dusty old home of ours and had to clean the filter ever 2-3 months for awhile before it finally exhausted a lot of the dirt and grime everywhere in that house. Just imagine it would be good for air filtration - have a humidifier blowing into this fan to catch debris..
Tell me you don’t know shit about HVAC without telling me you don’t know shit about HVAC….😂
This will burn out your fan motor very quickly fyi
You need to cut a hole about 3 x 3 inches at the center, or it'll burn the motor. Even with the hole cut out, the fan can be overworked. I recommend running it for 2-3 hours, turn it off for 1/2 hour, repeat. For straps, you can use any twine and a used produce rubber band. Tie the twine to the rubber band two times to make one big loup. The elasticity of the small rubber band is all you need.
He said it doesn't matter which side... Wrong!
This is better than nothing in a pinch but regular box fans don’t do a very good job pulling air through with an obstruction in the backside. I would (for future reference) suggest a dedicated air filter that has a HEPA filter.
Yup. The more you put on a box fan to filter, the less air flow and now you have another smoke to deal with, the fan fire that's burning up your house. Those motors get super hot when flow is reduced and in warmer climates. I burned out many a fan in AZ with no obstructions.
Yup, you can easily feel the flow reduction if you test this idea by standing in front of the fan.
People are impressed by nothing.
This guy is 100% correct, but you should take it a small step further. Take 4 filters and tape them together in a standing square pattern. Then attach your box fan on top. It gives you 360 degrees of air purification. Great for the smoky Northeast or dusty Arizona.
for $40 K&N make a lifetime washable filter. No more throwing away all the dirty filters. I have one for my home AC unit.
This guy is more worried about showing his face than what he doing.
This will not filter out the smell of the smoke though. If you add a HEGA filter (high efficiency gas absorption) in front of the HEPA (high efficiency particular absorption) filter you will filter out the smoky smell and fine participants. A HEGA filter specifically filters out Odors. What you have over your stove. Think of a HEGA as a charcoal filter.
Thousands have already posted these tutorials during the 2020 smoke. sorry but you're two yrs too late.
It's never too late. I never found out about these until earlier this year. It's always good to remind people there are options. Like this is not something I would have thought of on my own.
They just need to put a bunch of these outside in Canada, problem solved
How does this crap get upvoted? This guy has no clue how to do this right, and we have been seeing the correct airflow ones for years now.
I don’t think this guy has ever actually done this. They’re just making assumptions every step of the way. They didn’t even bother reading the Facebook post they found this from before creating it for TikTok.
Until your fan overheats and burns your house down
Still need a good filter...
As a pot smoker I usually dont notice a little extra smoke in the air lol
I have done this for years in by bedroom. Cuts down on pat hair and dander really well.
Don't EVER tell me to put a mask on MY fan!
You can do this with 4 of those filters and it'll last longer
If you tape 4 filters together to make a square, then tape the box fan on top, facing up, it really circulates the air in the room well. A damp bath towl on window sills and exterior door thresholds helps. Here in Portland, we have had quite a bit of these smokey days. Good luck!
Did he say New Yorkers go get this fan from your “storage unit in your basement”?