Corsi–Rosenthal Box | Hacker News Reader

Corsi–Rosenthal Box

en.wikipedia.org

81 pointslelf21 comments

I built one of these back during the january omicron wave (us). Mostly out of 'why not' boredom because I already had a box fan, a roll of duct tape, and a near infinite supply of cardboard from amazon, just had to buy four filters from home depot.

Six months later I have to replace the filters because they are a thick dusty grey. Went from looking like white paper with blue flecks in it to looking like grey jersey/t-shirt fabric. If even a tenth of what it caught was otherwise destined for my lungs then this was a big win.

People have been building these things for years in the Bay Area now with 1 filter (strapped to the back) or 2 (making a triangular prism), to deal with the smoke from the fires. Surprised that isn't mentioned in the article. I first learned about them in 2017 but I'm sure people were doing it prior.

Here’s an article from one of the namesakes (the origin story is somewhere on the site): https://www.texairfilters.com/testing-the-efficiency-of-merv...

Does anyone know why box fans are so hard to get hold of in Europe? In Germany they seem very rare and expensive.

Do these things make a noticeable difference? I have never been in a heavily polluted atmosphere, then scrubbed by an air purifier.

I’ve always assumed consumer air purifier units are a marketing fad. Your air is not only accelerated but also cleaner. Is that not right?

Clearly very different for large-scale / industrial uses etc.

The Corsi-Rosenthal design is legit--it uses paper filters which are quiet effective at removing pollutants from the air in a few air changes.

It's the filter-less / ion / electrostatic air cleaners that have quite questionable or non-existent air filtering qualities.

It’s visible on the filters that they remove particles (they turn from white to gray). The one I have has also a sensor for particulate matter that goes down to 0 or 1 if you let it run. I can also see that it’s really measuring things because you see the effect of making the bed (goes up a bit), opening the windows (goes down when there is bad air) or frying food (goes up to levels in China or India).

Air pollution also is one the leading causes of death and disease burden: https://ourworldindata.org/air-pollution

Did you add the sensor in a DIY setup?

this is actually a major disruptor if you look at prices of air purifiers... sure it's no IQAir where it outputs absolutely pristine air, but due to it's throughput when recycling air in an indoor setting this absolutely thrashes everything on the market

So they got named in 2020? I've been building these for years. Edit: Also, they're not as practical as one might think, because they take up a lot of space. I run mine in my basement, but we use single smaller Fellowes and Rabbit Air filters upstairs.

UV light fixtures "Upper room UVGI (Ultraviolet germicidal irradiation)" also seems to be a promising air-cleaning technique, with possibly fewer moving parts and less power draw than this.

https://twitter.com/RealSexyCyborg/status/152709990924505088...

UV light can sanitize (kill germs) but it won't clean (remove particles).

UV doesn't really remove pollutants but chemically alters them which can also have unintended bad effects:

https://pubs.acs.org/doi/10.1021/acs.est.1c02582

i think this is trying to raise awareness of those that produces ozone which is definitely a bad idea..

"careful selection of the UV wavelength and light intensity used in these devices may be able to mitigate unintended chemistry."

Far UV-C 222nm done correctly would be great!

I've been using a box fan with a furnace filter strapped to the back for years to deal with cat litter dust. My vet recommended using air cleaners to help an asthmatic cat, this setup made a significant and immediate improvement.

My fan is quite loud, so I've got a motion sensor to only turn it on after the cat has used the box.

Never heard of Corsi or Rosenthal from the Bay Area, but I’ve seen many similar DIY air cleaners on YouTube over the years.

Here’s a recent example of Matthias Wandel testing different air cleaners including his home made one:

https://youtu.be/rDZ9yUdM2wA

Could someone explain why air is "pulled" through the filters (blown out of the box) instead of "pushed" (blown into the box)?

Does it increase airflow, or filtering, or what?

Depending on your environment, this will make the fan last longer by preventing dust from getting to the motor.

I think the filters used are designed to filter high volumes of air moving at a relatively low speed - think about how they fit in a home central air system, they’re at the very end of the system before the fan and they have an entire house of ductwork between the blower and them.

Having built one, I don’t see any way the filter stands up to a box fan at high from 12” away. The filters are just media reinforced by cardboard.

A furnace fan will move a lot more air than a box fan would.

The reinforcement on the filters really depends on how much filtering they do. For example, this filter[0] has metal to help keep the filter media in place, but this one[1] has nothing.

The key difference is the MERV rating, the first one is a 13, the second is a 2. The higher the rating the more it filters, but the higher rating also makes it more difficult for the fan to pull air through and require better reinforcements to prevent the filter from getting sucked into the fan.

[0] https://www.homedepot.ca/product/filtrete-filters-healthy-li...

[1] https://www.homedepot.ca/product/hdx-20x20x1-fiberglass-air-...

Keeps the fan clean and extends its life.

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