DIY filtration - Corsi-Rosenthal boxes - fancy update

[wathe]

(Dec 31/22 ETA: fancy update in new post.)

 

We made one.

More about them here.

Box fan from big-box store $30

High filtration furnace filters (MERV 13 equivalent) $40

Some packing tape

Cardboard from the fan box, and one extra piece 17x17 inch for the bottom

We used 16x25 inch furnace filters instead of the recommended 20x20 inch because:  1) I can re-use them in the furnace when we are done with the thing (if I can get the tape off) and I can get a four pack at Costco for less than half the price of four 20 inch filters purchased individually elsewhere.  I adapted by putting a cardboard shroud on both sides of the fan to block leaks.

The cardboard shrouds on the fan are to prevent backdraft through the corners (which we tested with a piece of thread - yes, there is a back draft, and the shroud eliminates it)

The popsicle stick is hiding our family name, which puns will with covid - my kids have a strange sense of humour.

Edited December 31, 2022 by wathe

[Catwoman]

Very cool!!! Thanks for the link to the instructions!

[J-rap]

Neat!  I'd never heard of these until Thanksgiving, when my BIL had built one for the occasion.  It seems so simple, yet I hear they're very effective.

[crazyforlatin]

I’m going to have Dd and Dh work on this during the break!

[saraha]

Someone had suggested this a few months ago when I asked about recommendations for a filter for ds21’s apartment. Smoke filters into his apartment from the apartment below him and it made everything stink. He decided he didn’t have room for the whole 4 sided box in his little apartment so set up the box fan with one filter on the back of it and it works like a charm! No smoke smell at all even though you can smell it outside his door on the stairwell, and it cost him $25 dollars total with $10 every so often for a new m13 filter

[MEmama]

Can I ask, why not just use a HEPA air purifier? 

[KSera]

2 hours ago, MEmama said:

Can I ask, why not just use a HEPA air purifier? 

It costs nearly $1000 to get an air purifier that can move as much air and filter as efficiently as this DIY version can do for $80-120 (depending where you live). There are a lot of even expensive Hepa purifiers being sold that do indeed remove virus from the air, but they do it so slowly that it’s almost useless (in an occupied room, it’s useless if the device isn’t even removing it as fast as new virus is being added to the air by an infected person breathing). That’s not to say there aren’t good options for people if they want to buy an off the shelf version. Somewhere is a good chart I will try to find. 
 

eta chart from 

 

Edited December 19, 2021 by KSera
Added chart

[Halftime Hope]

13 hours ago, wathe said:

We made one.

More about them here.

Box fan from big-box store $30

High filtration furnace filters (MERV 13 equivalent) $40

Some packing tape

Cardboard from the fan box, and one extra piece 17x17 inch for the bottom

We used 16x25 inch furnace filters instead of the recommended 20x20 inch because:  1) I can re-use them in the furnace when we are done with the thing (if I can get the tape off) and I can get a four pack at Costco for less than half the price of four 20 inch filters purchased individually elsewhere.  I adapted by putting a cardboard shroud on both sides of the fan to block leaks.

The cardboard shrouds on the fan are to prevent backdraft through the corners (which we tested with a piece of thread - yes, there is a back draft, and the shroud eliminates it)

The popsicle stick is hiding our family name, which puns will with covid - my kids have a strange sense of humour.

This is awesome.  @wathe could you post the underside view?  I'd like to see how you seal the back side of the fan to the filters. Thanks! 

[wathe]

1 hour ago, Halftime Hope said:

This is awesome.  @wathe could you post the underside view?  I'd like to see how you seal the back side of the fan to the filters. Thanks! 

Backside of the fan has a cardboard shroud just like the top.  Seal the edges shroud to fan with tape, seal the edges filter box to shroud with tape. 

[wathe]

5 hours ago, MEmama said:

Can I ask, why not just use a HEPA air purifier? 

What @KSera said:  value for money.  The graph she posted was for a single filter version.  The four filter version that we built apparently rivals the very best home HEPA units, at a small fraction of the cost.  Components were very easy to source.

We'll also be able to re-use the components.  The filters are the same size that my furnace takes, so can re-use if there is life left in them.  The box fan can be just a box fan.

And it's a homeschool science lesson that really engaged my kids - priceless!!

One silver linings of this pandemic (if such a terrible thing can be said to have silver linings) for me has been the endless opportunities to schoolify it in a very authentic/engaging way - physiology, virology, epidemiology, immunology, statistics, exponential vs linear growth, how to read a graph, public heatlh policy, social justice, international affairs, politics, psychology, critical appraisal of news and scientific publications, critical appraisal of media and social media, and now physics and aerosol science

 

[ktgrok]

Maybe a dumb question - but how does using this compare to running Central AC, with fan turned to "on", with a Merv 13 filter?

Like, how much air is moved/cleaned with one of these versus a typical AC with Fan on all the time, I wonder?

[wathe]

45 minutes ago, ktgrok said:

Maybe a dumb question - but how does using this compare to running Central AC, with fan turned to "on", with a Merv 13 filter?

Like, how much air is moved/cleaned with one of these versus a typical AC with Fan on all the time, I wonder?

I don't know.

My completely subjective opinion: The CR box moves A LOT of air.  Subjectively way, way more than my furnace fan.

[Halftime Hope]

4 hours ago, wathe said:

Backside of the fan has a cardboard shroud just like the top.  Seal the edges shroud to fan with tape, seal the edges filter box to shroud with tape. 

Thanks! that makes sense, and I should have thought of it.  :-) 

[Clarita]

This is what we used last fire season. It doesn't look fancy but it works, better than any expensive filter. It comes out of the physics; this video has a great explanation. We do put the hefty filter on our central air unit, but when it gets bad this configuration is what we have to use.

 

[wathe]

Frivolous update:  Not only does it clean the air, it provides engaging Christmas entertainment for all ages:

This thing levitates balloons like nobody's business.  The same balloon has been suspended in space for 2 hours now.  No strings attached 🙂  

Also fun to attach streamers.  Levitate ping pong balls.  Creative use of ping pong balls and toilet roll tubes, and bits of cardboard, and balloons with various coins stuffed in them to add weight....

And all the whack-the-other-guys-balloon-while-defending-your-own sort of nonsense you can imagine......

[wathe]

I anticipate that wrapping paper and ribbons will only add to the fun tomorrow.

[Clarita]

3 hours ago, wathe said:

Also fun to attach streamers.  Levitate ping pong balls.  Creative use of ping pong balls and toilet roll tubes, and bits of cardboard, and balloons with various coins stuffed in them to add weight....

I need to do this if we have to utilize ours again!

[Debbirie]

On 12/25/2021 at 5:02 AM, wathe said:

Frivolous update:  Not only does it clean the air, it provides engaging Christmas entertainment for all ages:

This thing levitates balloons like nobody's business.  The same balloon has been suspended in space for 2 hours now.  No strings attached 🙂  

Also fun to attach streamers.  Levitate ping pong balls.  Creative use of these ping pong balls and toilet roll tubes, and bits of cardboard, and balloons with various coins stuffed in them to add weight....

And all the whack-the-other-guys-balloon-while-defending-your-own sort of nonsense you can imagine......

Sounds very interesting! I don't have much of an imagination and I would never have thought of that 😄

Edited October 28, 2022 by Debbirie

[Bambam]

We attached some ribbons to our HEPA filter - the cat loved it. 

[wathe]

Since this thread has been resuscitated, I might as well update:  The CR box is still going strong.  We use it whenever we have anyone in the house who doesn't live with us, and when any of us is feeling under the weather. We also cart it along to my parents when we visit.  

It still floats balloons beautifully.

Worth every cent of the approx $80 we spent on it.

[wathe]

 

Fancied up the CR box for the holidays!.  I put a string of LED lights inside it.  The blur above  the fan is a streamer dancing in the clean exhaust air.