3 ms·

I tried that, the box fan had pretty anemic airflow through the filter. I'm sure it was doing something, especially if it was blowing directly at me, it didn't

I tried that, the box fan had pretty anemic airflow through the filter. I'm sure it was doing something, especially if it was blowing directly at me, it didn't seem like it was really cleaning the whole room. Then I got a $200 air purifier with a HEPA filter and it has much better airflow, thus more air exchanges per hour. I think fan blades aren't that efficient at pushing against the high flow resistance of a HEPA filter, while the squirrel cage blower in a dedicated air purifier is.

pacman2 5y ago
Doubt it. A self build filter basically outperforms all bought systems in tests. The answer is easy: A self build system blows the air through a filter. Nearly all commercial systems suck the air trough a filter. Big difference.
- Johnny555 5y ago
  What’s the difference between blowing or sucking air through a filter?
  - strogonoff 5y ago
    The Particle Counting folks[0] blew it through, and they seem to have done their research. I’m sure they wrote about it in their blog somewhere. [0] https://particlecounting.tumblr.com https://particlecounting.tumblr.com
    - Johnny555 5y ago
      Hmm...that doesn't really answer the question and since so many high ranking purifiers (plus many industrial HEPA filters) use the same "squirrel cage fan to suck air through the filter" design, I don't believe it's true that there's a big advantage to blowing versus sucking. I can believe that some home built box fan purifiers out perform some commercial units, but not as a blanket statement that a home made filter outperforms all commercial units.
      - strogonoff 5y ago
        I’m not saying I necessarily agree with this: > A self build system blows the air through a filter. Nearly all commercial systems suck the air trough a filter. Big difference. But if you’re strapping a filter to a fan, it’s probably more efficient to blow through, since the air will be more focused (plus, it’s easier to mount due to front being flatter). > I can believe that some home built box fan purifiers out perform some commercial units, but not as a blanket statement that a home made filter outperforms all commercial units. Agreed. I recall seeing the stats they published and it looks like there are good purifiers among the more expensive ones (US$1000+), but apparently even in that price class they’re hit or miss and don’t always perform as well as a DIY solution could. Generally there’s a lot of information asymmetry, manufacturers want their margins so commercial air purifiers might often use something custom rather than a standard-compliant HEPA filter (either worse or slightly better but 10x more expensive than it should be) and make it difficult or impossible to swap it for something from a trusted third party. They’re counting on very small percentage of customers having properly calibrated particle counting equipment set up at home, they get away with providing misleading tech specs like CADR (or not providing them at all), and so on.
- jimbob21 5y ago
  Can you give a link to the best setup?
jjeaff 5y ago
if you are getting slow airflow, then you can increase the surface area of the filter medium by either buying a thicker, pleated filter or, you can duct tape multiple filters together in a cube shape with the fan being one side of the cube. That will give much more surface area for the fan to pull through.

pacman2 5y ago

Doubt it. A self build filter basically outperforms all bought systems in tests. The answer is easy: A self build system blows the air through a filter. Nearly all commercial systems suck the air trough a filter. Big difference.

Johnny555 5y ago
What’s the difference between blowing or sucking air through a filter?
- strogonoff 5y ago
  The Particle Counting folks[0] blew it through, and they seem to have done their research. I’m sure they wrote about it in their blog somewhere. [0] https://particlecounting.tumblr.com https://particlecounting.tumblr.com
  - Johnny555 5y ago
    Hmm...that doesn't really answer the question and since so many high ranking purifiers (plus many industrial HEPA filters) use the same "squirrel cage fan to suck air through the filter" design, I don't believe it's true that there's a big advantage to blowing versus sucking. I can believe that some home built box fan purifiers out perform some commercial units, but not as a blanket statement that a home made filter outperforms all commercial units.
    - strogonoff 5y ago
      I’m not saying I necessarily agree with this: > A self build system blows the air through a filter. Nearly all commercial systems suck the air trough a filter. Big difference. But if you’re strapping a filter to a fan, it’s probably more efficient to blow through, since the air will be more focused (plus, it’s easier to mount due to front being flatter). > I can believe that some home built box fan purifiers out perform some commercial units, but not as a blanket statement that a home made filter outperforms all commercial units. Agreed. I recall seeing the stats they published and it looks like there are good purifiers among the more expensive ones (US$1000+), but apparently even in that price class they’re hit or miss and don’t always perform as well as a DIY solution could. Generally there’s a lot of information asymmetry, manufacturers want their margins so commercial air purifiers might often use something custom rather than a standard-compliant HEPA filter (either worse or slightly better but 10x more expensive than it should be) and make it difficult or impossible to swap it for something from a trusted third party. They’re counting on very small percentage of customers having properly calibrated particle counting equipment set up at home, they get away with providing misleading tech specs like CADR (or not providing them at all), and so on.
jimbob21 5y ago
Can you give a link to the best setup?

jjeaff 5y ago

if you are getting slow airflow, then you can increase the surface area of the filter medium by either buying a thicker, pleated filter or, you can duct tape multiple filters together in a cube shape with the fan being one side of the cube. That will give much more surface area for the fan to pull through.