5 ms·

In my office I have a Costco MERV 13 furnace filter tied to a box fan. I am down to 0 PM2.5 after a couple of hours. In my case it's just a 20" box fan with a

by bb88 3y ago

In my office I have a Costco MERV 13 furnace filter tied to a box fan. I am down to 0 PM2.5 after a couple of hours. In my case it's just a 20" box fan with a 20" square filter bungee corded together. The filters last 3-4 months, but are commodities at this point.

29athrowaway 3y ago
That's a clever trick. Creating the air pressure with a box fan and then filtering using a MERV filter. I guess if you can find a 20x20 box fan and attach a 20x20x1 filter to it you can do this easily. But how much the filters last depend on a variety of factors. If you have pets (with fur) your filters will last much less.
- bb88 3y ago
  What's interesting is that if you look on amazon, MERV 13 filters + Bungee Cords + 20" box fans are commonly ordered together. Further you can do a 20x20x4" MERV 13 to increase the lifespan of the filters. It also beats the price of buying specialized HEPA filters for a particular brand of air filter.
- lamontcg 3y ago
  Make a cube out of 4 MERV 13 filters and a box fan on top and the cardboard the box fan came in on the bottom and secure it with duct tape. That'll help reduce the load on the box fan and push more air through more filters.
- bredren 3y ago
  It is called a Cosri-Rosenthal box [1]. I've built three variations on these using different kinds and sizes of Filtrete filters they are very cheap and effective. The downsides are that they take up a lot of space, are a big eye sore and awkward to carry and move. They also can make a lot of (white) noise on high, which can mask sounds you want to hear. They're great for special situations like wildfires or out of the way areas like basements where looks don't matter. For common living spaces we use Coway Airmega AP1512's which are relatively compact, auto cycle up and down fan speed and are much more attractive than DIY stuff. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box
  - 29athrowaway 3y ago
    And replacing the filter is problematic.
hollerith 3y ago
There is a report of a fire started by overheating of the box fan motor in such an ad-hoc purifier. The box fan is not designed for this application. Humbly suggest not running this unattended.
- btbuildem 3y ago
  A properly built CR box (bottom base, four filter walls, fan on top) relieves this concern. Ample airflow around the fan and four filters let enough air through.
- hollerith 3y ago
  (Replying to myself.) Here is the report I refer to: https://news.ycombinator.com/item?id=21382994 https://news.ycombinator.com/item?id=21382994
- bredren 3y ago
  This concern comes up often against DIY filtration systems like this but I've yet to see a study showing this to be the case. I have seen this study [1] that says no fire hazard is created by motor stress from these kinds of setups. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

by bb88 3y ago

29athrowaway 3y ago

That's a clever trick. Creating the air pressure with a box fan and then filtering using a MERV filter. I guess if you can find a 20x20 box fan and attach a 20x20x1 filter to it you can do this easily. But how much the filters last depend on a variety of factors. If you have pets (with fur) your filters will last much less.

bb88 3y ago
What's interesting is that if you look on amazon, MERV 13 filters + Bungee Cords + 20" box fans are commonly ordered together. Further you can do a 20x20x4" MERV 13 to increase the lifespan of the filters. It also beats the price of buying specialized HEPA filters for a particular brand of air filter.
lamontcg 3y ago
Make a cube out of 4 MERV 13 filters and a box fan on top and the cardboard the box fan came in on the bottom and secure it with duct tape. That'll help reduce the load on the box fan and push more air through more filters.
bredren 3y ago
It is called a Cosri-Rosenthal box [1]. I've built three variations on these using different kinds and sizes of Filtrete filters they are very cheap and effective. The downsides are that they take up a lot of space, are a big eye sore and awkward to carry and move. They also can make a lot of (white) noise on high, which can mask sounds you want to hear. They're great for special situations like wildfires or out of the way areas like basements where looks don't matter. For common living spaces we use Coway Airmega AP1512's which are relatively compact, auto cycle up and down fan speed and are much more attractive than DIY stuff. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box
- 29athrowaway 3y ago
  And replacing the filter is problematic.

hollerith 3y ago

There is a report of a fire started by overheating of the box fan motor in such an ad-hoc purifier. The box fan is not designed for this application. Humbly suggest not running this unattended.

btbuildem 3y ago
A properly built CR box (bottom base, four filter walls, fan on top) relieves this concern. Ample airflow around the fan and four filters let enough air through.
hollerith 3y ago
(Replying to myself.) Here is the report I refer to: https://news.ycombinator.com/item?id=21382994 https://news.ycombinator.com/item?id=21382994
bredren 3y ago
This concern comes up often against DIY filtration systems like this but I've yet to see a study showing this to be the case. I have seen this study [1] that says no fire hazard is created by motor stress from these kinds of setups. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box