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A small DIY air purifier

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Re: A small DIY air purifier

#121

Post by storyinmemo »

majos wrote: post #94

May as well ask here: do air purifiers have meaningful health benefits for generally healthy people? I get that you change the filter and it's filled with grey muck and that's gross, and that the filters change particulate content in air, but is there good evidence that doing those things improves health if you don't already have some sensitivity to air pollution or live in a highly polluted area? I don't know if "Lu…

PM 2.5 seems to be like radiation: the more you get, the more you're likely to be affected, even at lowish levels.

https://qz.com/1166010/air-pollution-even-at-levels-that-mee...

Re: A small DIY air purifier

#122

Post by spookthesunset »

In addition to the old "strap an HVAC sized air filter on the front of a box fan" tip, I'd add that it is important to maintain a positive air pressure in your living space. The only path air should enter your dwelling from the outside is via your air filter.

You can do this by putting the box fan in a window and sealing up any gaps with something like cardboard or thick plastic sheeting. On the outdoor end of the fan, put your filter. Close all other windows & doors in the house.

Keeping a positive indoor air pressure this way makes sure all the air in your house is filtered. Obviously you'll want to make sure your box fan's filter is rated for smoke / particulate matter.

Re: A small DIY air purifier

#123

Post by fareesh »

Nexxxeh wrote: post #110
apta wrote: post #84

Earlier quoted context omitted.

Do you strap them to the front or the rear of the fan? Doesn't having them on the front (i.e. where the air blows out) mean that the fan will get dirty since it's sucking the air in?

You may wish to use a cheap thin washable pre-filter either way. It will catch a lot of the hair before it hits the fine filtration, which you can then just wash off the pre-filter, making it easier and cheaper to maintain.

Do you have a link to one of the cheap thin washable pre-filters that I can look at as a reference for what to buy?

Re: A small DIY air purifier

#124

Post by compressedgas »

sfgweilr4f wrote: post #80
loldot_ wrote: post #60

I don't know how effective they are compared to these devices, but I much prefer to keep plants with air purifying qualities. NASA did a study on a variety of air purifying plants in 1989: https://ntrs.nasa.gov/search.jsp?R=19930073077

Hasn't that been partially debunked or at least conditions placed on how effective they are? I lost the article that reviewed it.

Potted plants don't improve indoor air quality: https://news.ycombinator.com/item?id=21464423

Re: A small DIY air purifier

#125

Post by lm28469 »

OJFord wrote: post #88
cosmolev wrote: post #81

Earlier quoted context omitted.

+1. Together with a test in the same environment without a purifier at all. PM count drops down to almost 0 in a room with closed windows with a breathing person inside. Lungs of a person act as a perfect purifier.

> Lungs of a person act as a perfect purifier. Is that good? I mean, of course it's good that PM doesn't just pass straight into our bloodstream, but isn't our lungs doing the purifying exactly the thing that people try to avoid with mechanical air purifiers?

The whole point of filtering air for PMs is to avoid having them in your lungs so I'm pretty sure that's not "good".

Re: A small DIY air purifier

#126

Post by aidenn0 »

clarry wrote: post #24

Speaking of air purifiers, does anyone have recommendations for one that is quiet and still effective? I have a pair of Electrolux EAP300s, in small rooms. Unfortunately on the lowest manual setting ("Quiet") they hardly do anything for air quality. And they're still louder than I like. I think they really optimized for cost; these devices feel very light and plasticy, the fan sounds cheap and has an uneven tone to i…

Levoit makes ones that are a lot quieter than the ones you see for around $100, but you will pay a lot more for them. I still wouldn't call them "Quiet" though.

Re: A small DIY air purifier

#127

Post by amluto »

My general theory is that HEPA makes sense for filtration where a single pass is all you get. So it makes sense for vacuum cleaners, air intakes, and such. But, for room air cleaning, what matters is the rate at which particles are removed, not the cleanness of the air coming out. So, for recirculating, something like a MERV 13 filter seems like a better choice: it lets more particles through on each pass, but it also restricts airflow less.

Re: A small DIY air purifier

#128

Post by jakeogh »

marcinzm wrote: post #50
kn100 wrote: post #6

This is a really cool project but frankly you can do it a lot cheaper. Find the cheapest box fan you can find, and find the cheapest HEPA filter you can, and strap the HEPA filter to the front. To improve air purification even futher, slap an activated carbon filter on the front too, and your air purifier now filters VoCs! For cheap Activated Carbon Filters, look into the kind used for Aquarium filters. They'll work…

This may or may not work, cheap box fans aren't designed to push/pull air through obstructions (ie: low static pressure) and HEPA filters are giant obstructions. So instead of the air going through the filter it'll go through gaps, around the edges of the blades, etc. I used a cheap box fan for some DIY ventilation and the loss in airflow is massive after filter and ducting.

I have a box fan on low 24x7 with a 12 on the input and a 7 on the output. That's not a HEPA rated filter set, but it's fantastic. Allergy season just went away (while in my room) when I started using it a few years ago. I also tried a 3 on the output, and that worked as well, but the flow was noticeably lower. The fan is cheap, $20. I change the filters every few months, and it always looks like I waited too long.

Re: A small DIY air purifier

#129

Post by [deleted] »

clarry wrote: post #24

Speaking of air purifiers, does anyone have recommendations for one that is quiet and still effective? I have a pair of Electrolux EAP300s, in small rooms. Unfortunately on the lowest manual setting ("Quiet") they hardly do anything for air quality. And they're still louder than I like. I think they really optimized for cost; these devices feel very light and plasticy, the fan sounds cheap and has an uneven tone to i…

[deleted]

Re: A small DIY air purifier

#130

Post by GR34T3R4L4RM »

logfromblammo wrote: post #106
post_break wrote: post #67

Earlier quoted context omitted.

If you want this to actually work, you take a box fan, and 2 filters. You make a triangle and then some cardboard on the top and bottom to fill the gap. This increases surface area and reduces the stress on the fan due to pressure drop. Slapping a filter directly on to the box fan is going to kill the fan very quickly. https://i.imgur.com/SX1RloH.jpg

Or ditch the cardboard, and use 5 square HVAC filters to make a true "box fan".

https://imgur.com/gallery/jtECP9C
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