Simple suction air filter: items and preventing implosion

[r19]

I want to make a simple air filter(for dust and air pollution) but was a bit confused about some stuff. Basically I've decided to use an exhaust fan to create a vacuum in a sealed box and the air to come in through the filters. Box fans aren't available here, so that can't be used. I want to create a 'CADR' of 250(CFM is not accurate benchmark of purifier performance, since air might repeat through the system). Such filters are available here for 150$, so though this will not save much money(time) for me it could be helpful for other people here. Total cost would be 40$.

>I'm thinking of going with a 40db 8in 1400rpm fan, 450CFM. I've used this to get an idea of relationship between CFM and CADR - http://www.theairpurifiers.com/air-purifier-performance.html . A 6in 250CFM fan might be fine but not sure
>Do I really need HEPA / Carbon filters? They cost 15$ here, and since simple cloth might filter 50%, but isn't it the same if the air moves twice through it, and air will move faster though it anyway. Or does the 99.5% figure mean it filters 99.5% types of particles - don't think so
>One thing I'm afraid of is an implosion if pressure gets too low in the box, it could be a hazard. I'm thinking of making a hole and covering it with a plastic film so it pops before
>Does anyone know of some harmless coating or something that could make wood not air porous, so that I could use wood <1in? I was first thinking of using cardboard instead of wood first and maybe taping it, but that could catch fire

Keep in mind that I don't have that much knowledge or DIY experience. Just posted here since I though people here would have a good idea.

Thanks

 

[anorlunda]

You haven't said anything about your filtering requirements. Do you want to filter out the smell of smoke? Biohazards? Insects?

 

[r19]

You haven't said anything about your filtering requirements. Do you want to filter out the smell of smoke? Biohazards? Insects?

I want to filter out dust, PM 2.5 and PM 10 pollutions. Filtering odors would be nice too, but I think a carbon filter would be necessary for that and that costs another 15$ here.