[geeks] DIY project, maybe? (Cheapo bedroom air purifier)

[Patrick Giagnocavo]

So both neighbors, on both sides of the townhouse we are in, are heavy
smokers.  This causes a problem at night time regardless of it being
winter or summer.  I tried positive pressure, it helped somewhat but
without going around and doing a lot of sealing, it is not enough.

Checking out the prices of air filters, then checking the cost of the
replacement filters, leads me to believe that is an enormous fraud
perpetrated on consumers.  Given that, broadly, the filter media has a
fixed cost per square foot (for the same filter media in different size
filters), I figure that the markup on this stuff is about 10-20 times or
more from what the same quality and type of 3M HEPA furnace filter goes for.

There are no air purifiers that do what is needed, without replaceable
filters.

So my thinking is this:  build a wooden box containing some big but
quiet fans, and then build it so that I can use a common sized furnace
filter.  Add a pre-filter (simple plastic mesh) and space to hold an
activated carbon filter in front of the HEPA filter, and I should have
something that over the long run will be much cheaper.

Anyone ever done something like this?  My concern is the fans, actually,
they need to be sized properly .

--Patrick