I am an asthma sufferer who is allergic to pollen (big time) and
possibly to dust. I am trying to convert my (small) bedroom into an
"oasis" of clean air to sleep in. So far I've installed a fancy HEPA
filter that recirculates air, I made the windows and the doors air-
tight, and I moved all furniture/stuff out except for the bed. I
checked the air with a laser particle counter, and after 15 min of the
HEPA working at the highest speed the amount of ~1 micron particles in
the air goes down by a facor of 10 compared to the outside air. Great.

The problem is that I don't have any ventilation in the room. And I am
paranoid to leave the windows open. So I am thinking that perhaps the
HEPA recirculating filter I bought was a mistake, and perhaps I
should've installed some sort of a filter that takes the air from the
outside, filters teh air, and blows the air in. What would be the most
affordable way of doing that (under 1k?)? The room is about 12x16
feet, standard height. Wouldn't an outdoor HEPA require replacement
more often than an indoor HEPA? Besides, I rent my house, so, I can't
build/break walls and all that. Minimum impact preferred.