I don't know if I'd mentioned this here, but I have Guinea pigs... Long story short, Pigs eat hay and I have developed a very bad hay allergy.
To help alleviate this, I bought 2 20" box fans, 2 very good filtrete furnace/AC filters, and some masking tape. I found the plans (if you can call "tape filter to fan" plans) on google.
Honestly, I was skeptical, but they seem to be working. I run them on slow, and a lot of air gets blown back, but I'm going for a cumulative effect and am really just trying to clear all the air. Also, it keeps noise down.