Air Purifiers

No central air or heat, so in winter windows are cracked and in summer windows are screened but opened. I bought the air purifier to help with allergies and after 2 nights it does seem to help, but think I need to go back and get the larger one. This one is for room 10 x 12 and my room is 16 x 13 and is connected to kitchen with no dividing door. Am I fighting a losing battle, or will this unit help pretty bad allergies (I think mostly to dust)? Would love to hear your experiences.
P.S. I bought the Holmes brand with Hepa type filter.
Thank you.

Just wondered if they work. They are too expensive just to get one and "see" if it works like they say it does. Anyone have any bad experiences?

Thanks!!
How is it on dust? Do you find yourself dusting as often? Seems like my whole house is made of dust.
Lilli D - I could not get the link to work.

brands looking at: bionaire, homes, honeywell. any experiences? willing to pay around 0.