[qpiox]

It depends on what noise level is acceptable for you and the room size.

Out of 30 or so air purifiers available in shops here, of all the ones that are in the $100-500 category, the Winix P/U450 are able to push the largest amount of air under the constraint of <40db.

HEPA filters are rated at which air speed they are most effective and how much pressure is needed. The ammount of pressure will only rise as the filter is saturated with dirt. You need a sufficiently powerful fan, and fans that are both powerful enough and quiet enough are very expensive.

[leetbulb]

I have two Winix HR1000. They have extremely powerful blowers and are quiet when not in "turbo" mode. The turbo mode is actually pretty good for white noise when sleeping. I've been running them 24/7 for years now and they are still working great.

[clarry]

I think EAP300 is rated 26dbA on its lowest level.

I don't mind expensive, I'm tired of buying poor quality products.