[clarry]

Speaking of air purifiers, does anyone have recommendations for one that is quiet and still effective?

I have a pair of Electrolux EAP300s, in small rooms.

Unfortunately on the lowest manual setting ("Quiet") they hardly do anything for air quality. And they're still louder than I like. I think they really optimized for cost; these devices feel very light and plasticy, the fan sounds cheap and has an uneven tone to it, and its speed keeps oscillating back and forth. The purifier itself is also not stable and it can make an annoying noise if placed on a surface that ends up vibrating along.

I also thought about DIYing one with noctua fans (which I know are quiet, and I have plenty of them in my PCs), but I suspect they're not going to be very effective.

[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.

[frank2]

One thing to keep in mind is that an air purifier with a squirrel-cage fan (the kind of fan needed to pull enough air through a HEPA filter) makes a very pleasant sound that is good for masking, e.g., banging noises from neighboring apartments. I regularly run mine just to mask noise. So being loud can be considered a feature.

[emrehan]

Exposure to noise degrades hearing and have psychological consequences.

[aidenn0]

Levoit makes ones that are a lot quieter than the ones you see for around $100, but you will pay a lot more for them. I still wouldn't call them "Quiet" though.