[mdp2021]

> virtually silent

Decibels?

I have seen air purifiers publicized as exemplary silent, and people unable to bear the noise of the minimum fan speed.

There may also be a matter of the exact sound - maybe some are less disturbed by (say) a hum instead of a hiss; it probably has to be tried.

[rsynnott]

While I don't have mechanical heat recovery ventilation, I've been in lots of apartments and houses that do (it's virtually mandatory for new builds here). You won't know it's there unless you're in the room that the device lives in, and even then it's not loud.