[cosmolev]

I have smartairfilter's Cannon purifier. As all those standalone purifiers it works only with windows completely closed.

I went for ventilation systems that take air from outside, filter it and then bring it inside the room. Namely Xiaomi MJXFJ-300-G1: https://www.xiaomitoday.com/xiaomi-mijia-air-purifier-mjxfj-... I've installed one in every bedroom.

[driverdan]

That seems quite expensive for what it is. For that price I'd expect it to have an efficient heat exchanger.