[5e92cb50239222b]

If your outside air is clean enough that you can afford to open a window with a purifier running, you probably don't need the purifier. I have two Xiaomi ones running 24/7, with CADR 300-350 on both. In colder months (which are 7-8 per year) they're running at maximum speed for most of the time (~2300-2400 RPM). Every window and door is shut, all gaps are plugged with expanding foam. Even with all that, the indoor PM2.5 almost never goes below 2-5 µg/m³, with jumps up to 30-40 µg/m³ when it's really bad outside.

Opening a window even for a few millimeters is enough for PM 2.5 to go to a significant portion of what's happening outside (which is almost always hundreds of micrograms, sometimes thousands), and no purifier can beat that. Maybe if I put ten of them in a row, but it's expensive and noise will be unbearable.

[robga]

I have 2x 400m3 CADR purifiers and 4x AirGradients to monitor to Home Assistant. But I live in a fairly clean air city. It’s the pollen count that can be high. I suppose my point was I often trade going from 0 to 6 PM2.5 to reduce CO2 from 1200 to 600 for a while. Whether or not that is smart is one for the jury.

[Traubenfuchs]

May I ask what you use to measure particles in air?

All I seem to find are either amazon frauds/scams or overprized professional grade meters.

[5e92cb50239222b]

Sorry, probably not much help from me here. I've been using DIY stations thrown together from ESP32 development boards and low-cost Plantower sensors (PMS5003 and PMS7003). They're surprisingly accurate — my measurements over the past three years closely match the official government data (which is collected using calibrated "professional" air quality stations priced at $10k or more).

It's cheap, but you have to do everything yourself. A friend of mine did something similar, but using ESPHome and Home Assistant, and I think he didn't have to write any code at all, just a bit of YAML to tie it all together.

https://github.com/esphome/esphome

https://home-assistant.io/