[robga]

> To have the air purifier work effectively you need to keep your windows and doors closed.

Isn’t it the case that you can open windows to the extent that the air purifier CADR can cope with the influx? Then they are still “effective”. The relative air quality inside and outside is also highly relevant. I say this as someone with AGs, since I frequently do this dance when CO2 rises.

[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/

[ravel-bar-foo]

Most indoor air purifiers have low purifcation thoroughput compared to the space they are designed for (30 min to 5% PM2.5 concentration migh be a typical filtration rate). If you model that as an exponential decay it's about 10% per minute, so a leak of unfiltered air which would replace 1% of room air per minute would result in a steady state of ~9% unfiltered air, or twice the contamination the filter was rated for.

[ahaucnx]

It really depends on the outside pollution levels. In our experience indoor purification reduction with air purifiers correlate with outdoor pollution levels. So if it's really bad outside opening the windows just a little bit will already let a lit of dirty air on with which the purifier might not be able to effectively cope with.