[wtcactus]

I'm not understanding if it also filters the outdoor air coming in.

I live in a place where supposedly the air is of good quality, and yet, when I open the windows, the all place gets a thin film of black dust on all surfaces - most probably due to the particle emissions and tire degradation dust from vehicles from the highway nearby.

The solution I've found is to open the windows every day for about half an hour and then put an air purifier to work.

[londons_explore]

it appears the air filter is an optional extra, but incompatible with the storm vent.

[open_erv2]

The filter is a bit messed up right now, you can put one on the TW4 but not the WM12.