Metric 0 of air device purchase is the square footage of the room being served. If you are using it in one room WITH THE DOOR CLOSED, then you measure the room and provide the square footage. If you are using it in an open door area, you need one that can cover the entire area....so if its in the living room and you have a 2500sq ft house with all the doors open you need a 2500sq ft capable unit.

https://austinair.com/ is the king, but you have to buy the right size and/or buy a couple to make up the right size.

If you aren't super concerned on air quality and have a price ceiling: https://www.youtube.com/watch?v=kH5APw_SLUU