I bought a rather powerful air purifier and put it in a small room and had it set to run. Quite a few hours later, it occurred to me (as I woke up from sleep) that by closing the room door, this meant that the purifier had simply been purifying the same enclosed air over and over again - in fact, possibly over 100 times, according to the advertised specs. I’m wondering if that is bad for the purifier machine in any way, or it just means I’ll have super-clean air to breathe in that room?
The latter. Purify is a silly word. They are filters. Once they get the dust/pollen out of the air they are essentially idling. You will reach a steady state of particles in the air, and stay there. Leaving the door open means a constant supply of more particles, a poorer steady state and the filters clog up sooner.
It’s just wear and tear on the fan motor bearings.
What kind of purifier is it?
You generally want three to six ACH (Air Changes per Hour) for general home use – maybe more in the case of severe allergies or other specific problems. Chemical labs and hospital operating rooms might look for around 25 ACH.
Here’s a site with a brief explanation of ACH:
https://www.achooallergy.com/learning/air-exchanges-per-hour-recognizing-air-purifier-marketing-ploys/
Those things are designed to run continuously for years. My Austin Air is 12 years old.
If you bought a stronger unit than you need you might try running it on a slower speed.
Air is entering the room through cracks around the door. (And possibly around the edges of the window, depending on how tight the design is.) No normal room in a house is sealed and you wouldn’t want it to be in the first place.
Envion Therapure 220H.