# Purifying the same air hundrds of times - bad for air purifier? **URL:** \ **Category:** Factual Questions\ **Created:** [February 13, 2018, 11:52am UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756 "2018-02-13T11:52:42Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [February 13, 2018, 11:52am UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756/1 "2018-02-13T11:52:42Z")
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? ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [February 13, 2018, 12:03pm UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756/2 "2018-02-13T12:03:13Z")
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. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [February 13, 2018, 12:36pm UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756/3 "2018-02-13T12:36:02Z")
It’s just wear and tear on the fan motor bearings. ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [February 13, 2018, 1:51pm UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756/4 "2018-02-13T13:51:44Z")
What kind of purifier is it? ---
**Author:** ![Turble](https://avatars.discourse-cdn.com/v4/letter/t/8dc957/32.png) [@Turble](https://boards.straightdope.com/u/Turble)\ **Post date:** [February 13, 2018, 3:54pm UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756/5 "2018-02-13T15:54:48Z")
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/](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. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [February 13, 2018, 7:12pm UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756/6 "2018-02-13T19:12:45Z")
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. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [February 13, 2018, 7:39pm UTC](https://boards.straightdope.com/t/purifying-the-same-air-hundrds-of-times-bad-for-air-purifier/808756/7 "2018-02-13T19:39:02Z")
> [@Ruken](#): > > What kind of purifier is it? Envion Therapure 220H.