I live in a 911 sq. ft apartment on the top floor of my building. I bought two Alen BreatheSmart 45i air purifiers: 1 for my bedroom and 1 for my living/kitchen/dining open concept area. I LOVE the Auto status of detecting air pollutants and increasing the speed. A perfect example of how well the auto feature works- I was getting ready for work and I put on spray deodorant. As soon as I walked into the bedroom to get dressed, I saw the light on the air purifier change from blue, to green, then yellow, then red! I was in shock at how fast it picked up the air sample and eliminated the pollutant from the spray. I have terrible allergies so I had done a ton of research and identified that Alen is by far the best air purifier that money can buy. You most definitely get what you pay for! You won't be disappointed!