I'd never use one. I don't remember exactly what we had at my work, but when a good friend of my boss saw it he freaked and told us to unplug it right away. I can't remember what he did for a living, but he knew a lot about them and gave us a ton of literature on ionizers. I'll have to see if my boss still has the info he gave us. He said that ionizers released ozone into our atmosphere, where it should not be. Yes we already have some ozone in our atmosphere, but ionizers release much much more then people should have contact with. Over time ozone exposure can cause health problems in people and pets. My boss has asthma and she was having a lot of problems, almost as soon (with in a day) after we turned off the ionizer she felt so much better and didn't need to use her inhaler near as often. He said it can even kill small pets. They also take the dust from the air and push it against your walls and furniture causing them to become really dusty and dirty.