For the best possible results, it is highly recommended to keep your air purifier running 24 hours a day. The energy cost of most air purifiers is minimal, and leaving the machine on for extended periods of time poses no real danger. This is especially true in homes with a lot of contaminants or if you have asthma or allergies. If you prefer to turn the unit off overnight, then running it for a few hours at the highest setting or up to 12 hours a day should be sufficient. In summary, it is recommended to run your air purifier unit for at least 12 hours a day.
This is a good rule of thumb. Of course, it's okay if you don't follow this schedule every day, but keep in mind that the more you use your air purifier, the fresher and cleaner it will be all year round.
