There are a few things to consider when purchasing an air purifier. The size of the room, the type of filter, and the noise level. The size of the room is important because the larger the room, the more filters will need to be installed. Additionally, the more filters there are, the more likely it is that one will need to be replaced. The type of filter is also important. A high-quality filter will remove more pollutants than a low-quality filter. Additionally, a high-quality filter will be more expensive. The noise level is also important. A high-quality air purifier will be quieter than a lower-quality air purifier. Additionally, a high-quality air purifier will have a longer life.