If you plan to use your air purifier in a medium (between 25 – 60 m2) or big room (> 70 m2), then you should aim for a powerful air purifier. A powerful air purifier can filter a higher volume of air, as it has a bigger filter and a faster fan.
Air purifiers for medium and big rooms tend to be more expensive than those that are for small rooms. The difference is that they need to be bigger, have a more powerful engine and more efficient filters, as they need to filter a higher volume of air. This increases the price. It also increases the size and the weight of these air cleaner.
On the other hand, these bigger air purifiers offer more features than the smaller, budget ones. For example some include germ sterilization with UV light ( UV Light Air Purifier : TruSens Z-3000 ), other include heating functionality ( Dyson Air Purifier: Hot + Cool Fan Heater AM09 ) , and so on.
See below a list with the most advanced air purifiers for medium and big rooms.