Venta humidifiers clean and humidify the air in one step. That is why they are also called air washers. I have been using Venta humidifiers for over 15 years and can thus bring the humidity in my house from 25% (without humidification) to around 45%. For this I need 3-4 LW45 humidifiers. Depending on the winter (cold or not so cold)

The colder outside, the more it has to be moistened. Because the more heating power per dryer it gets.