Extremely loud! Best part of always turning it off. 
It looks great in our kitchen, which is why I bought this, I liked the design. But even in lowest setting it is so loud, like stressfully loud. We hesitate to use it actually and are always relieved when we turn it off. Not even convinced it’s super effective for how loud it is. I have an air purifier in the room that always detects poor air quality even when using this in the higher setting (which sounds a bit like a 747 taking off)