The noise really does matter
Our old fan was loud enough that we avoided using it. I wanted the next one to clear moisture properly and feel easy to switch on every day.
That’s how I ended up learning about sones. The lower the number, the quieter the fan should sound. It gave me a much better way to compare models than words like ‘quiet’ printed on the box.
Then there was CFM
CFM is the airflow rating, and the right number depends on the bathroom and its ductwork. I measured the room and checked the existing setup before choosing a rating.
My short shopping list
I put enough airflow, a low sound rating and sensible installation requirements first. A humidity sensor or timer could be useful after those basics were covered.