Less than 50%.
My classroom has been at 85% or higher all year long. I have mold growing on cases.
If your room is too sticky, ask your HVAC services to adjust the flow rate or the frequency rate of the chiller system. They can do that, and increased air flow (processes more water out of it) helps a lot.
Ask your district when the last time the chiller filters were changed. In my district, it was 2 years between changes - the air wasn't being cleaned OR dried out. That contractor was fired ...
Ok...for all of my scientifically-minded band director friends who keep a watch on yours, what is your preferred humidity level in your band hall? Currently, mine is sitting at 69%. Music feels damp at times and the air is usually sticky. I know it's not good for the horns.
I'm just curious if I need to spend the $$ on a dehumidifier or two. I've had mildew issues ($1600 to clean and replace pads on 9 clarinets already) from AC being out for a few weeks in the summer (unknown to me).
I am going to purchase silica packs to put in all of the cases to hopefully help the issue.