We have finished moving into our new (to us, built in 1999) house and it’s super humid outside lately. Dew point in the mid 70s (F). The house has forced heating/cooling and it maintains the temp well, but it has been 60-70% relative humidity the whole time.
Today I realized that our furnace has an outside air intake duct on the return side and I don’t know if it has a damper of any kind on it. That would explain why during the intermittent fan cycles without the AC running the humidity rises.
I have seen no levers/knobs/controls of any kind on the intake duct. It is wrapped in thick and soft black plastic insulation. I see no sign of a power cable anywhere along the duct or at the wall where it penetrates to the outside.
Is there anything I might be missing to indicate this duct has a damper that I might be able to adjust?