My office is a separate building adjacent to the house on its own traditional HVAC (heat pump) system. I only run it during working hours M-F and have a dehumidifier to manage humidity for when the system is off. All works fine.
Went into the attic to change the air filter and was surprised to see a patch of dampness / rusty, likely from the wire mesh in the filter being moist. Perhaps just condensation or attic humidity? The damp area is on the outflow side of the (horizontal) filter. Have never seen this before. Any reason for concern?
