My humidistat is broken. Both the new and old one are 3" vertical and 5" horizontal. There is a 5" vertical by 3" vertical hole in the ductwork, presumably from an even older humidistat. Whoever installed the current one covered the hole with duct tape, with a hole cut for the sensor. I was intending to do the same, but the new sensor is way over to the side and won't really work with the existing hole. (the old one has a sensor in the middle, so screws went on either side of the hole)
I have some aluminum flashing material. I'd like to put that over the hole with sheet metal screws, and seal the edges with duct tape. It is on the return, so there will be suction and cool air. Any problem with that idea? Obviously my HVAC knowledge is thin.