All water pipes in my two story house are under the first floor and in the first floor walls to the height needed to supply water to faucets in kitchen and bathrooms in the first floor. This morning when in bathroom (first floor) water dripped on my head; I looked up and the ceiling around the air duct for heat and A/C was soaking wet as was the metal vent itself. The inside component of the heat pump is on the second floor in crawl space. Thedrain pipe for condensation from it is between first and second floor. Problem does not exist in any other ceiling vent area. What could be going on?