I have a friend with an 18 yr old horz gas furance connected to 20"s of duct,connected to a 6 yr old horz coil connected to the supply plenum. The fan is blowing water off the coil and into the supply plenum. Is this a common problem? And what do you do about it. No the pan is not leaking. The water is being blown past the pan about 3/4" to 1".