Jim:

I didn't read all the other posts in this thread, but I can think of at least two reasons why a previous home owner would have secured the fire place flue dampers open:

1. Dryer exhaust duct is clogged with lint. Clothes aren't drying properly. Home owner misdiagnoses the problem as being insufficient make-up air coming into the house to replace warm moist air being blown out by the dryer. So, he opens the flue vents to allow for more made-up air.

2. Thermocouple on water heater is old and barely producing sufficient voltage to keep safety valve on gas valve open. So, pilot light flame going out, heaving home owner constantly running out of hot water. Home owner misdiagnoses the problem. He figures that when the dryer is operating, the make-up air is coming down the water heater flue and blowing the pilot light out. So, he opens the flue vent to allow make-up air to come in through the fire place instead.