I have two furnaces in my house, using two separate duct systems in the attic. This is a one-story house. I checked the registers and found that the registers in one of the furnace systems have twice the air-flow than the registers in the others system.
I suspect that one or more of the ducts in the low-flow system may have opened up or may have collapsed. The ducts are the round, insulated flex-ducts type and are about 25 years old. The furnaces are new.
Beyond a visual inspection, which is difficult due to access problems, how can I determine if there are leaks in the duct system in the attic?