[tedd: explain the actual process of Duct Efficiency Testing in layman's terms, step-by-step.  explain it to an outside/observer/customer--not to a trainee]

Your duct system is like the home’s transmission.  The efficiency of the transmission, and proper match to furnace size, has a lot to do with the noise, comfort, efficiency, and life expectancy of your heating systems operation.

Like driving your car with the emergency brake on, if your heating system is too big for your duct work the furnace will tend to overheat, less heat will transfer through the heat exchanger to the household and instead will go out the exhaust.

Getting the smallest furnace possible (proper load sizing after home performance improvements) will usually make for the most comfort and lowest energy use.