I ask the question because I am in the process of having my ductwork enlarged. The 0.5 max water column static pressure is what is listed on my nameplate and from what I can tell is the same max for many systems.
I have a new Trane 4-ton XL15i/ 100K btu-XV95 system in a 2800 sq. ft. 2-story home in NJ. With some key dampers closed the system works great but the static pressure is sitting at 1.1 with a new filter (positive =0.8 and negative = 0.3). I decided to have some ductwork done to get the SP down to nameplate or below to save some energy cost and not shorten the life of the motor.
My Duct guy said it is unrealistic for people in most homes to think that they can get the 0.5 SP or below. He said some want to get to 0.1 so they will only be using the "75 watt light bulb" amount of energy that the salesman sold them on. He said when you consider ~0.25 for the coil, ~0.2 for a good filter that only leaves you 0.05 for everthing else. He said it is no way that with grills, elbows, turns, etc. no matter how gigantic you make your ducts you will ever get the 0.5 or below value.
Do you guys agree with that? Or is it that my guy just does not know how to get there? Why would the manufacturers make 0.5 the max if it is unacheivable in most homes?