Sizing a system is not simply a process of measuring the volume in a building.
Proper sizing includes measuring the length and size of duct runs.
I think that all trades people have heard the term static pressure' at one point or another but when one sees installations that resemble the anatomy of some deep sea creature, it becomes clear that there are many contractors that simply do not understand the effect. Homeowners are a group that often knows enough to ask some astute questions but do not grasp the concept of issues like static pressure. No doubt many of you have attempted to explain why using rigid ducting is better than flex but as soon as you begin to talk about inches of water column the homeowners eyes glaze over and they run for cover. The next time you find yourself in a situation where you need to make clear to either a homeowner or a fellow trades person what static pressure means, give the following explanation a try. Imagine your duct system is like the highway system.