Heating and Cooling supply vents
Heating and cooling supply vents are almost never installed right which is costing you money. The vent should be sealed off during construction to prevent debris from falling into the opening, but also for job site safety. This will prevent blockages in the duct from various debris to block air flow. It is common to find screws, wood, and drywall in duct work.
The vent should also be tied tight to the subfloor using mastic. This reduces the amount of air that will hit the bottom of the register and flow back down into the room above or below. This allows the air flow to get to the room it is intended to reach. In the average house 30% of the air leaks out of the duct work before it reaches the room it is intended to heat or cool. In a tight well designed duct system only 10% of the air leaks out of ducts.
Using hard duct as opposed to flex duct is another important strategy to getting the air to the room it is intended to heat or cool. If flex duct is required then limiting the bends in the design is important.