Parts of my home are cooler than others. I have vents in every room but they do not all preform equally well. How can I direct the heat to where I need it most while not overheating other rooms?

There is a science to the duct work in a furnace distribution system. For instance, if you vent a duct off the end of a plenum you will get more heat than taking the same vent off the side of the same plenum line. This is usually not something you have control over so...