Myth #1: Closing the Vent Saves Energy
Though it seems that closing vents in unused rooms would save energy, the energy consumed by the system is at the unit itself, and restricting conditioned air at a vent termination redirects it to other locations in the house or through leaks in your duct system. Closing vents also puts backpressure on the fan that pushes the air through the system, causing it to work harder, use more energy, and wear out faster.
Myth #2: New Windows = Significant Energy Cost Savings
Replacing single-pane windows for Energy-Star rated dual-pane windows will save energy. That energy savings, however, is a function of the size and number of windows in your home, their orientation and overhangs, and the location of your house and the climate zone you are live in. This typically amounts to a small fraction of your total energy use, and given the expense of replacing windows, there are typically much more cost-effective ways to reduce your energy bills.