Replacing single pane windows for energy star rated dual pane windows will save energy. 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.”
space heaters consume a lot of wattage to heat that very small space you need heated. Compared to the cost to heat the entire home you are losing the fight with the power bill.
“A home’s efficiency is less correlated to its age than to its design and construction. While many new homes are considered to be more efficient, there is often room for improvement and savings.”