The primary goal of any new window installation is energy efficiency. But how do you know when to spend thousands to replace all your windows, rather than make a few minor repairs to achieve the same result? Decaying or rotting window casings need total replacement, as well as windows that don't properly open and close. Otherwise, weather stripping and caulking can be applied to increase energy efficiency. Budget tip: Visit Homewyse.com to estimate the average cost to install replacement windows in your ZIP code.