There are a variety of signals that all homeowners should be aware of, indicating that it is time to replace your existing windows or doors:
Increasing energy bills could indicate that your windows or doors are not fulfilling their role as thermal control mechanisms, either from loose frames or a lack of water/air tightness in insulation. Windows should prevent drafts and air leaks, and if either of those appear, it is time for a replacement.
Visual and aesthetic signals are often the most evident of all, including broken or cracked glass, peeling paint or frail and weakening aluminum. Rotting frames are also one of the best indicators, since a poor frame can dispel all the advantage of even the best-quality window, including superior insulation and security.
The formation of ice or frost on the windows signals condensation build-up from rapid changes in temperatures. This often occurs when low quality or weakened insulation and thermal materials allow air to infiltrate too quickly with rapid changes in temperature.
Poor operation can often signal issues with hinges or hardware, which in most cases can be eliminated with simply a hardware replacement; however, at times, poor operation can signal warping or bowing of the frame. Consult a professional installer for a recommendation for further action.