Homeowners typically consider replacing windows an obvious energy conservation measure and are surprised when an energy audit does not identify this renovation as a priority. While it is true that modern window technologies such as double-pane glass promise greater energy savings, the cost of quality window replacements is significant.  This means other energy conservation measures provide a much better value.

 
Generally, the most cost effective way to reduce airflow and increase the efficiency of a home is to air seal and insulate. Air sealing creates barriers to airflow by covering cracks and openings in the building cavity. Adding insulation on top of air sealing will slow heat flow and increase occupant comfort, as well as helping your home retain the air you have already paid to heat. If your home has its original wood windows, they should be retained. The quality of this old-growth wood and thicker glass cannot be replaced, and these windows were constructed in modular units for easy repair.  Retrofitting to reduce air leakage can be completed at a fraction of the cost of new windows. 

 
If window replacement is still a renovation you want to pursue, be sure to consider these factors:

 
Replacement windows are not “maintenance free” 
 
According to Michael Jackson, FAIA, chief architect of the Illinois Historic Preservation Agency pointed out, “maintenance free" means windows cannot be repaired. This truism is critically important when deciding whether to replace or restore. Vinyl, fiberglass and aluminum windows and insulated glass are formed using materials and techniques that by and large are not conservable. Once they deform, fade, warp or fail in other ways, there is virtually nothing that can be done but turn to replacements, perpetuating a cycle that repeats every 20 years.    
 
Consider storm windows
 
The payback time for adding a single-pane storm window to an existing single-pane window is 4 years. The payback time for replacing a single-pane window with insulated glass window is more than 41 years, and for replacing a single-pane window and storm with a low-e insulated glass window, payback estimates exceed 75 years. According to other sources, these payback periods are low – numbers closer to 100-150 years for payback are also sited.  
 
Environmental costs of window replacement   
 
A poorly performing window that requires replacement after just a few years means additional debris in our landfills, resources extracted for production and energy for manufacturing and transport, none of which is sustainable. The materials that comprise many replacement windows - aluminum, vinyl and glass - are among the greediest in terms of energy consumption, resource depletion and inability to recycle. All leave a heavy environmental footprint.