The U.S. housing stock is aging. Almost 40% of pre-1990 homes contain heating systems that are more than twenty years old, making them ripe for deep retrofits. These retrofits could take advantage of right timing by improving the building envelope while replacing the furnace with a smaller, more efficient one.
For more information on right timing for retrofits, check out RMI's Retrofit Depot:
U.S. Energy Information Administration. 2010. Annual Energy Outlook 2010. Washington DC: U.S. Energy Information Administration, May 11. link