Energy Efficiency

The following statement is from A Comparative Study of the Cumulative Energy Use of Historical Versus Contemporary Windows (PDF) written by  Frank Shirley, Fred Gamble and Jarod Galvin from December 3, 2010:

“This study compares the life-cycle costs of two residential window systems in a pre-1940 house in Boston, Massachusetts. One is an original double-hung window with a new triple-track storm unit. The other is a new, vinyl, double-hung replacement window. Our results are obtained from an algorithm that yields the total present value of all costs associated with a window system over its entire life, including acquisition, installation, maintenance, and energy. 

Our study provided 2 notable findings: 
  1. the thermal performances of the two-window systems are similar; and
  2. taking all costs into account, it is more cost effective to add a storm window to a historical window, and it remains so at all times for the full 100-year life we considered.”
Additional Resources
A new study shows that restored 200-year old windows are as airtight as brand new replacements, which compared two new windows against two restored windows for air infiltration (the biggest source of heat loss with windows).

Green America: Three Steps to Super-Efficient Windows

This Wasteful Old House - New York Times Opinion by Richard Moe

Testing the Energy Performance of Wood Windows in Cold Climates - National Center for Preservation Technology and Training

Saving Windows, Saving Money: Evaluation of the Energy Performance of Window Retrofit and Replacement - Preservation Green Lab from the Preservation Leadership Forum

Repair and Upgrade Windows and Doors - Techincal Preservation Services of the National Park Service

Focus on Weatherization is Shift on Energy Costs - New York Times

Historic Windows and Energy Efficiency - Environmentally conscious historic homeowners can keep their historic windows and improve energy efficiency at the same time.