The Case for Triple Pane Windows

I recently attended a building science symposium and thought I would share one issue that may be relevant to folks considering the installation of new windows. In one of his presentations, Dr. John Straube recommended installing triple pane/glazed windows with e-coatings as an alternative to less energy efficient windows. ?I wholeheartedly agree, but maybe not for the reasons you might think. ??

Many view the decision to install triple pane windows solely as an economic one. That is, what are the future incremental energy cost savings versus the higher up front capital costs - then make a decision solely on that basis. ?This misses an important issue - thermal comfort, which provides immediate and long-lasting benefits.?????????????

Less energy efficient windows have colder window surface temperatures that create two sources of thermal discomfort in the winter. ?First, people exposed to a cold surface can experience meaningful radiant heat loss to that cold surface and feel uncomfortable, even when the room air temperature is at normal levels.? This radiant heat loss is the reverse of the warm radiant heat you feel when near a hot campfire, but the principle is the same.

Convective drafts (not air leaks, which is a different issue) near cold windows are the second major source of thermal discomfort.? Warm air next to the window is cooled and drops to the floor. ?It is then replaced by warmer air from the ceiling, which in turn is cooled. ?This sets up an air circulation loop that feels drafty and increases convective heat loss. ?These cold temperature-induced drafts occur at the same time as radiant heat loss - compounding discomfort and effectively contracting the living area.? An additional benefit is less sound transmission, which is more of a benefit in noisy urban areas.

In the last year, a friend replaced all the windows in his home with double pane windows - rejecting my advice.? He and his contractor concluded triple pane windows were a “waste of money” - based solely on a financial analysis.? I concluded, I did not communicate well enough, so this post is an effort to better explain the case.

Long ago our society transitioned from single to double pane as the standard for windows. Dr. John Straube suggested we will look back in 5-10 years and wonder why triple pane windows were not considered the standard today - I agree. ?As the incremental cost continues to decline; the decision to choose triple over double pane/glazed windows with e-coatings will become even easier.