Best Windows for Passive House Glazings: Most Energy Efficient

Selecting the Best Windows for Passive House Glazings (Most Energy Efficient)

Triple-pane Fiber-glass Frame Cross-sectional View

Like many aspects of Passive House design and construction, the topic of selecting the best windows for passive house (most energy efficient windows) construction could fill volumes and, in my opinion, may be the single most difficult/complex building component of passive house construction to consider.

There are a good number of choices available for windows most suited for passive house construction.  Unfortunately, most of these windows are manufactured outside of the United States (and Canada). Until such time that changes, compromises will inevitably have to be made.

Varying Climate Zones in the U.S. Determine the Windows to use in Passive House Construction

To make the task of window selection even more challenging, here in the U.S., the Energy Star program for energy efficient windows has been inherently flawed.  Historically, the program has not properly taken into account the varying climate zones and their impact on appropriate window thermal performance and has even encouraged the use of less than optimal glazings (with tax incentives) than what would otherwise be superior for a given climate zone.  Could there be a bit too much lobbying influence from the U.S. window manufacturer industry going one here?

There are a number of characteristics of windows which impact the overall energy efficiency of a window that should be examined and understood within the context of the construction site and some of them on the surface may appear to contradict one another.

Passive House Windows Energy Efficiencies versus World Climate Zones

Selecting the best performing windows for passive house will require a careful examination of the following.  The first three items listed below are the most important as they represent the culmination or end-result of the others.  The sixth item is critical to in the selection of the proper performance ratings of the first two (u-value, SHGC).

• Thermal insulating performance (as indicated by u-value)
• Solar heat gain coefficient (as indicated by SHGC)
• Airtightness
• Exterior Wall Orientation (relative to the sun)
• Visual transmittance (VT)
• Location of construction site (in terms of climate zone).
• Frame materials & construction
• Window opening type(tilt-and-turn, casement, awning, single hung, double hung, etc.)
• Number of window panes/glazings encased
• Glazing (Window) orientation
• Window size
• Glass coating material (low-e)
• Spacing (volume) between glass panes
• Thermal spacers used
• Type of glass pane set and mounting/setting within frame

I will address the more salient aspects of window energy efficiency in subsequent articles and hope to "shed light" on this complex topic for others considering which manufacturer/brand to select.