ASHRAE Journal - March 2022 - 51

TECHNICAL FEATURE
of all insulated glass units (IGUs) sold for residential
windows. While low-e double-pane windows save
energy over non-low-e windows, additional room for
savings exists if higher effi ciency window options are
implemented. High thermal performance triple-pane
windows have existed in the U.S. market since the early
1980s, but adoption of the technology has been minimal,
and sales have never reached higher than 2% to
3% of market share despite accounting for nearly 1/3 of
products certifi ed by the National Fenestration Rating
Council (NFRC)2 (Figure 1), including product lines in
the Energy Star Most Effi cient program (U-factor ≤ 0.20)
made by over 43 manufacturers.
Previous studies by Lawrence Berkeley National
Laboratory have shown potential energy use reductions
of 16% in Minneapolis, 12% in Washington, D.C., and 7%
in Houston, when triple-pane windows are installed in
place of the typical double-pane Energy Star products
most commonly used today.1 This energy reduction
comes primarily from heating energy savings. Greater
energy savings are achievable by choosing glass coatings
specifi cally designed to optimize the solar heat gain
appropriate for each climate.
In addition to the energy savings and condensation
reduction potential of triple-pane windows, these
higher performing windows offer added benefi ts,
including increased occupant comfort by maintaining
warmer room-side glass temperatures (in cold climates)
and reduced sound transmission, both highly marketable
features for new construction and retrofi t markets.
High-performance windows are now in an ideal position
for widespread market adoption in both the new construction
and retrofi t markets.
When considering high-performance windows, the
incremental cost is always a top consideration. Window
prices vary signifi cantly and are infl uenced by many factors,
including framing materials, warranty, structural
performance, low-e coatings, grids, hardware, etc. While
the thermal effi ciency features contribute only a modest
fraction to window hardware costs, the retail price premium
to upgrade to triple-pane windows compared to
double-pane windows can be substantial (and variable).
In a 2019 builder survey conducted by Pacifi c
Northwest National Laboratory (PNNL), some builders
indicated that the price quote for triple-pane windows
was sometimes twice that of double-pane windows,
making the windows cost prohibitive in many cases.
FIGURE 1 Histogram of the number of models of window listings by type in the
National Fenestration Rating Council (NFRC) certified product database as of
July 2016.
500
400
300
200
100
0.11
Double-Pane Low-e
Triple-Pane
0.15 0.19
0.23 0.27
0.31 0.35
U-Factor (Btu/h·ft2·°F)
However, in that same survey several builders who have
focused on fi nding relatively lower-cost vinyl-framed
windows were able to fi nd a consistent supply of triplepane
vinyl-framed windows at a cost premium of only
30% over similar double-pane windows.3 Although
prices still vary considerably, recent market research
suggests that the incremental price between doubleand
triple-pane window product lines is narrowing.
The U.S. Department of Energy (DOE) has been working
with glass and window manufacturers to make
high-performance (0.20 U-factor or better) windows
more affordable by exploring cost optimized triple-pane
windows, including various confi gurations of thin-triple
windows (see " Thin-Glass, Triple-Pane Technology
Explained " sidebar). As part of the DOE's ongoing
High-R Windows fi eld validation testing program, a
series of thin triple-pane windows with a 0.2 U-factor or
better have been installed in fi eld sites across the U.S. at
incremental costs over standard Energy Star windows of
$6/ft2 ($65/m2) or less (Figure 2).
In terms of builder installation costs, these fi eld tests
confi rmed that this series of triple-pane windows could
be installed with no more than two installers, and the
labor and materials required were not notably different
than what would be required to install double-pane
windows. Multiple versions of the thin-glass triple-pane
IGU have been developed, NFRC certifi ed and released
into the market within the last year. Incremental
costs of $3/ft2 to $5/ft2 ($32/m2 to $54/m2) or less than
$100/window for triple-panes are available now, and
options will continue to grow as the market demand
expands.4
M A R C H 2 0 2 2 ashrae.org ASHRAE JOURNAL
51
0.39
NFRC Certifi ed Windows (Thousands)
http://www.ashrae.org
ASHRAE Journal - March 2022

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