Two independent studies have shown Indow inserts are a high-performance, energy-saving solution that make existing windows more efficient. The inserts reduce energy use by increasing the thermal insulation of existing windows, completely blocking drafts and improving human comfort.

Because we created Indow to make the built environment more energy efficient and mitigate climate change, we deeply value this research. We’re also proud of the awards validating our work, including winning the national Energy Efficiency Award at the CleanTech Open and the Green Award from Door & Window Market Magazine for being an “Overall Energy Saver.”

The two studies were done by Portland State University’s Green Building Research Laboratory and the U.S. Department of Energy.

What was Involved in the Testing of these Energy-Efficient Window Inserts?

Green Building Research Lab director David Sailor spearheaded a study of four older homes with single-pane windows in the Portland, OR metropolitan region and also tested the inserts in a laboratory setting. His lab researches indoor and urban air quality, air pollution and sustainable buildings.

The pilot involved four older homes with single-pane windows. Researchers calculated air infiltration rates for each home and used infrared imaging to detect heat loss after installing the inserts.

In addition, researchers tested the U-factor in a lab setting to measure how well the energy-saving window inserts insulated single-pane windows. The lower the U-factor, the better the insulation. Researchers used Standard Grade inserts (⅛” thick) over mock single-pane windows inside a 6’ X 4’ plywood enclosure. The “inside room” temperature was kept at 70℉ and “outside” at 0℉. Heat transmission and loss were monitored with a hand-held Window Energy Profiler.

Impact of Portland State University’s Green Building Research Laboratory Study:

The testing showed Indow inserts lead to a nearly 20 percent reduction in energy use, considerably higher than the 10 percent reduction originally predicted by energy modeling. This is directly tied to the thermal comfort benefits: Indow inserts change the mean radiant room temperature by increasing the windows’ surface temperature. So not only do the inserts insulate against heat loss, people feel warmer standing next to acrylic than glass and are less likely to turn up the thermostat.

Oregon Public Broadcasting did a story on how PSU tested Indow inserts, which you can read here.

What was involved in the testing?

The Pacific Northwest National Laboratory performed the test for the U.S. Department of Energy. PNNL is a U.S. Department of Energy national laboratory and received the Office of Science’s highest performance rating according to DOE 2016 SC Laboratory Performance Report Card.

A Seattle homeowner installed window inserts for historic home energy efficiency of a historic home in all 27 windows. An eGauge energy meter monitored and recorded the energy use in the home over six months, with current transformers (CTs) placed over individual circuits to disaggregate the energy use.

Impact of Pacific Northwest National Laboratory Study:

The study added to a growing body of knowledge about the benefits of installing interior storms instead of replacing windows. It provided measurable energy savings and confirmed that inserts increase thermal comfort.

Indow’s Awards for Energy Performance:

CleanTech Open: National Energy Efficiency Award (2011).

Green Award from Door & Window Market Magazine for being an “Overall Energy Saver” (2014).

Edison Awards: Bronze in Energy Efficiency category (2011).

Additional resources:

Interior storm windows are widely recognized as a tool for making existing windows energy efficient. This saves waste by keeping windows out of the landfill and also helps preserve the value of historic structures. You can read more about the value of storm windows with the following resources:

Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement by the National Trust for Historic Preservation’s Preservation Green Lab.

Attachments Energy Rating Council

Removable Interior Storm Windows from the Building America Solution Center at the U.S. Department of Energy.