Energy models apply the laws of physics, but the hazy laws of human behavior might be behind the surprisingly good results found in recent independent tests of a retrofit window insulation product from Portland, Oregon-based Indow Windows.

Portland State University’s Green Building Research Laboratory has completed testing Indow Windows and reported some surprising results. ┬áThe insulating retrofit inserts saved 20 percent of the pilot homes’ heating bills.

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Instruments on an Indow Window in an insulated test enclosure at the Green Building Research Laboratory of Portland State University.
Instruments on an Indow Window in an insulated test enclosure at the Green Building Research Laboratory of Portland State University. GBRL performed laboratory testing, pilot home measurements, and whole-building energy simulation. The test was funded by Oregon BEST. (PSU GBRL photo)

“If you do a whole-home weatherization, the average savings is around 30 percent,” says Indow Windows founder and CEO Sam Pardue. “And that’s after spending $20,000 per home. Our inserts cost a quarter of that and deliver a big chunk of the savings. I hope that gets people in the energy efficiency industry to really sit up and take notice.”

What’s most interesting about the test results is that energy models predicted only 10 percent savings over single-pane windows. (This link leads to the report PDF.)

Energy models are not precise predictors of energy consumption, but when comparing building options the models rarely are off by so much. The lab report says a possible explanation for the higher savings is the increased comfort of occupants, which reduces their urge to turn up the thermostat. Without the radiant cooling effect of inefficient glazing, occupants feel warmer even though the room is the same temperature.


IN NOVEMBER 2010 Indow Windows launched its first product, a way to add insulating glazing without replacing single-pane windows typically found in older homes. The acrylic window inserts press into place on the inside of a window frame to reduce heat loss and provide better insulation than the single-pane glass, at a fraction of the price of replacement windows.

In two short years, Indow Windows has won awards including multiple Cleantech Open prizes, raised $1.3 million in Series A funding and expanded its distribution network. The company now has 39 dealers in 20 states and is approaching the $1 million revenue mark. It introduced an acoustic-grade version of its window inserts, which are beneficial for their noise-reduction qualities and have generated interest from commercial customers.


THE SIMPLICITY OF an acrylic insert — basically an indoor storm window — belies the complexity of making them cost effective. Window frames in older homes rarely have perfectly square corners; many are skewed by age and settling. An installer must measure every window’s size and shape before ordering Indow Windows for a home. Indow Windows devised laser measuring technologies to capture the precise geometry quickly so it can be transmitted to the factory for custom fabrication. Installers need training to use the measuring tools correctly, so the company also developed online education tools to remove the barrier of training-related travel for new Indow Windows dealers.

Indow Windows is in the process of raising more venture capital to invest in scaling up operations and introducing more energy saving products to the market.

Indow Windows founder and CEO Sam Pardue demonstrates his company's retrofit window insulation product.
Indow Windows founder and CEO Sam Pardue demonstrates his company’s retrofit window insulation product.

“We’re planning to introduce a low-E Indow Window this summer, which will be important for opening up the southwestern and southeastern U.S. markets,” Pardue says. Windows with low emissivity, or low-E, have coatings that reflect radiant infrared energy, while allowing visible light through. Low-E windows are more energy efficient because they keep radiant heat on the side where it originates — inside in winter, outside in summer — rather than passing the heat through the window. The U.S. Department of Commerce Jobs in Innovation Accelerator Challenge is providing a $150,000 grant for product development and performance testing.


FOUNDER SAM PARDUE offers this advice to cleantech entrepreneurs, based on his experience on the startup fast track:

“Ask for advice sooner rather than later. A lot of entrepreneurs make the mistake of holding their ideas close to the vest out of fear that someone might steal them. In reality, once you get going you’ll be trying to raise money and telling everyone about your idea.”