High-performance storm windows are a lower-cost alternative to window replacement and can save significant amounts of energy.
Windows are a major source of heating losses and gains in the building and can significantly drive up energy bills. Window replacement is not an option for many homeowners, whether the cost is too high or because they want to keep the historical integrity of their homes. Low-E storm windows can provide a cost-effective alternative to replacement; in particular, for moderate and low-income households. DOE has supported technology development, market assessment and early deployment of low-E storm windows through a variety of research, including climate-based modeling and field lab tests.
Before replacing sound windows, compare the cost of improving them with low-E storm windows. Original article photograph.
Historical context: the original 2015 article illustrated a housing stock with 41.8 percent single-pane, 56.8 percent double-pane and 1.4 percent triple-pane windows. These are not current national shares.
The PNNL Lab Homes Test
Building on previous research, the Pacific Northwest National Laboratory (PNNL) tested low-E storms on manufactured homes in 2013 and 2014 to determine the energy savings and payback periods. Side-by-side tests were conducted in two Lab Homes built in Richland, Washington. These manufactured homes were provided by Marlette, a manufactured housing manufacturer in Hermiston, Oregon. They were specified so that they would be representative of 1970s-era housing stock in the Pacific Northwest region. For example, insulation levels for floors, walls and ceilings were R-22, R-11 and R-22, respectively. The windows were double-pane, clear glass with aluminum frames. The performance of these baseline windows was compared to the performance of those same windows with exterior low-E storm windows attached, and to highly insulated windows retrofitted into the lab home. The May 2014 report provides the basis for revisiting those results today. Larson Manufacturing and Quanta Technologies supplied storm windows for the research.
Three Ways Low-E Storms Improve Windows
They can reduce air leakage around leaky primary windows; the improvement depends on the condition of the existing windows.
A low-E storm window creates dead air space, which reduces conduction and convective heat losses across the primary window.
Low-E glass reflects radiant heat back into the home.
Performance measures. Windows with low-E storms showed significant reduction in the U-factor and solar heat gain coefficient (SHGC). A lower U-factor means less heat transfer. The best SHGC depends on climate and orientation; lower solar gain helps in cooling weather but can reduce useful winter heat.
Whole-house energy savings. The low-E storm-window test yielded estimated annual whole-house savings of about 10 percent, compared to about 12 percent for triple-pane primary windows in a separate, similar Lab Homes test. These were annual estimates extrapolated from seasonal measurements, not guaranteed savings for every home. The low-E storm windows saw better savings in the heating season than the summer. The opposite was true for the highly insulated windows, because of their low solar heat gain coefficient. A 2016 research review explains the comparison.
Air leakage performance. The lab homes did not see a significant benefit from decreased air leakage because their baseline windows were already well sealed. Homes with leakier existing windows may see a different result.
This map from the original 2015 article illustrates climate-based storm-window selection. It is not a current price or payback guarantee. Select glazing for local heating and cooling needs; solar-control low-E glass limits summer heat gain.
Weep holes. For some experiments, weep holes at the bottom edge of the storm windows were temporarily sealed to see if this improved air leakage performance; results were not significant. In normal use, these openings drain condensation to the outside. Keep them open.
Peak energy use. During the heating season, the majority of savings occurred on sunny days at night, when it was the coldest outside. In summer, the greatest savings occurred on hot, sunny afternoons. This coincides with peak power periods for utilities, indicating that low-E storms can potentially decrease peak power use in the summer.
Cost and payback. The 2014 report estimated storm-window material costs of $1,354 to $1,900 for 196 square feet of window and patio-door area, for a simple payback period of five to seven years. Installation was excluded. The calculation assumed $269 in annual electricity savings at the 2013 national average rate of 12.12 cents per kilowatt-hour. Those are historical figures, not today's installed prices. For a current comparison, get an itemized quote for the openings you plan to cover, including installation, and divide that total by your estimated annual bill savings.
Window or general contractors can install low-E storm windows. Caulk and caulking gun, screw gun and measuring tape are common tools for screw-mounted exterior units; follow the instructions for the product and mounting method you choose.
An interior storm window adds a glazing layer while retaining the primary window. Current custom sizes and low-E options are available from specialty manufacturers; confirm the mounting method when ordering.
Measure the existing window opening. Exterior storm windows can be installed in two different configurations: an overlap installation or a blind stop configuration, in which the storm fits into the window opening. For a slider or any horizontal opening, measure the top, middle and bottom; use the smallest measurement, then follow the manufacturer's specified sizing allowance.
Dry fit the window by holding the exterior window up to the window opening and checking that the screw holes all land on solid wood. Make sure that the storm window and the primary window open in the same direction.
Caulk around the opening, then put the window back in place and screw it in. Caulk around the top and sides of the opening, but not around the bottom, as exterior storm windows have weep holes designed into the bottom. These help drain any condensation that occurs between the primary and exterior windows.
Blind stop installation can be used for interior storms. Typically, a trim piece is installed between the primary window and the interior storm window to ensure a good thermal break and sufficient air gap between the two windows. Follow the manufacturer's labels and instructions for low-E coating orientation.
Interior storms function as an air barrier. Seal around the opening using the manufacturer's specified caulk, weatherstripping or gasket system; do not assume every removable panel should be caulked in place. Maintain any required emergency escape opening.
Historical Lab Homes comparison retained from the original article. Storm-window seasonal results came from 2013–14 testing; annual results were extrapolated. The R-5 comparison came from a separate experiment. Key values are repeated below for easier reading on phones.
Estimated annual R-5 result, separate test: 1,784 ± 189 kWh; 12.2 ± 1.3 percent. Different baseline energy use means these percentages and kilowatt-hour totals should not be treated as a single side-by-side test.
Veteran journalist Matt Power has reported on innovation and sustainability in housing for nearly three decades. An award-winning writer, editor, and filmmaker, he has a long history of asking hard questions and adding depth and context as he unfolds complex issues.
Cost Analysis: Low-E Storm Windows
High-performance storm windows are a lower-cost alternative to window replacement and can save significant amounts of energy.
Windows are a major source of heating losses and gains in the building and can significantly drive up energy bills. Window replacement is not an option for many homeowners, whether the cost is too high or because they want to keep the historical integrity of their homes. Low-E storm windows can provide a cost-effective alternative to replacement; in particular, for moderate and low-income households. DOE has supported technology development, market assessment and early deployment of low-E storm windows through a variety of research, including climate-based modeling and field lab tests.
Before replacing sound windows, compare the cost of improving them with low-E storm windows. Original article photograph.
Historical context: the original 2015 article illustrated a housing stock with 41.8 percent single-pane, 56.8 percent double-pane and 1.4 percent triple-pane windows. These are not current national shares.
The PNNL Lab Homes Test
Building on previous research, the Pacific Northwest National Laboratory (PNNL) tested low-E storms on manufactured homes in 2013 and 2014 to determine the energy savings and payback periods. Side-by-side tests were conducted in two Lab Homes built in Richland, Washington. These manufactured homes were provided by Marlette, a manufactured housing manufacturer in Hermiston, Oregon. They were specified so that they would be representative of 1970s-era housing stock in the Pacific Northwest region. For example, insulation levels for floors, walls and ceilings were R-22, R-11 and R-22, respectively. The windows were double-pane, clear glass with aluminum frames. The performance of these baseline windows was compared to the performance of those same windows with exterior low-E storm windows attached, and to highly insulated windows retrofitted into the lab home. The May 2014 report provides the basis for revisiting those results today. Larson Manufacturing and Quanta Technologies supplied storm windows for the research.
Three Ways Low-E Storms Improve Windows
Performance measures. Windows with low-E storms showed significant reduction in the U-factor and solar heat gain coefficient (SHGC). A lower U-factor means less heat transfer. The best SHGC depends on climate and orientation; lower solar gain helps in cooling weather but can reduce useful winter heat.
Whole-house energy savings. The low-E storm-window test yielded estimated annual whole-house savings of about 10 percent, compared to about 12 percent for triple-pane primary windows in a separate, similar Lab Homes test. These were annual estimates extrapolated from seasonal measurements, not guaranteed savings for every home. The low-E storm windows saw better savings in the heating season than the summer. The opposite was true for the highly insulated windows, because of their low solar heat gain coefficient. A 2016 research review explains the comparison.
Air leakage performance. The lab homes did not see a significant benefit from decreased air leakage because their baseline windows were already well sealed. Homes with leakier existing windows may see a different result.
This map from the original 2015 article illustrates climate-based storm-window selection. It is not a current price or payback guarantee. Select glazing for local heating and cooling needs; solar-control low-E glass limits summer heat gain.
Weep holes. For some experiments, weep holes at the bottom edge of the storm windows were temporarily sealed to see if this improved air leakage performance; results were not significant. In normal use, these openings drain condensation to the outside. Keep them open.
Peak energy use. During the heating season, the majority of savings occurred on sunny days at night, when it was the coldest outside. In summer, the greatest savings occurred on hot, sunny afternoons. This coincides with peak power periods for utilities, indicating that low-E storms can potentially decrease peak power use in the summer.
Cost and payback. The 2014 report estimated storm-window material costs of $1,354 to $1,900 for 196 square feet of window and patio-door area, for a simple payback period of five to seven years. Installation was excluded. The calculation assumed $269 in annual electricity savings at the 2013 national average rate of 12.12 cents per kilowatt-hour. Those are historical figures, not today's installed prices. For a current comparison, get an itemized quote for the openings you plan to cover, including installation, and divide that total by your estimated annual bill savings.
Two current options are QuantaPanel 500 Series exterior low-E storm windows and Mon-Ray 500 Series storm windows, ordered with optional low-E glass. Both can improve existing windows without discarding sound original units. QuantaPanel also offers a 700 Series with a lower-profile design; it is an additional option, not a reason to replace a suitable 500 Series unit. Both manufacturers use project-specific quotes rather than a posted, standard installed price. Use QuantaPanel's residential quote form or the Mon-Ray product page's dealer and quotation contacts to price your sizes and glazing.
Installing Low-E Storms
Window or general contractors can install low-E storm windows. Caulk and caulking gun, screw gun and measuring tape are common tools for screw-mounted exterior units; follow the instructions for the product and mounting method you choose.
An interior storm window adds a glazing layer while retaining the primary window. Current custom sizes and low-E options are available from specialty manufacturers; confirm the mounting method when ordering.
Historical Lab Homes comparison retained from the original article. Storm-window seasonal results came from 2013–14 testing; annual results were extrapolated. The R-5 comparison came from a separate experiment. Key values are repeated below for easier reading on phones.
Updated content: October 19, 2026.
By Matt Power, Editor-In-Chief
Veteran journalist Matt Power has reported on innovation and sustainability in housing for nearly three decades. An award-winning writer, editor, and filmmaker, he has a long history of asking hard questions and adding depth and context as he unfolds complex issues.Also Read