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Interior Storm Windows

Increase energy efficiency and maintain exterior aesthetics

Find manufacturers of this PATH Technology Inventory item

Homeowners are usually interested in lowering energy expenses, but are not always willing to pay large costs or sacrifice the appearance of their home to do so. Interior storm windows provide a compromise by increasing the energy performance of Interior storm windows improve efficiency without altering the home's exterior appearance a home at significant cost savings over window replacement. They are particularly suited to historic and other homes where it is desirable to retain the original windows or to improve efficiency without altering the home’s exterior appearance. In addition to energy benefits, interior storm windows can improve sound resistance, decrease window condensation, and reduce degradation to furnishings from ultraviolet (UV) light.

Tight-fitting interior storm windows can reduce drafts, thereby improving comfort. By creating an airspace between the interior and exterior windows, they also improve the insulating value of the window assembly and raise the interior window temperature (hence also improving comfort in addition to reducing energy bills). One field study of interior storm windows at three Florida residences reported heating and cooling energy savings of 29 percent and noticeably reduced interior window condensation.

Interior storm windows can function in place, year-round, or can be removed from windows for ventilation during milder weather. They can also be customized to fit any size rectangular window and some manufacturers advertise the ability to fit a variety of geometric shaped windows. Interior storm windows generally have mounting brackets made of vinyl or metal that are permanently fastened to one or more sides of the interior window frame, and detachable glass or acrylic panes. The transparent pane commonly incorporates a magnetic strip for easy attachment to the bracket. Panes are also available in low-E glazing to resist heat gain and in UV-resistant glazing to reduce UV damage to interior furnishings.

Interior storm windows must be removed for natural ventilation. Interior storm windows with acrylic or polycarbonate glazing need extra care to prevent scratching or clouding. The seal around the perimeter of the interior storm window must be maintained for effective sound and thermal insulation. A magnetic seal may deteriorate over time and allow condensation to form on the interior surface of the storm window.


Interior storm windows cost less than replacement windows and reduce utility bills for the occupants.

Energy Efficiency

Interior storm windows reduce drafts and improve the insulating ability of a window assembly.

Quality and Durability

By raising the interior window temperature, interior storm windows reduce the likelihood of condensation on windows, thereby reducing maintenance needs.


Interior storm windows are available directly from the manufacturer or through local distributors throughout the United States.

Interior storm window "do-it-yourself kits" sell for as little as $55 for a 60"x 30" window. However, larger custom windows can sell for more than $200 installed. When looking to improve energy efficiency, adding interior storm windows is a less costly option than complete window replacement.

Utility cost savings will depend on the efficiency of the original window assembly versus the efficiency of the assembly containing interior storm windows.

Manufacturers of interior storm windows use materials permitted by most building codes. Windows are also available in tempered glass and acrylic to meet impact resistance requirements for certain installations.

Not Applicable

Interior storm window installation varies by manufacturer, but most can be mounted on the inside of window jambs or flush to the window molding. They are also capable of being mounted on flat or angled surfaces, and can be customized at the factory. Authorized dealers or contractors may be needed to install some interior storm windows. Some producers sell kits to contractors and homeowners for self-installation.

Warranties vary by manufacturer, but commonly last between 5 and 10 years..

Interior storm windows can be used in historic homes, because they have little effect on interior or exterior architecture. Interior storm windows can reduce drafts and increase the overall thermal insulation of the window, providing energy savings during heating and cooling seasons. Interior storm windows can also reduce exterior sound transmission through windows. Many manufacturers offer interior storm windows with UV protection, which reduces the amount of UV rays transmitted through the windows. Storm windows mounted on the interior can reduce condensation on windows during cold weather by raising the temperature of the interior glass.

Interior storm window "do-it-yourself kits" sell for as little as $55 for a 60"x 30" window. However, larger custom windows can sell for more than $200 installed.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.