Windowtherm is a lightweight interior panel system that improves the thermal performance of windows by insulating the glazing and air sealing the opening. In heated spaces, Windowtherm prevents conductive, infiltrative and radiant heat losses, thus raising the temperature of the room and improving comfort immediately. The product works the same way to improve energy performance in cooled spaces during cooling seasons. 

Windowtherm is custom fabricated from gasketed, extruded aluminum frame rails with retention grooves to hold two sheets of polyolefin film using spline. Open-cell weather-stripping is attached to the mounting surface.  Extruded aluminum muntins are used for dimensions beyond 48” for panel stability. The product is a lot like a screen door panel, except it has film instead of screen material that is mounted on BOTH sides of the frame to form an airtight gap. The Windowtherm is mounted on the interior surface of window assemblies to dramatically reduce heat transfer and air infiltration. 

Windowtherm can be fabricated for curved shapes, making it one of the only thermal improvement options on the market for stained glass and other custom window forms. 

The result is significantly improved comfort and significant lower energy usage for heating and cooling. Simplicity of installation makes it a cost-effective alternative to window replacement. 

In older buildings where replacement of historic windows is difficult or cost-prohibitive, Windowtherm’s superior air sealing can improve the building envelope’s thermal performance even more than added R-value. Stopping air infiltration reduces the total volume of air that the building’s HVAC system has to heat in the winter – or cool in the summer. Drafts due to air movement are reduced, and convective drafts attributable to cold glass are eliminated. 

NFRC testing has shown Windowtherm to raise the R-value of a window by more than 2 hr-ft2-°F/BTU, and to significantly reduce air infiltration at windows. The result is a draft-free window installation, and a window surface that is warm to the touch all winter long - regardless of the outdoor temperature. 

NYSERDA testing before and after Windowtherm installation showed a 30% reduction in heating demand. Utility companies and MA have provided rebates based on projected fuel savings. Our ongoing blower door testing program continues to demonstrate the air sealing effectiveness of Windowtherm on different types of buildings of all different ages and conditions. 

Every building is different, and it’s typically cost-prohibitive to establish the baseline thermal performance of a building, so it’s typically not possible to calculate energy savings due to Windowtherm in advance. If the building is in a climate that experiences summer and winter extremes, here are a few rules of thumb you can use to assess Windowtherm’s suitability for your situation. 

• Windowtherm adds about R2 to any window. If poor performance windows are a large proportion of the building envelope area, consider Windowtherm.

• If most of the air infiltration at the building envelope is due to the windows, Windowtherm will significantly reduce heating and cooling bills.

• Windowtherm is great for historic windows: it gives single pane units superior thermal performance at a fraction of the cost of a replacement project.

• Windowtherm is most cost effective when the cost of pre-installation trim modification is negligible or relatively low.