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Can I install a storm window over my vinyl window to achieve better thermal efficiencies?

12/1/2010 - Kevin A. Seiling - V.P. of Engineering VEKA Inc.

VEKA Commentary on the use of Secondary Storm Windows Installed over Prime Vinyl Windows: Secondary storms are intentionally designed to allow greater amounts of air and water infiltration. This is done to insure proper ventilation and drainage so that condensation between the storm and prime are minimized. Proper drainage is also important to reduce the risk of puddle water which may support the growth of mold. Several factors must be considered before installing a secondary storm window over a prime vinyl window. In rare cases, heat buildup between the storm and the prime can be such as to cause the vinyl frames and or sashes to sag, warp, twist, or bow.

The potential for excessive heat buildup may be exacerbated by the type and reflective properties of interior window treatments. Avoiding southern and western facing exposures with direct sunlight would be wise. A thorough inspection after installation is recommended to insure weep holes are clear to allow proper drainage and ventilation. Very few if any studies have been conducted to determine the effects of storm products installed over today’s high performance glazing vinyl windows. Therefore, Veka does not recommend applying storm windows over prime vinyl windows.


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