The Dubious Benefits of Foam-Filled Vinyl Windows
Some manufacturers of vinyl-framed windows inject urethane foam into the hollow
vinyl frame to improve thermal performance and/or increase rigidity. Although a foam-filled frame is visually impressive when viewed from a cross section, the actual benefits in terms of energy performance are apparently minimal.
As part of a recent research project, Enermodal Engineering of Waterloo, Ontario, modeled the thermal performance of vinyl frames with and without foam insulation. The R-value of the hollow frame was R-2.0; the foam-filled frame was only slightly higher - R-2.3. IN a climatic region with 6,000 degree days per year (Denver, for example), that boils down to energy savings less than 50,000 Btu per window per year - about 30 cents' worth of natural gas heat.
Impact on overall window R-value
When installed in a double-glazed window with low-E glass, the slight
improvement in frame R-value produced by foam filling has little effect on
overall window R-value. Using the WINDOW 4.0 computer program developed by Lawrence Berkeley Laboratory, we calculated the overall R-value of vinyl windows with and without foam filling. The results show only 0.1 improvement in R-value.
The figures are theoretical calculations, but at least one laboratory measurement bears them out. Quality Testing Inc. of Everett, Washington, ran a series of tests on vinyl windows with and without foam filling. The results were very close to the theoretical results.
