Fourth Surface Low-E Coatings – A Prescription for ‘Pane’ But Not Without Side Effects

--by Jim Plavercsky
Door & Window Market Magazine

During my recent travels to Michigan with the Polar Vortex temperatures in full effect, it seemed as though every window company I was visiting was getting phone calls from angry and confused customers about condensation. It seemed like condensation complaints were on everybody’s mind. “Yes we like when the phone rings, especially this time of the year when sales are slow, but not to hear about condensation complaints! We want to be out selling more windows but it seems like we are driving around visiting angry and frustrated customers to investigate condensation complaints,” said one frustrated window dealer.

With outside temperatures hitting record lows and inside temperatures remaining toasty, the driving force for heat to escape across a window boundary is very high, and “heat goes from where it is hot to where it is not.”

As heat migrates from the inside of the window to the outside, the inside pane of glass becomes cooler than room temperature. Now take this situation and add in a fourth-surface low-E coating. Many window manufacturers are using this technology to achieve very low U-value ratings which they can post on their NFRC labels and consequently compete in a thermal performance league usually reserved for windows made with triple-pane insulating glass construction. As you know, the NFRC label is required to list the window U-value but Condensation Resistance (CR) ratings are optional.

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