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The thermal performance of windows is affected by the interior environment of the building, external weather conditions, and the way the window is installed. Glass choices and glazing options have a significant impact on thermal performance as well. In addition, window frame modifications can be made. These "thermally improved" frames incorporate one or more thermal breaks, also known as thermal barriers.
A thermal break is defined as a material with low thermal conductivity placed in an extrusion with the purpose of reducing the flow of thermal energy (heat).
In aluminum windows, three types of thermal breaks are used. A standard pocket thermal break has been used in the window industry for decades. During manufacturing, a polymer much like epoxy is poured into a pocket in the metal extrusion. After the polymer solidifies, a specialized saw cuts through the pocket wall of the entire length of the extrusion to "debridge" the interior and exterior sections. This process is known as pour and debridge.
Deeper poured and debridged pockets increase the thermal efficiency of the window. However, there are structural limitations to the size and depth of the pocket.
More recently, a different type of thermal break has been used to enhance thermal performance beyond the capabilities of poured and debridged pockets, albeit at a higher cost. This process uses polyamide strips with very low conductance and relatively high structural strength. Using specialized equipment, the strips are "stitched" into slots in the extrusions.
In addition to having double or triple insulated glass, along with other performance options such as Thermal low-E, E+, tinting, or argon gas, a Thermal Barrier window offers another important benefit. The window frame and sash frames are insulated against heat and cold conduction. This is done by separating the outside metal parts from the inside with polyurethane, greatly reducing the amount of heat or cold transferred through the frames. This is known as a thermal break or thermal barrier.
The outside of the frame rests on dry ice at 109 degrees below zero. Humidity in the air freezes to that part of the frame, but the cold does not penetrate the Thermal Barrier.
Thermal Barrier windows are manufactured from close-tolerance aluminum extrusions. They have lower air leakage and much better resistance to heat transfer than single-paned windows. Thermal Barrier aluminum window performance is equal to or better than wood or vinyl windows.
Thermal Barrier aluminum windows are tested to strict industry specifications. Air leakage with a 25 MPH wind blowing outside cannot exceed 0.375 cubic feet per minute (CFM) for every foot of weatherstripped window perimeter. Our Series 700 Double Hung allows only 0.15 CFM air infiltration. Old windows often have rates of 1.5 or more, 10 times the air leakage of our Thermal Barrier aluminum windows!
There is no such thing as a condensation-proof window. Even walls will "sweat" when humidity is too high. Windows do not cause condensation; they simply prevent moisture from escaping and provide a surface that allows condensation to be readily seen. If inside glass and frame surfaces on a Thermal Barrier window show excessive moisture, you can be sure that moisture is also present in your walls and ceiling. (Click here for much more information on the causes of condensation and ways to eliminate it).
The maximum recommended interior relative humidity ranges from 15% at -20F to a maximum of 40% at +30F (see the chart below). Many homes have been built "tighter" to conserve energy, trapping indoor humidity. The best way to handle high indoor humidity is to vent it to the outside. Bathrooms, kitchens and laundry areas should be vented with a fan, or by opening windows slightly when the areas are in use. If that does not help, a dehumidifier might be necessary.
