Energy Efficient Windows
High performance windows with new glazing technologies not only reduce energy costs but make homes more comfortable as well. During cold weather, exterior temperatures drive interior glass surface temperatures down below the room air temperature; how low the glass temperature drops depends on the window’s insulating quality. If people are exposed to the effects of a cold surface, they can experience significant radiant heat loss to that cold surface and they feel uncomfortable, even if the room air temperature is comfortable. When the interior glass surface temperature is 52°F or less, it is most likely that there will be discomfort. During warm weather, solar radiation can cause discomfort. Just as people turn up the heat to compensate for cold windows in cold weather, they may use air-conditioning to counter the effects of warm window surfaces and sunlight in summer.
High-performance windows create warmer interior glass surfaces, reducing frost and condensation. High-performance windows with warm edge technology and insulating frames have such a warm interior surface that condensation on any interior surfaces is significantly reduced under all conditions. Condensation occurs when the interior surface temperature of the glass drops below either the dewpoint or frost point. A window’s frame and/or glazing system can contribute to the possibility of condensation if they are poor performers for a specific climate. High-performance windows create warmer interior glass surfaces, reducing condensation and frost.
The interior humidity level can be a contributing factor, reducing interior humidity is an important component in controlling condensation. If necessary use vent fans, dehumidifiers, and/or air-to-air heat exchangers to help control a home’s humidity levels.
In climates that mainly require cooling, non-energy efficient windows can be a major source of unwanted heat gain. In recent years, low-E coatings that reject solar heat without darkening the glass have undergone a technological revolution. It is now possible to significantly reduce solar heat gain and improve comfort while providing clear views and daylight.
In climates with a significant heating season, non-energy efficient windows can represent a major source of unwanted heat loss, discomfort, and condensation problems. In recent decades, windows have undergone a technological revolution. It is now possible to have lower heat loss, less air leakage, and warmer window surfaces that improve comfort and minimize condensation. Depending on the condition of the old windows in an existing home, the savings can be higher if window replacement leads to long-term air leakage reduction.