Entrance systems with clear or decorative glass are great ways to bring more natural light into the home and increase curb appeal. Full size doorglass maximizes natural light while meeting energy efficiency criteria. Door and window thermal performance requirements have been defined through a partnership between the Department of Energy (DOE) and industry. Thermal performance is defined by two key values: U-factor and solar heat gain coefficient.
This is a measure of overall thermal transmission. The lower the U-factor, the slower the rate of heat flow into or out of the house. This can mean lower heating bills in the winter and lower cooling bills in the summer. Full-size doorglass systems meet U-factor criteria even for northern climates.
Solar heat gain coefficient (SHGC)
This is a measure of the portion of directly transmitted and absorbed solar energy that enters the interior of the home. The higher the SHGC value, the higher the heat gain. Higher solar heat gain may be desired in colder climates during the winter. Lower solar heat gain translates into lower cooling needs during summer months. Full-size doorglass systems meet SHGC criteria even for Southern climates.
Thermal performance standards, as defined by the DOE, vary by region of the country. The map below shows the four U.S. climate zones. The table shows the maximum U-factor and SHGC for each zone.
ODL glass can be used in doors to meet DOE thermal performance criteria.
The window & door industry has standardized methods using computer simulation and lab testing to establish ratings for different product configurations. Independent test facilities have used ODL doorglass used to develop the performance ratings above through simulation and product testing. The values presented above are for full glass used in different door constructions. Smaller glass sizes result in even lower values.
Thermal Performance by Door & Glass Type
Note that local and state codes use DOE standards as a guideline but may be more or less stringent. Your builder will understand the entry system construction appropriate to meet the thermal performance needs of the local market.
Low-e glass is made with an invisible high-performance coating that blocks heat flow. Low-e coatings are very popular in windows as they are needed in many regions to meet DOE thermal performance criteria. If low-e coatings are used in windows, it is very common that they will also be used in adjacent doorglass.
Integral Treatment Doorglass
When fully open the U-factor and SHGC values for doorglass with Integral blinds and shades are similar to clear doorglass. However, because you can control the amount of light with these products the SHGC and U-factor values can be lower based on how you choose to operate them. They are a great option for situations where you still want to bring natural light into a room but want more privacy. They have the added benefit of eliminating dusting so they are a low maintance solution as well.
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