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Double-Glazed, Clear Glass

A typical clear, double-glazed unit has two lites of glass with the inner and outer layers of glass both being clear and separated by an air gap. Double glazing, compared to single glazing, cuts heat loss in half due to the insulating air space between the glass layers. In addition to reducing the heat flow, a double-glazed unit with clear glass will allow the transmission of high visible light and high solar heat gain.

Center of Glass Properties

Note: These values are for the center of glass only. They should only be used to compare the effect of different glazing types, not to compare total window products. Frame choice can drastically affect performance. These values represent double glazing with a 1/2" air gap.

Whole Window Properties - Double-Glazed, Clear Glass
  Metal Frame Metal Frame Non-metal Non-metal
Frame Metal Frame Metal Frame with Thermal Break Non-metal Frame Non-metal Frame, Thermally Improved
U-Factor 0.71-0.99 0.56-0.70 0.41-0.55 n/a
SHGC 0.41-0.55 >0.60 0.41-0.60 n/a
VT >0.60 >0.60 >0.60 n/a
Note: The thermal performance properties of specific glazings and frames can vary depending on product design and materials.
The results presented here are averages. Consult specific manufacturers for NFRC rated U-factors and SHGCs for products of interest.

Double-Glazed, Tinted Glass

A typical double-glazed unit with bronze or gray tinted glass has two lites of glass with the the outer layer of glass being bronze or gray tint and the inner layer being clear. These two layers are separated by an air gap. Double glazing, compared to single glazing, cuts heat loss in half due to the insulating air space between the glass layers. Bronze and gray tinted glass products are similar in energy performance. The primary purpose of the bronze or gray tint is to reduce solar heat gain. But, it also reduces visible light transmission compared to clear glass or even other standard tinted glass products such as green and blue tints which offer significantly higher visible light transmission. Tinted glass is useful in controlling glare but solar heat gain and visible light transmission may be reduced relative to the performance of alternate glazing options such as low-E glass with moderate or low solar gain.

The tint has no effect on the U-factor but reduces solar gain which may be a benefit in the summer and a liability in the winter depending on local climate conditions.

Center of Glass Properties

Note: These values are for the center of glass only. They should only be used to compare the effect of different glazing types, not to compare total window products. Frame choice can drastically affect performance. These values represent double glazing with a 1/2" air gap.

Whole Window Properties - Double-Glazed, Tinted Glass
  Metal Frame Metal Frame Non-metal Non-metal
Frame Metal Frame Metal Frame with Thermal Break Non-metal Frame Non-metal Frame, Thermally Improved
U-Factor 0.71-0.99 0.56-0.70 0.41-0.55 n/a
SHGC 0.41-0.60 0.41-0.60 0.41-0.60 n/a
VT 0.51-0.60 0.41-0.50 ≤0.40 n/a
Note: The thermal performance properties of specific glazings and frames can vary depending on product design and materials.
The results presented here are averages. Consult specific manufacturers for NFRC rated U-factors and SHGCs for products of interest.