Energy Efficiency Ratings
There are 3 common criteria used to measure a windows energy efficiency: Solar Heat Gain Coefficient (SHGC), Visible Transmittance (VT), and U-factor. These terms are defined below and will help you evaluate windows for your home.
The National Fenestration Rating Council (NFRC) administers a certification process that some manufacturer's use to certify their test results. The ratings in the chart below have all been certified by the NFRC.
BTU - An abbreviation for British Thermal Unit - the heat required to increase the temperature of one pound of water one degree Fahrenheit.
Solar Heat Gain Coefficient (SHGC) - A measure of the solar radiation admitted through a window or skylight. It is expressed as a number between 0 and 1. the SHGC can be expressed in terms of the glass alone or the entire window assembly (our numbers are entire window values). The lower the number, the less solar heat that it transmits, and the greater it's shading ability. This is the standard indicator of a window's shading ability.
Visible Transmittance (VT) - A measure of the amount of light admitted through a window or door. It is expressed as a number between 0 and 1 (1 being full transmission). This has little direct impact on heating or cooling loads within a building, but is an important factor in determining visibility as well as controlling glare and fading of interior furnishings.
U-factor - A measure of the rate of non-solar heat loss or gain through a door or window. The U-factor may be expressed for the glass alone or for the entire window (all of our published numbers are entire window values). The lower the U-factor, the greater the unit's resistance to heat flow and the better its insulating value. The U-factor is measured in BTU's per hour per square foot per degree fahrenheit.
R-value - A measure of the resistance of a glazing material or window or door assembly to heat flow. A high R-value window has a greater resistance to heat flow and a higher insulating value than one with a low R-value. It is the inverse of the U-factor (1/U-factor) and is measured in degrees per hour per square foot per BTU.
Glass options in blue type are ENERGY STAR qualified
| Product | Glass | Gap Fill | U-Factor | R-Factor | SHGC | VT | |
| 270 / 570 SH | Clear | Air - Intercept | 0.49 | 2.04 | 0.56 | 0.58 | |
| Low-e | Air - Intercept | 0.36 | 2.78 | 0.30 | 0.49 |  | |
| HPG | Argon - Superspacer | 0.31 | 3.23 | 0.30 | 0.49 | ||
| 270 / 570 PW | Clear | Air - Intercept | 0.51 | 1.96 | 0.62 | 0.64 | |
| Low-e | Air - Intercept | 0.36 | 2.78 | 0.31 | 0.49 | | |
| HPG | Argon - Superspacer | 0.31 | 3.23 | 0.31 | 0.49 | ||
TrustGard DH DuraTrust DH 730 DH | Clear | Air - Intercept | 0.48 | 2.08 | 0.52 | 0.54 | |
| Low-e | Air - Intercept | 0.35 | 2.86 | 0.28 | 0.46 |  | |
| HPG | Argon - Superspacer | 0.31 | 3.23 | 0.28 | 0.46 | ||
TrustGard Slider DuraTrust Slider 730 Slider | Clear | Air - Intercept | 0.47 | 2.13 | 0.54 | 0.56 | |
| Low-e | Air - Intercept | 0.34 | 2.94 | 0.29 | 0.47 | | |
| HPG | Argon - Superspacer | 0.30 | 3.33 | 0.28 | 0.47 | ||
TrustGard PW DuraTrust PW | Clear | Air - Intercept | 0.46 | 2.17 | 0.56 | 0.59 | |
| Low-e | Air - Intercept | 0.32 | 3.13 | 0.30 | 0.50 | | |
| HPG | Argon - Superspacer | 0.27 | 3.70 | 0.30 | 0.50 | ||
| 730 PW | Clear | Air - Intercept | 0.47 | 2.13 | 0.60 | 0.65 | |
| Low-e | Air - Intercept | 0.33 | 3.03 | 0.33 | 0.55 | | |
| HPG | Argon - Superspacer | 0.27 | 3.70 | 0.33 | 0.55 |
