This is the differential energy use in kBtu per square foot of glass between the generic base case and a selected product(s). The base case window properties are defined in the table below.
All annual energy performance data are given as energy use per perimeter zone floor area (e.g., kWh/sf-yr or kBtu/sf-yr). The perimeter zone is a 10-foot-wide-office space extending 15 feet from the window with a ceiling height of 9 feet and a total floor-to-floor height of 12 feet.
Total annual electricity use (site energy) includes the following electricity end uses: lighting, cooling, and fans for supply, and returns for ventilation, heating, and cooling.
| Construction Type | Window | SHGC | Tvis | U-value |
| New | Double Clear, Air Filled | 0.70 | 0.79 | 0.47 |
| Replacement | 1/4" Monolithic | 0.82 | 0.86 | 1.03 |
The effect of excessive air infiltration through existing operable windows is added to COMFEN-calculated energy savings for each replacement window comparison base case. Click here to review air infiltration calculation methodology and assumptions.
Annual Energy Savings are based on source energy.