The Two Numbers on the Label
- U-factor measures how much heat escapes. Lower is better. In a Rapid City winter, this is the number that matters most.
- SHGC (solar heat gain coefficient) measures how much of the sun’s heat passes through. In the north, some solar gain in winter is welcome.
Both are printed on the NFRC label on every rated window. Ask installers to give you these numbers for the exact product they are quoting.
Northern Zone Criteria (Version 7)
| Path | U-factor | SHGC |
|---|---|---|
| Prescriptive | ≤ 0.22 | ≥ 0.17 |
| Equivalent performance | 0.23–0.24 | ≥ 0.35 |
| Equivalent performance | 0.25–0.26 | ≥ 0.40 |
From the ENERGY STAR Version 7 specification. The trade-off rows let a window with slightly more heat loss qualify if it lets in more free solar heat. Check ENERGY STAR for any updates.
Double vs. Triple Pane
Hitting 0.22 often takes triple-pane glass or a double-pane unit with advanced coatings and gas fill. Triple pane is heavier and costs more ($450–$3,000 per window per HomeGuide), but it also makes the inside glass warmer, which means less condensation and less of a cold-draft feeling near the window. Compare actual U-factors rather than pane counts.
Orientation in Rapid City
South-facing windows can collect useful winter sun, so a higher SHGC there can help. West-facing glass can overheat a room on summer afternoons. Some homeowners choose different glass for different sides of the house. Ask whether your installer can do that.
Installation Matters as Much as Glass
A great window leaks if it’s poorly sealed. Ask how the installer insulates and seals the gap between the window and the rough opening, and how they flash the exterior to keep out wind-driven rain and snowmelt.
Condensation Isn’t Always the Window
Water on the inside of the glass on a cold morning can come from high indoor humidity, not failed windows. Fog between the panes, on the other hand, means a seal has failed.
Request a Free Window Estimate
A couple of quick questions, then an independent window company that works in your town will contact you to measure.
Please note: Rapid City Window Replacement refers homeowners to independent window installers. We are not a contractor.