Key numbers
45 verified hail storms with stones of 1.75 inches or larger reached Denver County from 1984 to 2026 in the storm records we keep; the largest measured 4.5 inches (softball size) on July 13, 2011 (NOAA NCEI).
| Hail storms by decade, 1984 to 2026 | 1980s: 1, 1990s: 4, 2000s: 12, 2010s: 17, 2020s: 11 Source: Storm library: Denver metro hail history |
|---|---|
| Largest hail | 4.5 in. (softball), July 13, 2011 Source: NOAA NCEI |
| Costliest hail storm | $2.3 billion insured losses (2017 dollars), May 8, 2017 Source: RMIIA |
| Roughly 10% | Windows account for about 5 quads, roughly 10%, of U.S. building energy use, per Berkeley Lab researchers. Source: Lawrence Berkeley National Laboratory / Building Simulation, 2019 |
| $1.33 | Xcel Energy Colorado began offering a $1.33 per square foot rebate in 2020 for AERC-rated insulated cellular shades on single-family homes. Source: U.S. Department of Energy, 2020 (program start) |
| About 2.15 | Windows in U.S. buildings account for about 2.15 quads of heating and 1.48 quads of cooling energy each year. Source: Lawrence Berkeley National Laboratory, 2006 |
A storm counts when the library lists Denver County among the areas it hit. Each hail size is the storm's largest report, which may have fallen in a neighboring county, and insured losses cover every area the storm hit.
To judge a replacement window’s energy performance, read its NFRC label: U-factor (heat loss, lower is better), solar heat gain coefficient or SHGC (how much sun heat comes through), visible transmittance (daylight), and often air leakage and condensation resistance. For ENERGY STAR Version 7.0, a window in the Northern climate zone needs a U-factor of 0.22 or lower and an SHGC of 0.17 or higher, or an approved equivalent pair. Check which zone your ZIP code falls in before comparing quotes. Integrity Roofing and Painting replaces windows in existing Denver and Colorado Springs homes, most often with Simonton units or another brand you choose, and we quote every window with its whole-unit NFRC numbers.
The five numbers on an NFRC label
| Rating | What it measures | Better is | Why it matters here |
|---|---|---|---|
| U-factor | Heat flow through the whole window | Lower | Cold nights most of the year |
| SHGC | Share of solar heat let in | Depends on orientation | Free winter heat on south walls; summer heat on west walls |
| Visible transmittance | Share of daylight let in | Higher for brighter rooms | Low-SHGC glass can look darker |
| Air leakage | Air through the closed unit | Lower | Drafts and dust on windy days |
| Condensation resistance | Resistance to interior condensation | Higher | Dry indoor air, but frosty glass in cold snaps |
NFRC says it does not sell or endorse products. Its Certified Products Directory lets you look up any certified rating, and its consumer site at efficientwindows.org has a window selection tool by climate.
ENERGY STAR Version 7.0 limits
Version 7.0 took effect October 23, 2023. Its window criteria by zone:
| Zone | U-factor | SHGC |
|---|---|---|
| Northern | 0.22 or lower | 0.17 or higher |
| North-Central | 0.25 or lower | 0.40 or lower |
| South-Central | 0.28 or lower | 0.23 or lower |
| Southern | 0.32 or lower | 0.23 or lower |
The Northern zone also allows equivalent pairs: a U-factor of 0.23 or 0.24 with an SHGC of at least 0.35, or 0.25 or 0.26 with an SHGC of at least 0.40. Windows, sliding doors and skylights must also meet an air leakage limit of 0.3 cfm per square foot. Use ENERGY STAR’s own zone lookup for your address rather than assuming. ENERGY STAR is voluntary; the minimum for permitted work is set by the energy code your building department enforces, which differs between Denver, Aurora, Lakewood, Littleton and the counties. Our Denver building code data page lists the city’s adopted codes.
The altitude catch
Denver sits at 5,280 feet and Colorado Springs above 6,000. Sealed glass units built at low elevation bow outward when they arrive here, stressing the glass and edge seal. Makers handle it with capillary or breather tubes that equalize the pressure. Cardinal Glass, a major glass maker, says it does not argon-fill units with capillary tubes and their U-factor should be based on air fill. Ask the window maker which U-factor applies to units built for your elevation, and make sure the quote uses that number.
Do not overbuy on payback alone
The Pacific Northwest National Laboratory’s side-by-side lab homes study measured real savings from highly insulating triple-pane windows and also found payback alone did not justify them. New windows still improve comfort, cut drafts and reduce condensation. If savings are your only goal, read repair or replace first; storm windows over sound old windows can be a better value.
Sun direction matters
On a Front Range house, south-facing glass with a moderate SHGC collects useful winter sun, while west-facing glass overheats rooms on summer afternoons. Some homeowners choose lower-SHGC glass on west walls. Whatever you pick, compare windows by the same whole-unit NFRC ratings.
Next steps
See Denver window replacement or Colorado Springs window replacement for how we install, and replacement window flashing for the water side of the job.
Get a window quote with real numbers
Integrity Roofing and Painting is veteran-owned and family-run since 1990, an Owens Corning Platinum Preferred roofing contractor with 650+ Google reviews. Call our Denver office at (303) 209-0152 or book a free inspection; we respond the same business day.
Sources: ENERGY STAR Residential Windows, Doors and Skylights Version 7.0, Tables 1 and 4; ENERGY STAR, Version 7.0 specification page; National Fenestration Rating Council; NFRC, efficientwindows.org; Cardinal Glass, Capillary Tubes; PNNL, Highly Insulating Windows in the PNNL Lab Homes (PNNL-21678).
