Step 1: read the label
Every NFRC-certified window carries a label with these ratings (NFRC):
| Rating | What it measures | Better is |
|---|---|---|
| U-Factor | How well the window keeps heat from escaping | Lower |
| Solar Heat Gain Coefficient (SHGC) | How much solar heat it lets in | Lower in hot climates; higher can help in cold winters |
| Visible Transmittance | How much daylight it lets in | Higher |
| Air Leakage (optional) | How much air comes through | Lower |
| Condensation Resistance (optional) | How well it resists condensation | Higher |
Ask every company for the NFRC ratings of the exact window it is quoting, in writing. A company that cannot give them is quoting a window you cannot compare.
Step 2: match the label to your zone
ENERGY STAR certified windows are made by an ENERGY STAR partner and "independently tested, certified, and verified by the National Fenestration Rating Council" (ENERGY STAR). The limits, from its criteria table:
| ENERGY STAR zone | U-factor | SHGC | Examples among our cities |
|---|---|---|---|
| Northern | 0.22 or lower (or 0.23–0.24 with SHGC 0.35+, 0.25–0.26 with SHGC 0.40+) | 0.17 or higher | Minneapolis, Saint Paul, Burlington VT, Somerville |
| North-Central | 0.25 or lower | 0.40 or lower | Use the ENERGY STAR map |
| South-Central | 0.28 or lower | 0.23 or lower | Use the ENERGY STAR map |
| Southern | 0.32 or lower | 0.23 or lower | Miami, Cape Coral |
All zones: air leakage 0.3 cfm per square foot or less. Zone lines follow counties, so check yours on the ENERGY STAR map rather than guessing from the state.
The tax-credit question is settled for now: the IRS energy efficient home improvement credit, which allowed up to $600 for qualifying windows and skylights, applies to improvements made through 31 December 2025 (IRS, page reviewed April 2026).
Step 3: check the company on the permit record
What window permits look like in our cities. "Reached final" is the share of permits a year or more old the city closed out.
| City | Window permits | Firms | Usual filed value | Middle half of firms | Reached final | Active license match |
|---|---|---|---|---|---|---|
| Minneapolis | 5,528 | 478 | $8,000 | $4,500 to $11,500 | 81.8% | 78.7% |
| Saint Paul | 3,977 | 503 | $7,220 | $4,000 to $10,000 | 63.4% | 75.9% |
| Miami | 4,921 | 1,096 | $14,246 | $8,000 to $19,106 | 98.5% | 93.0% |
| Cape Coral | 4,787 | 433 | $13,452 | $9,600 to $17,921 | 96.8% | 99.5% |
| San Francisco | 4,050 | 1,358 | $24,000 | $17,000 to $80,000 | 85.9% | 93.2% |
| Sacramento County | 1,589 | 176 | $13,110 | $7,896 to $20,000 | 91.7% | 84.7% |
| Cleveland | 2,938 | 236 | $5,900 | $4,775 to $14,782 | 75.2% | not matched |
| Somerville | 547 | 202 | $16,700 | $8,715 to $26,980 | 52.5% | not matched |
Three things to look for on the firm's page:
- A run of window permits in your city. A company with dozens of finished window permits has passed this inspector's checks before. One with a single permit may be new, or may usually skip the permit.
- Its finished share against the city's. In Saint Paul, 63.4% of window permits reached a final, against 81.8% across the river in Minneapolis. A firm well under its city's figure leaves permits open.
- Its usual job value against your quote. If the middle half of Minneapolis firms file $4,500 to $11,500 and your quote is three times the top of that for a similar number of windows, ask why.
Compare every Minneapolis window company by permit record →
Questions that separate window companies
| Ask | A good answer |
|---|---|
| What are the NFRC U-factor and SHGC of the window you are quoting? | Numbers, from the label, that meet your zone's limits |
| Who installs it: your crew or a subcontractor? | A name you can look up; the permit should be in the company's name |
| Who pulls the permit? | "We do"; see do I need a permit for window replacement |
| In Florida: what is the product approval? | A Miami-Dade NOA or Florida product approval number; see hiring a window installer in Miami |
| What is the installation warranty, separate from the manufacturer's? | Years and what it covers, in writing |
What this does not tell you
The permit file does not record which window was installed, so we cannot rank companies by product quality or energy performance; the NFRC label is the only source for that. Usual values mix full-house and single-window jobs. Minnesota, Florida and California window firms are matched to state licenses; we have not matched Cleveland or Somerville installers, so check them on the city or state register yourself. Prices for the window itself are in window replacement cost.
How we know this
Label ratings are from the NFRC home page; ENERGY STAR criteria are from its criteria table (October 2023 version) and zone map, and the tax credit dates from the IRS credit page, all read 23 October 2026. Window permits are those each city files under a window or window-and-door replacement work type in its window (three years ending September 2026; Cape Coral from January 2025). Usual filed value is the median declared value; the firm range is the 25th to 75th percentile of firms' medians (firms with 3 or more priced permits); the license match is the share of firms whose name matched an active state license on our snapshot date.
Numbers come from City of Minneapolis construction permits (CCS); City of Miami building permits (since 2014); City of Cape Coral building permits (the city's open permit table starts January 2025); City of Saint Paul building and trade permits (the City's old approved-permits file up to June 2025, and the City's PAULIE permit system since September 2025), with the contractor named on each permit; City of Cleveland building permits; San Francisco DBI building permits on one- and two-family homes, with the contractor from the city's permit contacts file, data through October 19, 2026. Nobody paid to be on this page and nobody can.
Questions
- How do I choose a window company?
Choose the window first, on its NFRC label against the ENERGY STAR limits for your climate zone, then choose the installer on its record: license status, how many window permits it has pulled in your city, and how many reached a final. In Minneapolis, 478 firms filed 5,528 window permits in three years.
- What should I look for on a window label?
The NFRC label gives U-factor (lower keeps heat in), Solar Heat Gain Coefficient (lower blocks solar heat), Visible Transmittance (higher lets in more daylight), and, where rated, air leakage and condensation resistance (NFRC). Compare windows on those numbers, not on brand names.
- What U-factor should a window have?
For ENERGY STAR: 0.22 or lower in the Northern zone (or 0.23 to 0.26 with a higher solar gain), 0.25 or lower in North-Central, 0.28 in South-Central and 0.32 in the Southern zone, with SHGC limits of 0.40 or lower in North-Central and 0.23 or lower in the two southern zones, and air leakage of 0.3 cfm per square foot or less (ENERGY STAR criteria table).
- Is there a tax credit for new windows in 2026?
Not for windows installed in 2026. The IRS says the energy efficient home improvement credit, which allowed up to $600 a year for windows and skylights meeting ENERGY STAR Most Efficient, covers improvements made through 31 December 2025.
- How much does a window company charge?
The usual filed value of a window replacement permit runs from $5,900 in Cleveland to $24,000 in San Francisco, and $14,246 in Miami, where impact windows are the norm. Our window replacement cost guide has 16 cities.
Build your own list
Every firm with that kind of permit on record. Pick what you value. The list moves.
Related guides
- Window replacement cost in 2026: what window permits were filed at in 16 cities
- Hiring a roofer: 5 red flags and 10 questions, checked against roofing permits in 28 cities
- How to check contractor references: ask for addresses, check the permits, and the 8 questions to ask
- Contractor didn't finish the job: what to do, and what the permit file shows
- Hiring a window installer in Miami: the license, the NOA, the permit, and what 4,900 window permits show
For one city
- National Fenestration Rating Council (What does the NFRC label tell you?) (accessed 2026-10-23)
- What makes it ENERGY STAR? Residential Windows, Doors and Skylights — ENERGY STAR (accessed 2026-10-23)
- ENERGY STAR Certification Criteria for Residential Windows (table, Oct 2023) (accessed 2026-10-23)
- ENERGY STAR climate zone map for windows (accessed 2026-10-23)
- Energy Efficient Home Improvement Credit — IRS (last reviewed 28 April 2026) (accessed 2026-10-23)