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HomeEfficiency guide

Energy-Efficient Windows in Wisconsin

Wisconsin is a heating-dominated climate. A window here spends most of the year holding heat in, not keeping it out, and that changes which numbers on the label matter.

On this page
  1. The two numbers on the label
  2. Why we do not print threshold numbers
  3. What the rebate requires
  4. What matters as much as the glass
  5. Does new glazing fix a cold room?
  6. Next
  7. Sources

This page explains the two numbers you will be shown, and what the rebate programme requires. It does not print threshold values, and we explain why below.

The two numbers on the label

Every certified window carries an NFRC label. Two figures on it do most of the work.

U-factor measures how fast heat passes through the whole window assembly: frame, spacer, glass and all. Lower is better. A lower U-factor means less heat escaping on a January night. Because it is measured for the whole assembly, a good glass package in a poor frame does not rate as well as the glass alone would suggest.

SHGC, or Solar Heat Gain Coefficient, measures how much of the sun's heat the window lets through, as a fraction between 0 and 1. Lower means less solar heat admitted. In a hot climate you want it low. In Wisconsin it is a trade-off: solar gain on a south-facing window is free winter heat, but the same window can overheat a room in July.

There is a third figure worth asking about, visible transmittance, which describes how much daylight comes through. Low-E coatings that cut solar gain also cut light.

Why we do not print threshold numbers

ENERGY STAR Version 7.0 sets specific U-factor and SHGC requirements for the Northern climate zone, which is the zone Wisconsin sits in. We have not been able to read the EPA specification table directly, and we will not publish a threshold we have not verified at source. Manufacturer summaries circulate widely and they do not all agree, particularly about the equivalent-energy paths that allow a slightly higher U-factor in exchange for a higher SHGC.

So: ask your contractor for the NFRC label figures for the exact unit being quoted, and check them against the current ENERGY STAR specification on energystar.gov yourself. Do not accept "it's ENERGY STAR rated" as an answer without the label.

One thing worth knowing: "ENERGY STAR Most Efficient" is a separate, stricter recognition tier, not the same thing as meeting the certification. If a salesperson uses the phrase, ask which one they mean.

What the rebate requires

The Focus on Energy windows rebate requires replacing existing single-pane or clear double-pane windows (that is, double-pane with no low-E coating) with models that are ENERGY STAR Version 7 Northern Climate Certified [W2]. That is the standard named in the programme terms, and it is the one to hold a contractor to if a rebate is part of your plan.

The rebate also requires:

  • A participating Trade Ally contractor, who submits the reservation [W2].
  • A rebate reservation approved before purchase and installation [W2].
  • An itemized invoice carrying a CPD number, plus photos of at least 5% of the windows showing the NFRC sticker [W2].
  • Conditioned space only, in an existing single-family home or a dwelling of three or fewer units [W2].
  • At least 51% of the home's heating supplied by a participating electric or natural gas utility. Wood, oil and LP-heated homes are not eligible [W2].

Purchase and installation must fall between June 1, 2026 and December 15, 2026, while funds last [W2]. If you are starting now, ask the contractor whether a reservation approved before purchase and an installation completed by December 15, 2026 is realistic on their schedule. As of November 13, 2026, no 2027 terms had been published. Confirm current terms with Focus on Energy on 800.762.7077, and read our rebate page before you buy anything.

What matters as much as the glass

A high-performing window installed badly performs badly. In a Wisconsin winter the failures people actually notice are usually not glass failures:

  • Air sealing at the perimeter. The gap between the window frame and the rough opening has to be insulated and sealed. Spray foam stuffed in without an air seal is not the same thing.
  • Flashing and drainage. Water that gets behind the trim rots the sill, and the damage shows up years later.
  • Spacer type. The spacer around the edge of the glass unit is where condensation appears first. Warm-edge spacers perform better than older metal ones.
  • Frame material. Frames conduct heat at very different rates. See window materials.
  • Operable versus fixed. A fixed picture window has no weatherstripping to wear out. Operable units do, and hardware adjustment matters over time.

Does new glazing fix a cold room?

Sometimes, partly. If you can feel air moving at the window, new units and proper air sealing will make a real difference. If the glass is intact and the draught is coming from the rim joist, the attic hatch or an uninsulated wall, new windows will not fix it, and they are among the most expensive ways to try. A whole-home energy assessment first is usually the cheaper order of operations.

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Sources

Note for the reader: ENERGY STAR Version 7.0 Northern-zone U-factor and SHGC thresholds are deliberately not published on this page. Verify them against the current EPA specification on energystar.gov.

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