Yes — many replacement windows do qualify for the federal energy tax credit in 2026, but only if they hit a specific performance threshold. For Danbury homeowners, the short answer is: install ENERGY STAR–certified windows that meet the Northern climate zone criteria (per the IRS Energy Efficient Home Improvement Credit rules), and you can claim 30% of the product cost, up to $600 per year on your federal return. The credit applies to the window itself, not installation labor, and it does not roll over — unused amounts do not carry forward to the next tax year.

Here’s a practical guide to what qualifies, what the specs mean, and how to make sure your Danbury project captures the full credit.

What Is the Federal Energy Tax Credit for Windows?

The Energy Efficient Home Improvement Credit (IRS Section 25C), expanded under the Inflation Reduction Act, lets homeowners claim 30% of the cost of qualifying energy-efficient improvements each year through 2032, per the IRS. For windows and skylights, the annual cap is $600 — a per-taxpayer, per-year limit, not a lifetime limit. You can claim it in multiple tax years for different projects.

The credit applies to the cost of the window unit itself (frame, glazing, hardware). Installation labor is not included in the calculation.

Important: Tax credits reduce what you owe the IRS dollar-for-dollar. If your total federal income tax liability for the year is less than the credit amount, you only capture what you owe — the credit is non-refundable. Consult a tax professional for your specific situation; this post is educational, not tax advice.

The Performance Threshold: What Does “Qualifying” Actually Mean?

To qualify for the 25C credit, a window must be ENERGY STAR–certified and meet the criteria for the climate zone your home is in.

Connecticut and New York fall in the Northern climate zone under ENERGY STAR. Per the ENERGY STAR Version 7.0 Final Specification (effective October 23, 2023):

Per the National Fenestration Rating Council (NFRC), the U-factor measures how much heat the window loses — the lower the number, the better the insulation. SHGC (Solar Heat Gain Coefficient) measures how much solar heat passes through; the Northern zone minimum of 0.17 is intentionally permissive, because in CT and NY you want some solar gain in winter.

A window labeled ENERGY STAR does not automatically qualify for the tax credit if it is certified for a different climate zone. Verify that the NFRC label on the window itself shows U ≤ 0.22 and the product is ENERGY STAR–certified for the Northern zone.

Why Danbury Homeowners Have Extra Incentive to Act

Danbury’s housing stock skews toward the 1950s–1970s — ranch homes, split-levels, and raised ranches built during the postwar suburban expansion inland from the coast. Many of those homes still carry their original single-pane aluminum or steel-frame windows, which are significantly less efficient than today’s qualifying products.

Unlike coastal Fairfield County towns such as Greenwich or Darien, Danbury sits inland. That location produces wider seasonal temperature swings: hotter summer afternoons and colder overnight lows in winter than the Sound-moderated coast. Old windows feel the difference more acutely — more drafts in winter, more solar heat gain on west- and south-facing walls in July and August. Replacing them now, while the 30% credit applies, means energy savings start immediately heading into fall and carry through winter.

What Does the Credit Actually Cover in 2026?

The $600 cap is per year, not per project. If you replace 10 windows at $400 each ($4,000 product cost), 30% of $4,000 = $1,200 — but the credit caps at $600. You can potentially spread the project across two tax years to capture more of the credit, though that requires two separate installations.

How to Confirm a Window Qualifies Before You Buy

1. Look for the ENERGY STAR label — specifically the Northern zone certification. The manufacturer’s spec sheet and the NFRC label on the unit will show U-factor and SHGC.
2. Verify U ≤ 0.22 — this is the binding threshold for the Northern zone per ENERGY STAR v7.0. A product at U-0.25 may still be ENERGY STAR–certified for a different zone (North-Central or South), but it will not qualify for the 25C credit in Connecticut.
3. Get the manufacturer’s certification statement — IRS guidance requires you to keep a written certification from the manufacturer stating the product qualifies. Most manufacturers post these on their websites for qualifying products.
4. File IRS Form 5695 — the credit is claimed on this form when you file your federal return.

What Andersen Windows Qualify?

Gunner installs Andersen windows, and Andersen is Gunner’s recommended window line. Andersen’s 400 Series (wood interior / Perma-Shield exterior) and A-Series (Andersen’s premium Architectural Collection, with wood interior and fiberglass/composite exterior) both include configurations that achieve U-factors at or below 0.22 and carry Northern-zone ENERGY STAR certification — but not all configurations do. The qualifying U-factor depends on the specific product, glass package (double- or triple-pane), and low-E coating option you select.

The practical rule: ask your installer to specify a product with a Northern-zone ENERGY STAR label. Gunner is an Andersen Certified Elite contractor and can confirm which specific configurations meet the 25C threshold for your project before you sign anything.

Connecticut Building Permits for Window Replacement

Replacing windows in Connecticut generally requires a building permit. Requirements vary by municipality — confirm with your local building department before starting work. Gunner handles the permit on every project, so that step is covered.

Frequently Asked Questions

How much is the federal tax credit for replacement windows in 2026? The Energy Efficient Home Improvement Credit (IRS Section 25C) covers 30% of qualifying window product costs, capped at $600 per year for windows and skylights combined. It is non-refundable and does not carry over to future years.

What U-factor is required in Connecticut? Connecticut is in the ENERGY STAR Northern climate zone. Per ENERGY STAR v7.0, windows must have a U-factor ≤ 0.22 and SHGC ≥ 0.17 for Northern-zone certification — the threshold that qualifies for the 25C credit.

Does the credit cover installation labor? No. The IRS 25C credit applies to the window product cost only. Labor is excluded.

Can I split a project across two tax years? The $600 cap resets annually, so two separate installations in two separate tax years can each generate up to $600. Consult a tax professional for your situation.

Do Andersen windows qualify? Many 400 Series and A-Series configurations meet the U ≤ 0.22 threshold — but not all. Confirm the NFRC label on the specific glass package before purchasing.

How do I claim it? File IRS Form 5695 with your federal return for the year the windows were installed. Keep the manufacturer’s certification statement and your itemized receipts.

Ready to get an estimate on ENERGY STAR–qualifying windows for your Danbury home? Get a free, no-obligation quote at GunnerRoofing.com.