Get a free window quote

Buyer's shortlist

Denver Window Editorial Team

Published 2026-10-13
Updated 2026-10-13

Best Replacement Window Brands in 2026: the buyer's shortlist for Denver homes

Andersen leads this shortlist for Denver homes. The 100 Series glass sheet, dated October 2025, publishes sample total-unit U-factors as low as 0.15, and the company has made windows since 1903. Rankings use frame material, ENERGY STAR Northern-zone fit, warranty length, product lines, and published U-factor. If you are shopping the best replacement windows for a Front Range winter, ask for the Northern-zone mark on the NFRC label, then read the warranty in the manufacturer's words.

Key Takeaways

  • Andersen is first because its 100 Series sheet prints a sample U-factor of 0.15 and the lineup names Fibrex composite, vinyl-clad wood, and wood interiors. A lower U-factor means less heat loss through the whole unit, which is the number that matters in a cold climate. An installed Denver price is not published on Andersen's pages.
  • ENERGY STAR Version 7.0, effective 23 October 2023, sets the Northern prescriptive bar at a U-factor of 0.22 or lower and an SHGC of 0.17 or higher. An equivalent path allows U-factor 0.23 with SHGC at least 0.35, up through U-factor 0.26 with SHGC at least 0.40. Ask which path the exact unit uses, because one glass package can miss the Northern mark even when the brand sells other packages that meet it.
  • Pella's Impervia double-hung manual marks NaturalSun+ argon glass at U-factor 0.25 and SHGC 0.48 as Northern, and a high-altitude NaturalSun+ air unit at U-factor 0.26 and SHGC 0.48 as Northern as well. That high-altitude row is the one to request at Denver's elevation. The same manual marks some high-altitude SunDefense+ packages for South-Central and Southern only.
  • Andersen prints 20 years on glass and 10 years on non-glass parts, and the warranty can transfer. Pella's Duracast lifetime on rectangular Impervia frames is for the original owner of an owner-occupied single-family home and does not transfer. Milgard's current warranty index calls the full lifetime warranty optional, effective 1 January 2026, on Tuscany, Trinsic, and C700.
  • None of the five brands publish an installed Denver price or a review count on the pages cited here. Use the replacement cost guide for a budgeting range by material, then make each bidder name the series, the NFRC U-factor, and the warranty section that applies to your house.

A basement bedroom is a new opening, not a pocket replacement. The net clear sizes an inspector measures are on the installation and egress page.

What a replacement window actually is (and what it is not)

A replacement window is a new manufactured unit set into an opening that already exists. An insert, also called a pocket replacement, keeps the existing frame and sets the new unit inside it. A full-frame replacement removes the old frame down to the rough opening. Insert work leaves the exterior alone and gives up a strip of glass. Full-frame work keeps the original glass size and is the route when the sill is rotten. Neither job is a new-construction window with a nailing fin. The installation page covers new openings, including basement egress.

The number that describes the unit is the NFRC total-unit rating, not a center-of-glass figure. U-factor is heat loss through the frame, spacer, and glass together. Lower means less heat loss. SHGC is the fraction of solar heat that comes through. ENERGY STAR Version 7.0, effective 23 October 2023, uses those two numbers to mark a climate zone. The Northern zone is the cold-climate set: a U-factor of 0.22 or lower and an SHGC of 0.17 or higher, or an equivalent pair up to a U-factor of 0.26 with an SHGC of 0.40 or higher. The Denver area sits in a cold climate, so request the Northern column and confirm the county in the ENERGY STAR climate zone finder.

A brand builds the unit. It is not the crew that sets it, and it is not a price. The series on the bid has to match the series whose warranty and U-factor you read. High altitude changes the build. Andersen's double-hung NFRC sheet says ratings can change when the glass is made for high altitude. Pella prints separate high-altitude rows, and some of those rows lose the Northern mark. Ask for the high-altitude NFRC line on every Denver quote.

Take the shortlist into the bid. Name the series and the Northern-zone glass package before anyone sits down with a single number.

Get a free window quote

How We Ranked These Replacement Window Brands

Five published facts set the order. Frame materials are the materials the manufacturer names for current lines: vinyl, fiberglass or composite, and wood or a wood interior. ENERGY STAR climate zone fit means a current manufacturer document marks a specific glass package for the Northern zone under Version 7.0, or the printed U-factor and SHGC meet that specification. The criteria come from the ENERGY STAR Version 7.0 specification, effective 23 October 2023. Warranty length is the term printed for glass and for the frame, plus whether that term transfers. Product lines are the named series on the manufacturer site. Published U-factor range is the low and high total-unit U-factor on the document we cite, for the glass packages printed there.

Andersen is first: a sample U-factor of 0.15, Fibrex plus vinyl-clad wood plus wood interiors, and a transferable 20-year glass term. Pella is second: an Impervia high-altitude unit still marked Northern, plus vinyl, fiberglass, and wood lines. Milgard is third: a Tuscany picture window at U-factor 0.22 marked for every U.S. zone on that chart row, in vinyl, with a fiberglass line beside it. Marvin is fourth: a stainable pine interior and a fully transferable 20/10 warranty, with no numeric U-factor on the pages cited. Simonton is fifth: vinyl and a residential lifetime warranty on the frame, with U-factor and Northern fit not published. Installed price, review scores, and review counts stayed out of the rank because they are not published on these sources.

The Best Replacement Window Brands in 2026

These five brands are the shortlist. Each write-up uses the manufacturer's own pages for year, materials, warranty terms, and U-factor. Where a figure is missing, the cell says not published. The order follows the five criteria above.

1. Andersen, best for cold-climate glass across more than one frame

Andersen has made windows since 1903. Named lines are the 100 Series in Fibrex composite, the 200 Series and 400 Series in wood with vinyl cladding, and the A-Series and E-Series, which the support FAQ lists among lines with wood interiors. The 100 Series page says Fibrex is twice as strong as vinyl and similar in price to vinyl. Dealers and The Home Depot sell the products in all 50 states. Renewal by Andersen, the replacement subsidiary, opened its first store in 1995 and now covers more than 100 U.S. markets. An installed price and a review count are not published.

The support FAQ states the non-coastal warranty as 20 years on standard glass and 10 years on non-glass components, transferable to the next homeowner. A separate 2-year installation warranty applies only when an Andersen Certified Contractor does the work. The October 2025 glass sheet publishes sample total-unit U-factors for casement, awning, and picture windows, and it says the configured unit has to be confirmed in the order tool. Triple-pane Low-E SmartSun is 0.15 with SHGC 0.28 on the picture column, which meets the Northern prescriptive pair: U-factor 0.22 or lower and SHGC 0.17 or higher. Casement and awning on that row are 0.18. Dual-pane Low-E on the same sheet is 0.28. A double-hung NFRC sheet, accurate as of October 2025, lists high-performance dual-pane glass without grilles at U-factor 0.30, SHGC 0.31, and visible transmittance 0.53. That 0.30 does not meet the Northern cap of 0.26. The sheet says ratings can change with high-altitude glass.

Best suited for: Andersen fits a Denver house that needs a low published sample U-factor and more than one frame, including a wood interior. Confirm the NFRC label, including high-altitude glass, before you treat a 0.15 sample as the unit you will receive.

Source: Andersen support FAQ, 100 Series, company story, 100 Series glass sheet (10/25), 100 Series double-hung NFRC sheet.

Public video on ENERGY STAR windows and the NFRC label: https://www.youtube.com/watch?v=oxzLleuLun0.

2. Pella, best for fiberglass with a high-altitude Northern row

Pella's history page dates the company to 1925, Impervia fiberglass to 2003, the first aluminum-clad line to 1971, Architect Series Reserve wood windows to 2017, and a hidden screen on the vinyl 250 Series to 2022. Encompass by Pella is vinyl. The about page says the company holds over 150 product and design patents. An installed price is not published. A review count is not published.

The Impervia warranty covers rectangular Duracast frames for as long as the original owner owns and occupies a single-family home, and that lifetime does not transfer. After a sale or a move-out it is replaced by a 10-year transferable warranty on materials and workmanship. Glass seal coverage is 20 years and can transfer. Labor is included only within two years of the sale. Nonrectangular shapes are on a 10-year material warranty, not the Duracast lifetime.

The double-hung manual, updated to ENERGY STAR version 7 (2023), lists NaturalSun+ argon unit PEL-N-126-01427-00001 at U-factor 0.25, SHGC 0.48, visible light 0.58, marked N. A foam-filled NaturalSun+ row, PEL-N-126-01539-00001, is U-factor 0.24, SHGC 0.48, also marked N. High-altitude NaturalSun+ with foam, PEL-N-126-01537-00001, is U-factor 0.26, SHGC 0.48, marked N, the equivalent path for a U-factor of 0.26. High-altitude SunDefense+ without foam, PEL-N-126-01397-00001, is U-factor 0.26, SHGC 0.21, marked SC and S only. The Impervia spec sheet says optional high-altitude low-e glass is available with or without argon on select products.

Best suited for: Pella fits a Denver opening where you want fiberglass and a glass row the manufacturer already marks for high altitude and the Northern zone. Specify NaturalSun+ or another package marked N, and do not accept a SunDefense+ high-altitude package that the same manual marks for warmer zones.

Source: Pella history, Pella about, Impervia warranty, Impervia double-hung manual, Impervia spec sheet.

3. Milgard, best for vinyl with a published Northern U-factor

Milgard's Trinsic brochure says the company has designed windows since 1962. The warranty index names V400 Tuscany (vinyl), V300 Trinsic (fiberglass), and C700, plus V250 Style Line, C650 Ultra, V450 HomeMaker, A250 thermally improved aluminum, and V150 vinyl. Effective 1 January 2026, that index lists an optional full lifetime warranty for Tuscany, Trinsic, and C700. The full lifetime PDF for products after 1 April 2021 limits the longest term to an owner who owns and lives in the dwelling. A later owner falls to a 10-year parts warranty, with skilled labor inside the service territory. Frame-finish coverage in that PDF is 10 years. Screens and weatherstripping are one year. An installed price is not published. A review count is not published.

The V400 Tuscany thermal chart, revision date 7 March 2024, is the U-factor source. A picture window with 7/8 inch SunCoatMax, a foam spacer, a 4th surface, and argon, no grids, is U-factor 0.22, SHGC 0.21, marked N, NC, SC, and S. That pair meets the Northern prescriptive rule. A double-hung with 3/4 inch Cardinal 180, an Intercept spacer, a 4th surface, and argon, no grids, is U-factor 0.26, SHGC 0.46, marked N. The same block lists sculptured-grid SunCoat air at U-factor 0.35 with no zone marked. The chart says components vary by manufacturing location. A high-altitude glass table is not published on the pages used here.

Best suited for: Milgard fits a vinyl replacement where you can point at a Tuscany row already marked N, and where you will ask whether the optional full lifetime warranty is on your order. Confirm that Denver sits inside the service territory before you count on labor coverage.

Source: Trinsic brochure, Milgard warranty index, Full lifetime warranty PDF, V400 Tuscany thermal chart.

4. Marvin, best for a stainable pine interior

Marvin's Essential catalog says the company has been family-owned since 1912. The portfolio is the Signature collection (Ultimate, Modern, and Coastline), Elevate, and Essential. Essential uses Ultrex fiberglass inside and out. Elevate uses an Ultrex exterior and a pine interior that can be stained, or a factory clear coat, Designer Black, or white. The Elevate page says Ultrex is 8 times stronger than vinyl and has a low thermal expansion rate. Essential's catalog states a fully transferable warranty of 20 years on glass and 10 years on materials and workmanship. The double-hung page says there are options to meet ENERGY STAR throughout the United States, with dual-pane and triple-pane glass, in sizes up to 4 feet wide by 6 feet 6 inches high. An installed price is not published. A review count is not published.

Marvin's energy page describes Low E1 as the Northern package: a low U-factor and high solar heat gain. The catalog says Essential offers Low E1, Low E2, Low E3, and Low E3/ERS glass with argon, and that argon has thermal conductivity 30 percent lower than air. A numeric U-factor for a named package is not printed on those pages, so the table says not published. A high-altitude row is not published either. The frame size is not a net clear opening, so it cannot be checked against the egress page without the bidder's clear-opening figure.

Best suited for: Marvin fits a historic Denver interior that needs a pine sash you can stain, with a fiberglass exterior and a warranty that transfers in full. Get the NFRC label for Low E1 or another Northern package, because the collection pages do not print the U-factor you will be sold.

Source: Essential catalog, Elevate collection, Essential double hung, Marvin energy efficiency.

5. Simonton, best for a vinyl frame warranty when the NFRC label is in the bid

Simonton's Reflections 5500 brochure says the company handcrafted its first products in 1946. That brochure presents the 5500 as a vinyl replacement window. The warranty index posts lifetime limited warranties for the 5500, 5050, Asure, and Inovo collections, with separate PDFs by purchase date. The 5500 chart lists lifetime coverage on vinyl, hardware, and screens for a residential holder, and 10 years for a multi-resident installation. The insulating glass section states 20 years to lifetime, prorated, with a no-charge replacement during the first 20 years. Glass breakage coverage for double-strength glass is 3 years. That section recommends capillary tubes at 7,000 feet or more. This site publishes Denver at 5,280 feet, under that line. An installed price and a review count are not published.

A published U-factor and an ENERGY STAR Northern mark are not on the Simonton pages used here, so both cells say not published. That is why Simonton is fifth: the cold-climate criteria cannot be scored from these documents. Order the NFRC label with the bid and compare it with the Northern pairs, a U-factor of 0.22 or lower with SHGC of 0.17 or higher, or a U-factor of 0.26 with SHGC of 0.40 or higher. If the label misses those pairs, the vinyl warranty does not fix the climate fit.

Best suited for: Simonton fits a straightforward vinyl replacement when the warranty on the vinyl is the feature you are buying and you will not sign until the NFRC label shows a Northern-zone pair. It is a weak fit if you need a published U-factor or a wood interior before you request quotes.

Source: Reflections 5500 brochure, Simonton warranty index, 5500 warranty PDF.

Side-by-Side Comparison

Criteria, one line: frame materials offered, ENERGY STAR Northern-zone fit, published warranty length, product lines available, and published U-factor range.

Published manufacturer figures only. Blank means the cited pages do not print the figure. "Not published" is used in the same way.
Brand Frame materials ENERGY STAR Northern fit Published warranty length Product lines Published U-factor range
Andersen Fibrex composite (100). Wood with vinyl cladding (200, 400). Wood interiors (A-Series, E-Series). 100 Series samples meet Northern pairs: picture triple-pane Low-E SmartSun U-factor 0.15, SHGC 0.28. Double-hung dual-pane example at 0.30 does not. 20 years glass, 10 years non-glass, transferable. Install coverage 2 years only with an Andersen Certified Contractor. 100, 200, 400, A-Series, E-Series. Renewal by Andersen is the replacement subsidiary. 0.15 to 0.29 on the 100 Series casement, awning, and picture sample sheet. Double-hung high-performance dual-pane example 0.30.
Pella Fiberglass (Impervia). Vinyl (Encompass, 250 Series). Wood (Architect Series Reserve). Aluminum-clad since 1971. Impervia double-hung NaturalSun+ marked N, including a high-altitude air unit at U-factor 0.26, SHGC 0.48. Some high-altitude SunDefense+ rows are SC and S only. Duracast lifetime for the original owner-occupier, nontransferable. Glass 20 years, transferable. Other materials 10 years, transferable. Labor 2 years. Impervia, Encompass, 250 Series, Architect Series Reserve. NaturalSun+ 0.24 (foam) and 0.25, both marked N. High-altitude with foam: 0.26, marked N. Non-foam high-altitude NaturalSun+ prints 0.27 with no zone letter on that line. SunDefense+ argon: 0.23 to 0.24, marked NC, SC, S.
Milgard Vinyl (Tuscany V400, V150). Fiberglass (Trinsic V300). Thermally improved aluminum (A250). Tuscany picture window, SunCoatMax foam, 4th surface, argon, no grids: U-factor 0.22, SHGC 0.21, marked N, NC, SC, S. Double-hung Cardinal 180 at 0.26, SHGC 0.46, marked N. Optional full lifetime on Tuscany, Trinsic, and C700, effective 1 January 2026. 2021 warranty text: longest term for the original resident owner. Later owners: 10-year parts. V400 Tuscany, V300 Trinsic, C700, V250 Style Line, C650 Ultra, V450 HomeMaker, A250, V150. 0.22 to 0.35 on the V400 chart rows cited (picture 0.22, double-hung sculptured-grid SunCoat air 0.35).
Marvin Ultrex fiberglass interior and exterior (Essential). Ultrex exterior with pine interior (Elevate). Essential page: options to meet ENERGY STAR through the United States. Low E1 is described as the Northern package. A numeric Northern row is not published. Essential: 20 years glass, 10 years materials and workmanship, fully transferable. Signature (Ultimate, Modern, Coastline), Elevate, Essential. not published
Simonton Vinyl (Reflections 5500). not published Residential: lifetime on vinyl, hardware, and screens. Insulating glass: 20 years to lifetime, prorated, no-charge for the first 20 years. Breakage: 3 years for double-strength glass. Multi-resident: 10 years. 5500, 5050, Asure, Inovo. not published

Which window brand fits your home

Use-case map from the same sources. Hail impact ratings are not published for these brands.
Brand Budget vinyl replacement High-altitude sun and hail exposure Historic homes Basement and egress windows
Andersen 100 Series Fibrex, described as similar in price to vinyl. Not a vinyl frame. Double-hung sheet says high-altitude glass can change the NFRC rating. Hail impact rating: not published. 200 and 400 Series wood with vinyl cladding. A-Series and E-Series have wood interiors. Net clear opening: not published. See the egress sizes.
Pella Encompass vinyl line. High-altitude NaturalSun+ double-hung, U-factor 0.26, SHGC 0.48, marked Northern. Hail impact rating: not published. Architect Series Reserve wood, dated 2017 on the history page. Net clear opening: not published.
Milgard V400 Tuscany vinyl. Northern packages are on the thermal chart. A high-altitude glass note: not published. Hail impact rating: not published. Wood interior: not published. Net clear opening: not published.
Marvin Vinyl line: not published. Essential is Ultrex fiberglass. Low E1 described for Northern. High-altitude row: not published. Hail impact rating: not published. Elevate pine interior, which can be stained. Essential double-hung frame up to 4 ft wide by 6 ft 6 in high. Net clear opening: not published.
Simonton Reflections 5500 vinyl. Northern mark: not published. Warranty recommends capillary tubes at 7,000 feet or more. Hail impact rating: not published. Wood frame: not published. Net clear opening: not published.

What results look like

Example, not a bid. The replacement cost guide publishes Denver metro installed ranges of $575 to $950 for vinyl, $850 to $1,450 for fiberglass, and $1,000 to $1,900 for wood or clad wood. Ten vinyl windows at the published ends is $5,750 to $9,500. The same guide says full-house jobs run about 12 percent off per-window pricing at ten or more openings. Twelve percent off those ends is about $5,060 to $8,360. That arithmetic uses this site's ranges. It is not an Andersen, Pella, Marvin, Milgard, or Simonton price. None of those brands publish an installed Denver price on the pages cited above.

Second example, from the comparison table. Heat loss through a rated unit scales with U-factor when the area and the indoor-outdoor temperature difference stay the same. Andersen's own gloss is that U-factor is heat loss through the total unit in BTU/hr-ft2-°F, and that a lower value means less heat lost. Milgard's cited picture-window package at 0.22 divided by Andersen's cited double-hung dual-pane example at 0.30 is 0.73. That is about 27 percent less heat flow through the lower-U unit under those same conditions. The two ratings are different operators, picture versus double-hung, so this is a reading of the published numbers, not a prediction for one opening in one house.

Common questions

What is a replacement window?

A replacement window is a new unit set into an opening that already exists. An insert keeps the old frame, and a full-frame job removes that frame down to the rough opening. A new hole in the wall, including most basement egress windows, is installation, not replacement.

How does ENERGY STAR define a cold-climate window?

Version 7.0, effective 23 October 2023, sets Northern prescriptive criteria at a U-factor of 0.22 or lower and an SHGC of 0.17 or higher. Equivalent pairs run from U-factor 0.23 with SHGC at least 0.35 up to U-factor 0.26 with SHGC at least 0.40. The Denver area is a cold climate, so ask for a unit marked for that Northern zone and confirm the county in the ENERGY STAR climate zone finder.

What U-factor should I ask a bidder to print on the quote?

Ask for the NFRC total-unit U-factor and SHGC, not a center-of-glass number. On the pages cited here, published samples run from 0.15 on an Andersen 100 Series triple-pane picture window to 0.35 on a Milgard Tuscany double-hung with no Northern mark. The label has to match the opening, including high-altitude glass.

How does high altitude change the glass I should order?

Andersen's double-hung NFRC sheet says ratings can change when the glass is built for high altitude. Pella prints separate high-altitude rows: one NaturalSun+ air unit at U-factor 0.26 and SHGC 0.48 is still marked Northern, while a SunDefense+ high-altitude unit at U-factor 0.26 and SHGC 0.21 is marked only for South-Central and Southern. Order the high-altitude line and read the zone letters on that row.

What is the difference between a lifetime warranty and a 20-year glass warranty?

They cover different parts, and lifetime usually means the original owner only. Pella's Duracast lifetime on rectangular Impervia frames does not transfer, while Andersen's non-coastal warranty is 20 years on glass and 10 years on non-glass parts and can transfer. Milgard's full lifetime warranty is listed as optional as of 1 January 2026.

How do I compare brands when the price is not on the brand site?

None of the five manufacturers publish an installed Denver price on the pages cited here. Start with this site's material ranges, $575 to $950 for vinyl, $850 to $1,450 for fiberglass, and $1,000 to $1,900 for wood or clad wood, and treat them as budgeting bands. Then require every bidder to price the same series, the same glass package, and the same insert or full-frame choice.

What should I measure for a basement egress window?

The installation page cites the International Residential Code figures used by Colorado jurisdictions: at least 5.7 square feet of net clear opening, or 5.0 square feet at grade, at least 24 inches clear height, at least 20 inches clear width, and a sill no more than 44 inches above the finished floor. Marvin publishes an Essential double-hung frame size up to 4 feet by 6 feet 6 inches, which is not the same as net clear opening. Ask the bidder for the net clear opening of the unit you will actually get.

Sources

Get a free window quote

Take one series and one Northern-zone glass package from this shortlist into every bid. The quote checklist is the list of lines to require, including U-factor, insert or full-frame, and permit responsibility. Use that checklist on the how to get window quotes page. Ask for the NFRC label on the exact unit, with high-altitude glass called out. Match the label to the comparison table before you discuss a discount. Collect more than one bid on the same series list.

Get a free window quote