20 Best Window Companies in Winnetka, IL (2024 Reviews)

Are you looking to upgrade your windows? Our list of the top window installation companies can help you pick the right one for you.

We analyzed all the top-rated window companies in Winnetka and selected the best 20 based on:

  • Customer reviews
  • Window installation expertise
  • Popularity with home-owners like you
EcoWatch Local Advisors

By EcoWatch Local Advisors

Updated February 01, 2024

Why you can trust EcoWatch

Our panel of energy experts work tirelessly to create unbiased reviews and informative content to help homeowners make educated decisions. No other windows site has covered energy efficiency and sustainability as long as EcoWatch, which means we're going to help you find windows replacements that will save on your energy bill and put more money back in your wallet.

Although environmentally friendly energy sources like wind and solar are important when it comes to decreasing your carbon footprint, improving your house’s energy efficiency can also have a considerable impact on home energy conservation. Drafty windows can decrease your home’s energy efficiency by up to 30%, according to the Department of Energy. In Winnetka, that’s almost $295 a year that you could save on your power bills after making the switch.

That’s also bad for the environment, as the extra energy required by old windows increases your carbon footprint.

So if you’re constructing a new home, renovating or replacing your windows in Winnetka, you’ve found the best place to get started.

Best Availability

Renewal by Andersen

★★★★★
4.5
  • Great industry reputation
  • Member of US Green Building Council
  • Manufactures products in-house
Buy One Window, Get One 40% OFF
Get Estimate

Best Energy-Efficient Features

Champion

★★★★★
4.5
  • Many years of experience
  • Low prices relative to competitors
  • Limetime warranty
Buy 2 Windows, Get 2 Free
Get Estimate

Power Home

★★★★★
4.5
  • Uses eco-friendly materials
  • Well-trained, certified installers
  • Lifetime or lengthy warranty
Next-Day Appointments Available
Get Estimate

Best Window Installation & Replacement Companies in Winnetka

The EcoWatch team assessed dozens of providers that serve the Winnetka area to find the top window installation companies by our standards. The companies we’ve mentioned in this article passed our review standards for energy-efficient offerings as well as customer service, price, local expertise and beyond.

Window World logo
FAST QUOTE
as little as 30 seconds
Best Affordability

Window World

★★★★★
BBB Rating: A+
Locations: Nationwide
Founded: 1995
Pros:
  • Pros icon EnergyStar Partner
  • Pros icon Large serice area
  • Pros icon Low prices relative to competitors
  • Pros icon Great industry reputation
  • Pros icon Lifetime warranty
Cons:
  • Pros icon Quality of service will depend on your area

Window World provides windows expertise in Winnetka. This provider has 27 years of experience in the window installation business, and it has established itself as one of the most reputable companies in Winnetka.

If you’re looking for a company that is certified by the Environmental Protection Agency (EPA) and Energy Star and supports charities like St. Jude Children’s Research Hospital, Window World may be the right company for you.

Energy Efficiency of Window World Windows

Window World is an Energy Star partner offering a variety of energy-efficient windows. Note that not all of the company’s windows are Energy Star certified, so be sure to ask your Window World representative when inquiring about services.

How much does Window World cost in Winnetka?

Prices are not available on Window World’s website since the cost of window replacement depends on how many and what type(s) of windows you need. However, it's known for offering some of the most affordable window installations around. For more detailed information on pricing, you can ask for a quote from the company.

Renewal by Andersen logo
FAST QUOTE
as little as 30 seconds
Best Overall

Renewal by Andersen

★★★★★
BBB Rating: A
Locations: Nationwide
Founded: 1995
Pros:
  • Pros icon Great industry reputation
  • Pros icon Award-winning company
  • Pros icon Member of US Green Building Council
  • Pros icon Manufactures products in-house
Cons:
  • Pros icon No lifetime warranty
  • Pros icon More expensive than competition

Renewal by Andersen provides the best availability in Winnetka. This provider has 27 years of experience in the window installation business, and it has established itself as one of the most reputable companies in Winnetka.

If you’re looking for a company that uses in-home estimates and advanced digital tools to help you plan and visualize your project before getting started, Andersen may be the right company for you.

Energy Efficiency of Renewal by Andersen Windows

Renewal by Andersen is an Energy Star partner offering a variety of energy-efficient windows. Note that not all of the company’s windows are Energy Star certified, so be sure to ask your Andersen representative when inquiring about services.

How much does Renewal by Andersen cost in Winnetka?

Prices are not available on Andersen’s website since the cost of window replacement depends on how many and what type(s) of windows you need. However, based on customer feedback, you can expect to pay anywhere between $750 to $1,250 per window for an installation with Andersen. For more detailed information on pricing, you can ask for a quote from the company.

Universal Windows Direct logo
FAST QUOTE
as little as 30 seconds
Best Warranty

Universal Windows Direct

★★★★★
BBB Rating: A
Locations: Nationwide
Founded: 2002
Pros:
  • Pros icon Makes charitable contributions
  • Pros icon Manufactures products in-house
  • Pros icon Wide variety of products and services
  • Pros icon Lifetime warranty
Cons:
  • Pros icon Limited service area
  • Pros icon Some installations carried out by third-party contractors
  • Pros icon Quality of service will depend on your area

Universal Windows Direct provides the best warranty in Winnetka. This provider has 20 years of experience in the window installation business, and it has established itself as one of the most reputable companies in Winnetka.

If you’re looking for a company that has an industry-leading warranty covering products, parts and workmanship for life, Universal may be the right company for you.

Energy Efficiency of Universal Windows Direct Windows

Universal Windows Direct is an Energy Star partner offering a variety of energy-efficient windows. Note that not all of the company’s windows are Energy Star certified, so be sure to ask your Universal representative when inquiring about services.

How much does Universal Windows Direct cost in Winnetka?

Prices are not available on Universal’s website since the cost of window replacement depends on how many and what type(s) of windows you need. However, installations typically range from $225 to $425 per window based on customer feedback. That makes Universal Windows Direct more of a budget-friendly option for window repair and replacements. For more detailed information on pricing, you can ask for a quote from the company.

Window Nation logo
FAST QUOTE
as little as 30 seconds
Best for Residential Windows

Window Nation

★★★★★
BBB Rating: A
Locations: Regional
Founded: 2006
Pros:
  • Pros icon Award-winning company
  • Pros icon Manufactures products in-house
  • Pros icon Custom designs
  • Pros icon Wide variety of products and services
Cons:
  • Pros icon Installation not covered by warranty
  • Pros icon Limited service area

Window Nation provides the best residential windows in Winnetka. This provider has 16 years of experience in the window installation business, and it has established itself as one of the most reputable companies in Winnetka.

If you’re looking for a company that gives customers the opportunity to view products and to speak to a representative in person in its showrooms, Window Nation may be the right company for you.

Energy Efficiency of Window Nation Windows

Window Nation is an Energy Star partner offering a variety of energy-efficient windows. Note that not all of the company’s windows are Energy Star certified, so be sure to ask your Window Nation representative when inquiring about services.

How much does Window Nation cost in Winnetka?

Prices are not available on Window Nation’s website since the cost of window replacement depends on how many and what type(s) of windows you need. However, based on customer feedback, you can expect to pay between $300 and $525 per window installed, making it a more affordable option compared to competitors. For more detailed information on pricing, you can ask for a quote from the company.

Please note that the following companies are national, meaning the quality of customer service may depend on your local team. We have tried to be unbiased and transparent by listing pros and cons for every company.

More Window Companies in Winnetka

Renewal by Andersen of Chicago

Glenview, IL
4.8
★★★★★
  • Pros icon Free assessment
  • Pros icon Educational Website
  • Pros icon Good Customer Service
  • Pros icon Price Transparency

Services Offered

  • Service icon Skylights
  • Service icon Double-Hung
  • Service icon Custom Window Designs
  • Service icon Bay Windows
  • Service icon Window Replacement/Installation
  • Service icon Glass Doors

Website: https://www.renewalbyandersen.com/window-company/080-chicago-il/about-us
Address: 2300 Ridge Dr, Glenview, IL 60025
Phone: (847) 486-5680

Power Home Remodeling

Chicago, IL
4.4
★★★★★
  • Pros icon Good Customer Service

Services Offered

  • Service icon Energy-Efficient Options
  • Service icon Window Replacement/Installation

Website: https://powerhrg.com/
Address: 2500 W Bradley Pl Unit G, Chicago, IL 60618
Phone: (847) 916-5363

Window World Western Chicago

Lisle, IL
4.9
★★★★★
  • Pros icon Free assessment
  • Pros icon Educational Website
  • Pros icon Price Transparency
  • Pros icon Good Customer Service

Services Offered

  • Service icon Bay Windows
  • Service icon Glass Doors
  • Service icon Double-Hung
  • Service icon Window Replacement/Installation

Website: https://www.windowworldwesternchicago.com/
Address: 4646 Western Ave, Lisle, IL 60532
Phone: (331) 903-6873

Window Nation

Romeoville, IL
4.5
★★★★★
  • Pros icon Good Customer Service
  • Pros icon Price Transparency
  • Pros icon Educational Website
  • Pros icon Free assessment

Services Offered

  • Service icon Glass Doors
  • Service icon Custom Window Designs
  • Service icon Bay Windows
  • Service icon Energy-Efficient Options
  • Service icon Window Replacement/Installation
  • Service icon Vinyl Frames
  • Service icon Double-Hung

Website: https://www.windownation.com/chicago_showroom/
Address: 1263 Lakeview Dr, Romeoville, IL 60446
Phone: (815) 306-8024

EV Windows & Doors, Inc.

Des Plaines, IL
5.0
★★★★★
  • Pros icon Free assessment
  • Pros icon Educational Website
  • Pros icon Price Transparency
  • Pros icon Good Customer Service
  • Pros icon Timely Service

Services Offered

  • Service icon Metal Frames
  • Service icon Window Replacement/Installation
  • Service icon Glass Doors
  • Service icon Vinyl Frames
  • Service icon Wood Frames
  • Service icon Fiberglass Frames
  • Service icon Double-Hung

Website: https://evwindowsinc.com/
Address: 9344 Knight Ave, Des Plaines, IL 60016
Phone: (847) 612-8894

Royalty Windows

Glenview, IL
5.0
★★★★★
  • Pros icon Educational Website
  • Pros icon Good Customer Service
  • Pros icon Price Transparency
  • Pros icon Free assessment

Services Offered

  • Service icon Window Replacement/Installation
  • Service icon Vinyl Frames
  • Service icon Bay Windows
  • Service icon Double-Hung
  • Service icon Custom Window Designs

Website: https://www.royaltywindows.com/
Address: 4318 Regency Dr, Glenview, IL 60025
Phone: (847) 999-7920

Semko Inc.

Chicago, IL
5.0
★★★★★
  • Pros icon Free assessment
  • Pros icon Price Transparency
  • Pros icon Good Customer Service

Services Offered

  • Service icon Vinyl Frames
  • Service icon Window Replacement/Installation
  • Service icon Glass Doors
  • Service icon Bay Windows
  • Service icon Double-Hung
  • Service icon Energy-Efficient Options
  • Service icon Wood Frames

Website: http://www.semkoinc.com/
Address: 6259 W Touhy Ave, Chicago, IL 60646
Phone: (773) 631-1060

Beka Window Repair

Wheeling, IL
5
★★★★★
  • Pros icon Price Transparency
  • Pros icon Free assessment
  • Pros icon Good Customer Service

Services Offered

  • Service icon Bay Windows
  • Service icon Energy-Efficient Options
  • Service icon Window Repair
  • Service icon Tempered Glass
  • Service icon Glass Repair
  • Service icon Window Replacement/Installation
  • Service icon Double-Hung
  • Service icon Metal Frames
  • Service icon Vinyl Frames
  • Service icon Wood Frames
  • Service icon Glass Showers
  • Service icon Glass Doors

Website: https://foggywindowrepairs.com/
Address: 222 E Camp McDonald Rd, Wheeling, IL 60090
Phone: (773) 786-8821

Northwind Exteriors

Park Ridge, IL
5.0
★★★★★
  • Pros icon Price Transparency
  • Pros icon Good Customer Service
  • Pros icon Free assessment
  • Pros icon Educational Website

Services Offered

  • Service icon Window Replacement/Installation

Website: https://northwindexteriors.com/
Address: 508 W Higgins Rd, Park Ridge, IL 60068
Phone: (773) 998-4000

Siding & Windows Group

Glenview, IL
4.9
★★★★★
  • Pros icon Free assessment
  • Pros icon Good Customer Service
  • Pros icon Educational Website
  • Pros icon Price Transparency

Services Offered

  • Service icon Wood Frames
  • Service icon Energy-Efficient Options
  • Service icon Window Replacement/Installation
  • Service icon Fiberglass Frames
  • Service icon Vinyl Frames

Website: https://sidinggroup.com/
Address: 1112 Waukegan Rd, Glenview, IL 60025
Phone: (847) 251-4200

LEN Roofing & Remodeling

Northbrook, IL
4.9
★★★★★
  • Pros icon Timely Service
  • Pros icon Educational Website
  • Pros icon Free assessment
  • Pros icon Good Customer Service
  • Pros icon Price Transparency

Services Offered

  • Service icon Glass Doors
  • Service icon Window Repair
  • Service icon Custom Window Designs
  • Service icon Window Replacement/Installation

Website: http://www.lenroofing.com/
Address: 1240 Meadow Rd Suite 101, Northbrook, IL 60062
Phone: (847) 768-6000

Savocchi Glass Company, Inc.

Glenview, IL
4.9
★★★★★
  • Pros icon Price Transparency
  • Pros icon Timely Service
  • Pros icon Educational Website
  • Pros icon Free assessment
  • Pros icon Good Customer Service

Services Offered

  • Service icon Energy-Efficient Options
  • Service icon Metal Frames
  • Service icon Skylights
  • Service icon Vinyl Frames
  • Service icon Custom Window Designs
  • Service icon Custom Glass
  • Service icon Window Repair
  • Service icon Storm/Impact Windows
  • Service icon Glass Doors
  • Service icon Window Replacement/Installation
  • Service icon Glass Showers
  • Service icon Wood Frames
  • Service icon Mirrors
  • Service icon Fiberglass Frames

Website: http://www.savocchi.com/
Address: 3210 W Lake Ave, Glenview, IL 60026
Phone: (847) 446-3340

Scientific Home Services Ltd

Niles, IL
4.9
★★★★★
  • Pros icon Good Customer Service
  • Pros icon Price Transparency
  • Pros icon Educational Website
  • Pros icon Free assessment

Services Offered

  • Service icon Fiberglass Frames
  • Service icon Window Replacement/Installation
  • Service icon Window Repair
  • Service icon Double-Hung
  • Service icon Vinyl Frames
  • Service icon Wood Frames
  • Service icon Metal Frames

Website: https://www.shschi.com/
Address: 5639 W Howard St, Niles, IL 60714
Phone: (847) 752-0370

Forde Windows & Remodeling, Inc.

Northbrook, IL
4.8
★★★★★
  • Pros icon Free assessment
  • Pros icon Price Transparency
  • Pros icon Educational Website
  • Pros icon Good Customer Service

Services Offered

  • Service icon Energy-Efficient Options
  • Service icon Window Repair
  • Service icon Window Replacement/Installation
  • Service icon Wood Frames

Website: https://fordewindowsandremodeling.com/
Address: 3233 Arnold Ln, Northbrook, IL 60062
Phone: (847) 562-1188

Windows, Doors & Siding by Opal Enterprises Des Plaines

Des Plaines, IL
4.8
★★★★★
  • Pros icon Good Customer Service
  • Pros icon Educational Website
  • Pros icon Price Transparency
  • Pros icon Free assessment

Services Offered

  • Service icon Vinyl Frames
  • Service icon Energy-Efficient Options
  • Service icon Window Replacement/Installation
  • Service icon Double-Hung
  • Service icon Glass Doors
  • Service icon Wood Frames
  • Service icon Bay Windows
  • Service icon Fiberglass Frames

Website: https://www.opalexteriors.com/service-areas/des-plaines/
Address: 1239 Rand Rd, Des Plaines, IL 60016
Phone: (847) 979-9896

Aurora Apex Windows and Doors

Wheeling, IL
4.8
★★★★★
  • Pros icon Free assessment
  • Pros icon Educational Website
  • Pros icon Good Customer Service
  • Pros icon Price Transparency

Services Offered

  • Service icon Bay Windows
  • Service icon Vinyl Frames
  • Service icon Glass Showers
  • Service icon Wood Frames
  • Service icon Energy-Efficient Options
  • Service icon Metal Frames
  • Service icon Custom Window Designs
  • Service icon Window Replacement/Installation
  • Service icon Double-Hung
  • Service icon Window Repair
  • Service icon Triple Pane Glass
  • Service icon Glass Doors
  • Service icon Tempered Glass

Website: https://apexwindowwerks.com/aurora-doors-and-windows/
Address: 105 W Marquardt Dr, Wheeling, IL 60090
Phone: (847) 469-1544

Apex Window Werks - Chicago Window Repair & Glass Replacement

Wheeling, IL
4.7
★★★★★
  • Pros icon Educational Website
  • Pros icon Price Transparency
  • Pros icon Free assessment
  • Pros icon Good Customer Service

Services Offered

  • Service icon Window Repair
  • Service icon Wood Frames
  • Service icon Glass Doors
  • Service icon Metal Frames
  • Service icon Double-Hung
  • Service icon Custom Window Designs
  • Service icon Tempered Glass
  • Service icon Glass Showers
  • Service icon Vinyl Frames
  • Service icon Glass Repair
  • Service icon Energy-Efficient Options
  • Service icon Window Replacement/Installation

Website: https://apexwindowwerks.com/
Address: 111 W Marquardt Dr, Wheeling, IL 60090
Phone: (847) 716-2290

McCann Window & Exteriors Inc

Northbrook, IL
4.5
★★★★★
  • Pros icon Price Transparency
  • Pros icon Timely Service
  • Pros icon Educational Website
  • Pros icon Free assessment

Services Offered

  • Service icon Window Replacement/Installation
  • Service icon Glass Doors

Website: http://mccannwindow.com/
Address: 3375 Commercial Ave, Northbrook, IL 60062
Phone: (847) 562-1212

American Thermal Window Products

Chicago, IL
4.3
★★★★★
  • Pros icon Educational Website
  • Pros icon Price Transparency
  • Pros icon Timely Service
  • Pros icon Free assessment

Services Offered

  • Service icon Window Replacement/Installation

Website: http://www.americanthermalwindow.com/
Address: 5304 N Milwaukee Ave, Chicago, IL 60630
Phone: (773) 774-3131

Next Door and Window

Arlington Heights, IL
4.8
★★★★★
  • Pros icon Free assessment
  • Pros icon Price Transparency
  • Pros icon Educational Website
  • Pros icon Good Customer Service

Services Offered

  • Service icon Window Replacement/Installation
  • Service icon Bay Windows
  • Service icon Double-Hung
  • Service icon Glass Doors

Website: https://www.nextdoorandwindow.com/
Address: 718 E Rand Rd, Arlington Heights, IL 60004
Phone: (847) 398-8624
Winnetka Window Cost Calculator

Calculate how much you can expect to pay for window installation and replacement in Winnetka, IL using our customized window cost calculator.

Estimated Window Cost:
161 homeowners have requested a free estimate in the last 3 days.

Estimates will vary based on window dimensions and other unique factors to your home. Getting in touch with a local window installer is the best way to get an accurate cost estimate for your home.

How Installing Energy-Efficient Windows in Winnetka Saves You Money

When you upgrade to energy-efficient windows, you may see some perks, including:

  • Save on energy bills: Since energy-efficient windows reduce the amount of energy used to heat or cool your home, the switch can help you save about $295 annually on your energy bills in Winnetka.
  • Protect your valuables: Many Energy Star certified windows have low-emissivity coatings, which not only provide better insulation for your home, but also filter out damaging UV rays, preventing fading of your furniture, carpet and other valuables.
  • Reduce your carbon footprint: Reducing the amount of energy you use also lowers your indirect greenhouse gas emissions. You could reduce it by about 449 pounds.
  • Protect your investment: The older your home is, the more likely you are to benefit from switching to energy-efficient windows. Older homes tend to have windows that are outdated, drafty or maybe even damaged in some way. Updating your windows could help increase the value of your home if you decide to sell.

Estimated Cost of Window Replacement in Winnetka

Windows come in various shapes and sizes, so costs and services will differ considerably. Here are the typical costs and services that you’ll find from window installation companies.

How Much Do New Windows Cost?

Typically, Winnetka homeowners can anticipate their window replacements to range from $250 to $1,200. The most common installations sit at about $600. These figures are based on the specifics of your installation, like number of windows, size, the location of your home, material, type and more.

It’s important to note that windows with higher efficiency may cost more initially but can save you hundreds of dollars via returns on your energy bills. Investing in certified energy-efficient windows can save Winnetka homeowners $295+ a year when replacing single-pane windows.

Costs will also vary based on the material you choose for your window frames. Aluminum frames cost the least. They’re sturdy, light and maintenance-free, but provide poor insulation. Vinyl frames are somewhat expensive and provide good insulation. Composite frames made with wood fibers encased in plastic also provide good insulation and are moderately expensive. Wood frames cost the most and are the most in-demand. They’re also aesthetically pleasing and provide decent insulation for your home.

What Services do Window Installers Offer?

The first thing to ask yourself when considering a window replacement is: Should you get a full-frame installation or a pocket installation?

Full-frame installations require replacing the whole window — the sill, frame, trim and all. These are typically done when you want a different style for your windows or when it has a great amount of deterioration. Full-frame installations are more comprehensive and will increase overall costs. Pocket installations are on the simpler end and won’t carry as large a bill, as they entail simply replacing the window within its existing frame. But if the frame has any damage or rot, you should opt for a full-frame installation instead.

If you’re still trying to decide which kind of installation you need, you can ask your provider and get their advice. The choice mostly is influenced by how old the frames are and if there’s any damage present.

Best Availability

Renewal by Andersen

★★★★★
4.5
  • Great industry reputation
  • Member of US Green Building Council
  • Manufactures products in-house
Buy One Window, Get One 40% OFF
Get Estimate

Best Energy-Efficient Features

Champion

★★★★★
4.5
  • Many years of experience
  • Low prices relative to competitors
  • Limetime warranty
Buy 2 Windows, Get 2 Free
Get Estimate

Power Home

★★★★★
4.5
  • Uses eco-friendly materials
  • Well-trained, certified installers
  • Lifetime or lengthy warranty
Next-Day Appointments Available
Get Estimate

How We Choose the Best Window Installers in Winnetka

EcoWatch reviews differ from most reviews, as we look at these companies through a sustainability lens. We have assessed the top window installation companies in Winnetka mainly based on their energy efficient offerings, as the most sustainable option also benefits homeowners in many ways. Energy Star certified windows have been shown to cut your electricity bills by hundreds of dollars. Along with energy efficiency, our rating methodology considers the following factors:

Service Area

This one is self-explanatory, but we’ve chosen to highlight window installation companies that serve the Winnetka area so you can find the best window installation company near you.

Work Quality

When selecting new windows, the quality and variety of services can often play just as important of a role in insulation and performance as the brand of window you choose. We do give window installers more points if they offer high-quality products, but we also consider workmanship as reflected in customer feedback.

Customer Reviews

We analyzed trends in recent online reviews to determine the companies with the most customer satisfaction, weighted by sample size. Customer satisfaction may be the most important factor, as it reflects the quality of services across most other categories, including cost, warranty, quality of installation, quality of parts, professionalism and more.

Cost

Cheaper windows don’t necessarily mean better windows, but we know many of our readers would like to keep costs low when possible. When analyzing the prices of providers, we gave higher scores to companies with reasonable prices and accessible financing rather than “cheaper” services.

Warranty

Protecting your investment in new windows is important to many homeowners. That’s why window installation companies that have lengthy warranties for products, parts and labor rank higher with EcoWatch.

Years of Experience

Due to Winnetka’s climate, homeowners will want to mitigate low efficiency, water damage and rot. We factored in local experience to reflect the ability of Winnetka window companies to prepare homes for the climate. If a company has less than 10 years of experience, it loses points in this category.

Winnetka, IL Window Replacement FAQs

How much should a window install cost?

The national average cost of installing a single window is around $600 but can range between $200 and $1,200, depending on several factors. The price is often influenced by the location of your property, the size of the window and the type and material of the window. Also, bear in mind that energy-efficient windows may cost more upfront but can save you hundreds of dollars a year in energy bills.

What are the most common kinds of replacement windows?

There are several different types of windows you can get for your house, including slider windows, double-hung and single-hung windows, picture windows, awning windows, bay windows, casement windows and transom windows.

Can you install your own windows?

Even though you can install your own windows, doing so requires a lot of time and handiness. Hiring a professional can help ensure that the installation is done properly and that you won’t have to spend the time and effort to do it yourself.

Should I replace all my windows at once?

If your windows are greater than 20 years old, you probably need to replace all of them. At that point, they are typically less efficient, leakier and/or more damaged than new windows. Replacing your windows all at the same time will involve less paperwork and less time.