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Your Windows Your Way

We are Colorado’s most trusted source for replacement windows, doors, and siding. 
Book your free design consult or continue reading to learn more about our available products and services.


New windows provide beauty, protection, insulation, and value to your home. Click to view our premium collection of replacement windows hand-selected by a Colorado local.


Extend a warm welcome to every visitor through a beautifully crafted front door. We offer a variety of options to match the style, design, or function you’re looking for. 


Improve curb appeal, protect your home from the elements, lower your energy bill, and dampen outside noise all with the help of LP SmartSlide siding.

Local Expert Service From Our Family To Yours

Nex-Gen Windows & Doors is the local favorite among Colorado homeowners.


Known for premium materials such as Infinity from Marvin, our Lifetime Installation Warranty, and exceptional service, we’re equipped to help with all your window, door, or siding needs.


Click to learn more about the products, services, and team members that make Nex-Gen Windows & Doors the right choice for your next home improvement project.

Why Settle?

Don’t settle for high energy bills and outdated designs in your home. Many of competitors present inaccurate quotes, use scare tactics and are pushy to get you buy products that are not right for your home. When it comes to installation, they can be messy and damage your property.

You Deserve More.

What Others Are Saying

Jill HansenJill Hansen
15:42 29 Aug 23
I would highly recommend this company. We had these windows installed throughout our house and they look great. The installation was pretty quick. The few issues that came up, the company was quick to resolve.
Laura BrownLaura Brown
19:45 25 Aug 23
We had Nex-Gen replace our windows and sliding glass door. Neil Horn was very professional. He answered my calls promptly, addressed every concern I had and has checked multiple times to ensure that we are happy with the work. Roberto and his crew did a good job on the installation. We are very pleased with our new windows and door and would highly recommend Nex-Gen.
Mary BettersMary Betters
18:14 24 Aug 23
I highly recommend Nex-Gen if you are looking for quality attractive windows and doors. I just had them out for the second time to install two doors and two windows. They replaced my other windows and doors a few years ago. I really noticed the reduction in heat and cold and just love the way they look so I knew Nex-Gen would be my go-to Company. I can't say enough about all the staff that I worked with. Justin, the sales rep, was great at coming up with options that met my budget while not sacrificing my wants. He even helped me out with some non-related home issues while here. Steve and Arthur worked tirelessly doing a meticulous job on the installation, making sure I knew everything about the products and made sure everything was cleaned up after the work. Neal did a great job managing the project and ensuring that I was totally satisfied while encouraging me to call with any problems no matter how small. You won't be disappointed if you hire Nex-Gen!
Nicki MeyersNicki Meyers
20:49 23 Aug 23
They have done it again! Reuben and his crew put in a new window, and my house looks amazing! They took out a fake bay window and transformed the entire look of my house. I can not say how wonderfully respectful, honest, and trustworthy the entire company is...Chris, Janice, Thomas, Reuben, etc....! If you need windows, doors , or now siding, these guys are the ones I would call first (it will be your only call).
Steve BlandaSteve Blanda
16:55 26 Jun 23
NexGen installed windows and a patio door for my father in-law. He was very impressed with not only the quality of the windows but also the way Neil handled everything from start to finish. He also thought Roberto and his crew did an amazing job installing. They were , polite, clean and explained everything to him. The quality of these windows and the professionalism of this team showed him that he went with the right company to handle his window needs. He highly recommends NexGen Windows and Doors.Chuck Reese - Greeley.
Melissa BartonMelissa Barton
20:02 12 Jun 23
After getting several quotes for windows, buying some not-so-great ones from a place who did a TERRIBLE job and doesn’t follow up or provide any customer service, we decided to do a lot more research about windows and companies here in Colorado. After getting more quotes and doing a TON of research on the best windows for the extreme weather, we found Marvin Infinity windows to be the best and NexGen has an unbeatable warranty. It is truly lifetime (there is no asterisk) and can even be transferred if you sell your home. Neil Horn was great in the sales process, he came to the house and listened to our needs and worked within our budget and was very honest about what would be best for us and our home. We also met at the store and looked at all the windows and selected those that would be the best for us. It was so nice to have the hands-on experience. Neil also kept us updated on the status of the order and was even here the day the windows were installed. Neil, Don and the entire crew were so good about making sure we knew how to operate the windows and were careful in walking through to inspect and make sure everything was in top shape. The crew was VERY clean and respectful. This was a wonderful experience. Thank you NexGen and Neil Horn. After a few days we already notice a noise reduction, temperature regulation and ease of use. We LOOOVE our new windows. We HIGHLY recommend them.** Update** We had an issue with our window and Neil came out on Memorial Day to check out our window and take measurements to order our replacement.

Our Formula for Success


Let us know when we can stop by to view the space, discuss your needs, and provide you with a free quote.

Expand, intersect, pointers, screen resolution, spread


Compare available styles, designs, and functions with an experienced design consultant.


Relax knowing the installation will be quick and painless with no mess or damage left behind.

A Colorado Staple Built on a National Reputation

Year History of Replacement Experts

Successful Installations

Families Served

Customer Satisfaction Rating

Not only are we a trusted face in your community — we are the trusted partners of a national brand, Infinity(R) from Marvin(R). This window manufacturer ranks #1 in customer satisfaction for its quality and longevity and considers us Diamond-level partners in the windows industry nation wide.


We don’t hide behind a nationally accredited brand service standard — we let our service speak for itself.


If you’re looking for a local recommendation for windows, door, or siding replacement, schedule your free quote or give us a call today.

We understand that Colorado homeowners have to endure more than their fair share of extreme weather conditions.

Your home is your biggest investment. Protect this investment with products and services which have proven to outlast the competition in the harsh Colorado elements.


Hail, wind, extreme temperatures, and high altitude will take their toll on the exterior of your house from season to season which means that eventually you’ll be faced with the decision to replace or repair your windows, doors, or siding. And if you’re like most homeowners, it may be your first experience in doing so.


You deserve to work with a team that offers decades of direct insight into which brands can withstand the elements along with proven installation techniques to keep your home looking beautiful and your family feeling safe and comfortable.