Alpen HPP Windows Reviews 2026
Alpen High Performance Products makes some of the best fiberglass windows on the market today. The company is based out of Colorado and began manufacturing high performance fiberglass windows and doors back in the early 1980s. Alpen HPP enjoys a very good reputation for quality windows and doors that are also quite expensive (as you would expect). Perhaps the biggest issue with the company might be finding a local company that carries the brand. Scroll down to read all of our Alpen Windows reviews.
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Our Verdict: If you have a local Alpen window dealer in your area, then you should absolutely get a bid on one of their high quality fiberglass windows and patio doors. Some of the best in the business - so why not? Related Topic: Alpen Window Prices
(Always Get 3 to 4 Local Price Quotes - And My Personal Advice)
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Alpen Windows Cost: $$$$$
(5 out of 5 Amongst All Fiberglass Windows)
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Page Sections
- Alpen HPP Introduction
- Company Information
- Alpen HPP Windows And Doors
- Alpen Warranty Information
- Homeowner Alpen Windows Review Section
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Alpen HPP Company Overview
The latest iteration of Alpen was "started" back in 2012 when Brad Begin, who is currently the CEO of Alpen High Performance Products, purchased the assets of Serious Windows (headquartered in Sunnyvale, California). The history is interesting and somewhat ironic. Robert Clarke started Alpen back in 1981 and operated the company until 2008, when it was acquired by Serious Materials.
Clarke was one of the main project managers in Serious Energy's biggest project, which was the government contract they received to replace the windows on the Empire State building - over 13,000 windows, can you imagine the cost of that project! When Serious Windows went bankrupt in 2012, Alpen HPP, led by Clarke, purchased the assets of Serious Windows and is now manufacturing fiberglass windows under that name.
According to Allison Ray at Alpen, the replacement glass for the Empire State building has already paid for itself in energy savings in under 4 years time.
Alpen Windows And Energy Efficiency
What windows does Alpen HPP manufacture and sell? Specifically, three window series for residential use. These include their Alpen Zenith and Tyrol series, as well as the more commercially available Aspekt+ series. First up the Zenith - the Zenith series is a fiberglass window frame that is constructed using high quality components, glass, and hardware. The double hung window will deliver a U-value of .26, condensation resistance of 68 and an air infiltration of .09. These numbers should stay as true as any over the years.
Alpen also sells the Tyrol series windows and doors, which is a fiberglass-reinforced vinyl (uPVC). The Tyrol series also uses quality components, glass, and hardware. The double hung window delivers the following performance numbers: U-Value .26, 64 Condensation Resistance, and a .09 air infiltration rating. The numbers here are quite close to the Zenith series.
The Alpen Aspekt+ is U.S. passive home certified and is made from a hybrid fiberglass and uPVC polymer sash. The casement delivers a .16 U-value, which honestly is as low a number as I've ever heard of. (The lower the better the window, fyi).
Alpen Windows Warranty Coverage
The Alpen warranty covers the original buyer from any manufacturing defects for as long as they own their home. The warranty covers any subsequent homeowner for a period fo 10 years from the date of installation. New owners must inform Alpen HPP of the title transfer and pay a small fee. All in all, it’s not all that strong of a warranty, which is surprising given the quality of Alpen HPPs products.
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Homeowner Alpen Windows Reviews
Below we have listed all of our homeowner questions and answers on all aspects of Alpen HPP and their windows and doors. If you have any additional questions, don't hesitate to ask.
Dane - Site Editor
Alpen High Performance Fiberglass Windows
| Product | Project Detail | Editor Takeaway |
|---|---|---|
| Alpen Fiberglass Windows And Patio Slider | $17,000 total for 10 windows and 1 patio slider | Approximately $1,545 per opening |
| Alpen Zenith Casement | 0.10 U-value and 0.01 air infiltration rating | Premium performance numbers for a fiberglass window |
"I’ve been evaluating several high-performance replacement window options and brands here in Denver. At the moment, I’m leaning toward Alpen primarily because the thermal performance specifications, which seem kind of amazing. I’d appreciate any feedback you could provide regarding product quality, durability, serviceability, or installation-related concerns."
"My project includes 10 black fiberglass-framed windows along with a large patio slider. The total package cost is approximately $17,000."
"I’d also be interested in recommendations for other manufacturers operating within this same performance category, particularly companies offering fiberglass window and patio door systems with similarly aggressive thermal values and energy efficiency metrics."
Barry, Homeowner - from 2026
Editor's Advice:
Barry, you have certainly identified a quality brand in Alpen fiberglass windows. Their Zenith casement window, for example, delivers a leading industry 0.10 U-value and 0.01 air infiltration rating — pretty much the best numbers you could ask for. Product quality and durability are second to none.
There are no installation-related concerns per se, although your home configuration and installation requirements can always influence the final result. The next piece of the puzzle is finding a quality installer, but Alpen generally does a good job of using qualified dealers to represent their products.
Finally, the price point sounds very fair for such a high-quality fiberglass package. I definitely think you have half of the equation solved.
Dane — Site Editor - from 2026
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San Diego Replacement Window Options
| Window Brand | Material Type | Editor's Takeaway |
|---|---|---|
| Renewal by Andersen | Composite | Strong sales presentation and premium product, but often one of the highest-priced options |
| Milgard | Vinyl / Fiberglass | Common West Coast brand with broad dealer availability and several series options |
| Marvin Fiberglass | Fiberglass | One of the stronger fiberglass options to consider in California |
| Anlin Windows | Vinyl | Well-regarded Southern California vinyl option with strong overall reputation |
"Dane, thanks for the informative videos. I'm in San Diego, 92115, looking for my home's 18 windows to be replaced. I'm leaning towards fibreglass. If you have any recommendations for window installers I'd love to hear them."
"I've had quotes from Milgard, Home Depot, and Renewal by Andersen but haven't been impressed by any of them. Renewal sounded the most convincing of the bunch but they're oh so expensive. Many thanks."
Richard, Homeowner
Editor's Advice:
Richard, the main issue with fiberglass windows on the West Coast is often availability and price. Marvin is one of the few fiberglass window brands that I think is definitely worth your time in California. Alpen and Inline are generally harder to source there, although it never hurts to double check local availability.
Alpen makes some of the best fiberglass windows on the market from a performance standpoint, but dealer coverage can be limited depending on your location.
I would also try the form on our site to see what installers are available in your zip code. Anlin is another brand that immediately comes to mind for Southern California and is generally very well regarded.
Dane — Site Editor
Alpen 625 Series Cost
| Window Series | Total Quote Installed | Average Installed Cost |
|---|---|---|
| Marvin Infinity | $74,428 | Approximately $2,255 per opening |
| Pella Impervia | $92,296 | Approximately $2,797 per opening |
| Renewal by Andersen | $123,024 | Approximately $3,728 per opening |
| Kolbe Forgent | $70,529 | Approximately $2,137 per opening |
| Kolbe Vista Luxe | $99,750 | Approximately $3,023 per opening |
| Alpen 625 Series | $46,627 + estimated $20,000 installation | Approximately $66,627 total, or $2,019 per opening |
"Dane and Tim: I am looking for a little guidance on window selection for Castle Pines, CO. The elevation is 6500 feet and the majority of the windows are either south or west facing. I am replacing all the original wood clads and doors in a 30-year old home. There are roughly 30 windows and 3 sliding doors."
"Bids have been all over the place. After reading reviews on your website, I contacted Alpen because they are made nearby. Surprisingly, they are the low bid even with triple paned windows. I would purchase the windows directly and have my GC install them. He has not worked with Alpen products before. I have heard good things about the Alpen product but less than stellar reviews on customer service."
"I have also been told the locking mechanisms tend to be stiff and harder to operate as a result of the energy efficiency. The runner up to the Alpen product would be the Kolbe. I like the Vista Luxe line but would likely be priced out. I am not sure that I like the Forgent better than the Alpen. Triple Pane Windows Cost"
"Based upon the bids below, can you provide any additional insight?"
Brett, Homeowner
Editor's Advice:
Brett, from what I know, Alpen makes a very good fiberglass window series and it may be one of the strongest performance options on your list. Given the elevation, south and west exposure, and interest in triple pane glass, Alpen makes a lot of sense from an energy-efficiency standpoint.
The main concern is not really the product itself, but the installation arrangement. Since your general contractor has not worked with Alpen before, I would make sure he is comfortable with the installation requirements before moving forward. For a project this large, the installer matters just as much as the window.
I would spend a little more time looking into Alpen for your own peace of mind, especially customer service and dealer support, but based on the bids you listed, the Alpen 625 Series would be my frontrunner.
Dane — Website Editor
Alpen HHP vs. Thermo-Tech
The companies are steering me away from Hayfields the last yr they have had delivery problems orders not complete no screens for months after the order comes suppliers just got an email from the new CEO that said they know they have problems and will be working to resolve in the future and they are sorry for there problems that they knew that they had.
With that being said I check the pricing on Thermo-Tech windows to match the Alpen HHP #'s U-Value.0.19, R-Value 5.26, CR 69 these numbers match the Alpen HHP exactly and these cost $8500 and with installation its $10,500 to $11,000 that's $7000ish less I have Soft-lite coming next week Monday and the Minnkota window bid really leaning towards the Thermo-Tech's same warranty.
Robert - Homeowner - from 2022
Alpen Zenith Series ZR6 vs Milgard Ultra
Dane, in the process of replacing approx 50 windows and 5 doors in my home in Arvada Colorado. I currently have 20+yr old Vetter windows and do to a hail storm insurance is covering about 1/2 of them so I’m going to replace them all. I have a contractor who regularly uses the Milgard fiberglass windows and likes them but then I have another that uses Alpen fiberglass and likes those.
I live about 10 miles from the Alpen manufacturing and corporate site so I was able to visit them and tour the factory. Although I’m as far from an expert as you can get I was impressed with Alpen and the fact they are local. That being said I respect my contractor and his thoughts about Milgard. Looking for a 3rd party perspective that know the industry. I’d appreciate your thoughts. Thanks.
Randy - Homeowner - from 2021
[Site Editor's Answer]
Randy, the Alpen Zenith Series ZR6 is the better performer by quite a bit. The U-factor, R-value, and air infiltration or AI are very impressive. See the link that I sent you from their website. Have you looked at our alpen windows reviews page? Good place to start.
Data doesn't lie (although some of these manufacturers can get inventive with how they frame the data, but not these two in question...) Alpen Performance data.
I'm not exactly sure the Milgard Ultra numbers, but there is simply no way that they stack up to the Alpen Zenith Series ZR6, which is nearly unbeatable. Having said that, I actually like the Milgard Ultra fiberglass window a lot. Just not when up against the Alpen model.
Dane - Site Editor - from 2021
Alpen Windows For A Passive House
I want high SHGC windows for a passive house. Could you help?
Richard - Homeowner - from 2015
[Editor's Response]
Paul, thanks for the question, this is one question we are hearing of with more and more frequency. While Passive Houses are less popular in the United States compared to Europe and Canada, but this is changing, albeit slowly. In terms of price and availability, here in the U.S. we will be looking primarily towards Canadian window manufacturers who either ship to the states or who have some limited distribution in the U.S. (typically in the Northern States near the U.S. Canada border, although a passive home can obviously be located anywhere.)
Whoever you are using to build your home should be somewhat familiar with these companies. Passive house windows will all be custom ordered based on the direction they face in order to maximize the SHGC or passive heat that they are able to collect. To this end, make sure to ask about the timeline to order and ship the windows to the job site. Here are three companies off the top of my head that specializes in passive home technology...
Alpen Windows
Intus
Klearwall
Tim - Site Editor - from 2015
Alpen Windows vs Marvin
We're in Virginia and recently had a quote on Marvin Integrity fiberglass windows with all ultrex frames.
We are also considering Alpen 525s windows.
Lastly, we looked at HiMark casement, which were less expensive than the first two.
Any opinions are much appreciated and love your alpen windows reviews.
Daniel - Homeowner - from 2013
[Contractor Response]
Daniel, Marvin makes a very solid fiberglass window and the Integrity all ultrex is a nice model.
Compare replacement window reviews from the most popular brands:
I like the Alpen fiberglass window more and think the numbers speak for themselves. They tend to be quite expensive.
The HiMark casement is an excellent vinyl window and certainly one to consider. I might go with the HiMark myself, although Alpen makes an excellent window as well.
Peter - Contractor - from 2013
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About The Author
Dane is the site editor of Replacement Windows Reviews and has worked in the window and door industry for more than 40 years. He spent nearly two decades as a professional window installer before transitioning into consumer education and window review analysis.
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