Alpen High Performance Products makes some of the best fiberglass windows on the market today. The company is based in Colorado and began manufacturing high performance fiberglass windows and doors in the early 1980s. Alpen HPP enjoys a very good reputation for quality windows and doors that are also quite expensive. 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.
My Take On This Company: 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.
(Always Get 3 to 4 Local Price Quotes)
Overall Rating:Alpen Windows gets a 4.9 out of 5 stars based on 11consumer reviews below.
Dane - Site Editor - Original Publish Date - March 15, 2015 Page Last Updated On September 29, 2025
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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.
What They Sell
Alpen HPP sells 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 Warranty Information
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.
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
San Diego Replacement Window Options
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 - from 2023
[Site Editor's Answer]
Richard, the only issue with fiberglass is availability and price. Marvin is one of the only fiberglass window companies that I would say is worth your time out on the west coast. Alpen and Inline are not available there (check but I believe this is correct.) Alpen makes some of the best fiberglass windows out there.
I would try the form on our site to see what else there is in your zip code. I'm not sure what we have in 92115.
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?
Alpen 625 Series: $46,627 + installation (estimated to be $20,000)
Brett - Homeowner - from 2022
[Website Editor Reply]
Brett, so you probably know more about Alpen than I do. From the little I know, they make a very good fiberglass series -- quite possibly better than any of the windows on your list. I know NOTHING about the Kolbe Forgent so I can't comment. I would spend some more time looking into Alpen for your own piece of mind, but that would be my frontrunner.
Dane - Website Editor - from 2022
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.
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...
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.
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.