Window Ratings Explained

Efficient replacement windows and doors

The very first thing to remember as you’re starting to sort through window ratings is that just about every aspect of a window’s performance can be relatively easily quantified.  If you’re the kind of person who likes to get into the details of these things you’ll love shopping for windows.  Just remember to keep an eye on the big picture.  Don’t let yourself get all distracted by a 0.02 difference in one rating or another.  Some companies will really try to get you focused on this rating or that in order to justify their price.  Try not to lose sight of the forest for the trees as they say.

Remember that all features of a product only really matter if they affect the window ratings.  For example, if a salesperson tells you that his windows are “better” because they have foam filled frames ask him what the u-factor is.  If it’s better than another product you’re considering then it’s better.  If the u-factor is not better that foam isn’t doing you any good.  I guess an easier way to say this would be that you don’t care much about foam in frames or coatings on glass, windows filled with magic gas or anything else.  You care about an efficient window.  The method to get to the efficient product really isn’t all that important.  The results are the important part and the results are easily quantified.  There’s no need to take someones word for it.

So what are the basic window ratings to keep an eye on?  They are:

We’ll also look at organizations related to window ratings including:

I’ll put together specific posts on each one of these window ratings explaining what they mean, what levels are considered good or great, where you’ll likely find the best bang for your buck and any tips or tricks for interpreting what they’ll actually mean to you.

This is an example of an NFRC sticker that comes on every replacement window. It shows the ratings for this individual window.

If you’re not a physics teacher and not all that interested in delving into the minutia here, you may be looking for a way to tell if a specific product is “pretty good” without spending a tremendous amount of time learning all about the specific window ratings and that logic makes sense.  To accomplish that goal, look for a product that meets the energy star requirements for your climate zone.

There are already products available that meet the  current energy star guidelines and that would be something to consider.  You can also learn about the structural performance of a product by looking at its AAMA rating.  Gold is the best, then silver, etc.  All major products are AAMA certified so if you come across one that isn’t or if a company won’t tell you the rating that would be a major red flag.

energy star program for replacement windows in 2014 and 2015
Energy Star is a helpful program to determine if a replacement window is energy efficient.

If a product meets the 2024+ energy star criteria and it’s AAMA gold certified then you’ve got yourself a pretty solid window.  If you want to get a deeper feel for how one product compares to another dig on into the window ratings.  Keep an eye on future posts for LOTS of details!

Other posts you might find helpful:

For now you can find the best replacement windows reviews here and you can also find information on common window sales tactics to avoid right here.

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83 thoughts on “Window Ratings Explained”

  1. Spacers have not yet been reviewed . I am in the market for windows and don’t know which spacer to opt for. Can you help me.

    1. We’re working on a pretty long post with all sorts of info on various spacers, but it’s a little ways from being finished. Which options are you considering? We’ll be glad to offer any info that we can!

      1. I would like to see you compare a double to a triple pane sealed unit at 2 PM in the morning when there is no sun and it is 30 below. As we all no in the winter we get maybe 6 hours of sun on a good day. 1/3 of the winter.That means that there is 18 hours of no solar gain.All the test seem to be doing solar deflection which is a summer time inviroment . And that is only s/e to s/w when the sun is high in the sky for the right angle.The more air spaces between you and out side would mean more R-Value. If this is not the case we might as well go back to 2×4 walls verses 2×6 walls. If you add up the square foot of all your windows it would equal one of the wall in your home.R-Value in R-Value.Lets look at the real facts.

        1. I’m not sure what you’re saying. Triple pane is definitely a great option in the North. Are you thinking it’s not?

    2. Stay away from metal, you something like a warm edge non conductive spacer, you’ll pay more but it will be worth it

      1. Stay away from Window World out of Cape Coral, Florida. They promised windows installed 3 Months ago and then have the nerve to be rude and very nasty as we try to ascertain when our window might be installed. Would never use them! I even asked for a
        Small change in our order over a
        Month ago and they refused. Terrible customer service. Hope their windows are decent if they ever get them installed!

        1. You’re right Stanley, window world is a franchise and has a specific target demographic for client
          They want homeowners who buy on price alone, a customer that would look the other way when it comes to quality in return for a bargain price
          They hardly honor warranties, and their products are sub par
          I’m sorry to hear you have problems with them for installation
          Try to get out of the contract of you can, they’re gonna say “no” however your lawyer may find a way with it, there are start dates and completion dates they may need to legally bind by
          If they treat you like this now when you owe them money, imagine how they’re gonna treat you after they get fully paid
          Good luck either way you go
          Jay E

    3. Can anyone help me out? I’m currently comparing prices and ratings between two window companies. They’re very similarly priced and rated except that one window company has a 0.04 air infiltration rating and the other (which my general contractor prefers to work with) has a 0.3 AI. My GC says not to place too much importance on that difference and that they may have gotten lucky or did an intentionally super tight seal for the certification, and further, who knows what the actual product will be. He also says that it’s more important that they are properly installed and jammed. Is he right? We’re talking 35 windows for my large house!

      1. The testing process is very strict and very uniform across all companies so I’d say there’s basically no chance that anyone got lucky or that anyone cheated on the testing. The rules are very strict. Someone claiming otherwise is potentially trying to convince you to buy the product that they make the most profit on.

        What window brands are you comparing and what’s your zip code? We may be able to make a recommendation.

  2. Ply Gem “warm edge” or “warm edge plus”. Apparently, the first is metal and the latter is nonmetal–less conductive?

    I wanted Alside Mezzo, but I have contacted 3 contractors and can’t get a quote.


    1. The non-metal spacer options can be a pretty good value depending on the price you get from your local window company. It would help a little to find out the real name of the product. I would bet the warm edge plus is also called Super Spacer. This is a pretty solid product with a good track record. You might confirm with them that it is this product before placing an order.

  3. Hi there. I have gotten. 3 quotes on windows and am still not sure what to do. I would like to talk to someone who can point me in the right direction.. Like what type of windows? Sliding/double hung/triple pane.. I didn’t think there would be so much to consider.. Please help

    1. Well, it sounds like you need a reputable local person to come by and help. Try Angie’s List. I know folks are hesitant to spend a couple bucks, but I promise you it’ll be worth it. You can see our thoughts on Angie’s List here. It’s a great way to find someone who will treat you fairly and offer good advice.

  4. In the NFRC listings found via the CPD code, what does “Gap Widths” refer to? Is that the spacing between the glazing or the outside dimension of the glazing?

  5. I have 20 year old MW wood windows . I am looking at MW 600 double hung for replacement . Neither ply gem nor MW is covered. What do you think of this choice?
    Thanks for your time and I believe your site is very beneficial to the consumer.


    1. HI ROBERT, YOU DON’T NEED TO YELL! Just kidding, we do have Home Depot window reviews on the sort list, but we’re still finishing up the Lowes replacement windows reviews first. You can see some details on the Simonton replacement windows on our Simonton page here.

    2. Maybe this post gets you too late, but stay away from Home Depot brands since they are designed to be replace in just a few years, unless of course this is a flip property then most people don’t care about installing sub par materials in a house they won’t keep

  7. I am considering Mathews Brothers Clara Starrett and Softlite Element/Imperial LS triple pain double hung windows for my New England coastal home. I can not find any reviews on the Clara windows. Can you help on the Clara Starrett and/ or give your thoughts on one vs the other?

    1. To be honest I’ve never heard of Matthews Brothers Clara Starrett windows. My time in Maine is limited to one trip to Portland from Boston and I don’t have too much time for looking around.

      I did just ship some Revere windows to a friend who has a cabin outside of Portland. Maybe we’ll get up there one of these summers and I’ll check out the Matthews Brothers options. Sorry I’m not much help on that front.

      I do think the Soft-Lite windows are pretty nice. They’re often sold at hefty prices, but that has more to do with the companies selling them than Soft-Lite.

      The folks at Soft-Lite have not been too helpful with us when we’re working on the site, but that’s not really related to the windows.

    2. Be careful when choosing a window brand in New England, the extreme heat and cold will destroy a low end window quite rapidly, you will need a good frame and a good glass warranty, if you care about heating or cooling the home, stay away from argon filled windows

      1. Hi Jay, you know companies have been offering argon filled windows in New England for many many years without any trouble right? I know the commission is probably higher on krypton, but that doesn’t mean it’s actually better. If you have any data or concrete info send it on over. If not, lets try to stick with the facts.

      2. I am really late to this party, but I gotta ask after reading your comments, are you Jay Johnson?
        You sure do sound like him from his many youtube videos; much of the same misinformed crap on his videos like what you posted here.

  8. I’ve recently received bids for windows configured two different ways. Standard, they come with Argon fill and an Intercept spacer. For ~$400 (for 9 windows) I can upgrade to Krypton and a Super Spacer. It makes a .02 U-Factor difference per window. All of these windows meet the 2014 Energy Star guidelines. The ones with Krypton would meet the 2015 guidelines as well. My instincts tell me to save the $400 and not worry about such a small difference, but I don’t know the real-world effect this would make in our house. We live in the Pacific Northwest, so the weather really isn’t all that extreme.

    Do you have any advice as we’re mulling our options?

    1. I typically do recommend picking windows that meet the current Energy Star guidelines, but it is just a number. If you do want to meet that standard there should be options that don’t involve krypton gas. It gets expensive and it doesn’t make that much of a difference (as you’ve noticed).

      1. Wrong, there’s a world of differences between argon and krypton filled windows
        Here is where lack of research can get you in trouble
        Yes, that .02 difference is a Grand Canyon
        First, if you’re playing golf and you are an excellent player and a terrible player, the accuracy of the swing is by 1/32 of an inch, little things matter,
        Also, no company ever can assure the customer they will get argon in their windows at installation, the warranties will say that under “performance” because that gas dissipates very rapidly
        Where Krypton stays longer not only providing longer energy savings but also since the gas is denser it provides higher energy efficiency, it’s like having one layer of insulation with argon, and 2 layers of insulation with Krypton,

        So yes, the small difference between a u factor .23 and a u .17 is huge HUGE!!!

        1. Hi Jay, thanks for chiming in. I don’t believe any of that. Do you have any data to back that up? Feels like the kind of story you’d hear in a sales training seminar.

          1. Any gas present in a window will dissipate
            The denser, heavier the gas is, the slowest will dissipate
            Those are not sales seminar tales, those are basic properties and concepts, do you need me to prove that? Or Einstein, Franklin or Newton did it for you already, pull any company, let’s say pella, look under Argon, what does it say?
            Look under Marvin, when it comes to energy performance, what does it say?
            I can let you prove my point anytime 🙂

          2. If the gas were to leak out, would something else need to leak in? If air fills the space you see condensation and that would be covered under the warranties of most larger manufacturers. I think saying windows with Krypton gas seal better than windows with Argon gas is not based in reality. Do you have any info to back that up? If so send it on over. If not, it’s probably better to not spread fake news.

          3. Of course, argon dissipates, air comes in, most frames from upper scale companies use silica or other hydroscopic materials to keep moisture away from the inner panes, fake news? Really? If you’re not ready to be awaken is one thing, another is show signs of passive aggression
            The silica will keep moisture away but only for a few years, so after the inner gas is gone the glass will remain free from condensation, fogginess, or any build up.
            Window dog, if you’re uninformed about windows, I can help you, but please ask me questions or challenge one of my points with an open mind, other wise this back and forth will seem like a sand box fight instead of a quest for the truth.
            By the way, have anyone here including yourself downloaded any warranties from the big companies, did you get to read them?

          4. You’re right that it’s beginning to feel like a sandbox fight. I’ve been in the window business for a little while now and I’ve read plenty of warranties. If you’re not in the business you might want to find a different hobby.

          5. That’s cute! hobby? That’s what your going for bud?
            Does it really matter if I’m in the industry or not when I happen to know more about brands, performance, warranties, PHYSICS, type of material, internal components, screen types and screen frames options, etc, you know, just some basic about windows, again, if you’re just trying to promote your brand then I’m sorry, I’m in the wrong place, if you truly want to help people, I am here to help as well, obviously this is your website, so if you think I’m a troll for challenging you when you’re wrong, then the quest for the truth will be tainted by your wrong comments, wether you even believe what you’re saying or this is just an act
            I’d like to believe I know windows, and if you’d like, please challenge it, I’m just here to help

          6. After all of these comments I’m having a hard time believing you’re not in the window business. Why would you advocate for a particular sales model if you’d just a window customer who has been doing some googling?

          7. The window dog, does it really matter wether I’m in the industry or not? Is your ego that in the box that you seems insulting if someone who is not in the industry can possibly know anything about windows, and god forbid challenge you on some points? Or maybe here is someone that is an insider, so you can pull a fast one on me, and that bothers you.
            Either way, most people here are not window experts so they look up info trying to find some clarity in this foggy messed up window market, most things are being built with planned obsolescence in just a few years or times of use, windows are no different, so it’s not one size fits all type of shoe, the perfect window for me may not be the perfect window for you, the the ideas of suggesting a window brand without having a needs analysis is silly, one doesn’t go to the doctor and tell the doctor what he needs and self prescribe himself right?
            Same here, the first thing the doctor does is to ask questions, tries to understand why and how they can benefit the most, I hope you can at least agree to that, as far as the sales tactic, to each is own, some build their cost of business into their price, some low ball themselves, some over price things and some give discounts for saving time, please don’t tell people only one way is right and the other are scams, you’re creating paranoia, not helping here Dan

          8. So you are in the window business? That makes more sense. When you lied about that before I was a little skeptical. How long have you been selling windows? That definitely explains some of your positions.

  9. I am puzzled about the window pricing I keep seeing online. We have some ordinary size windows and a few really large ones. I got pricing from 6 companies and they were all within 7 percent of each other. Our normal size windows will cost $2,297 each to replace and the large ones are around $3,500 each. This includes full frame replacement, completely staining and replacing interior trim and replacing and painting exterior trim. Since I have six companies involved, I would think the pricing should be representative of what is available. The total for the whole house is $55,000. The companies are on Angie’s list and no complaints on Where do I find the $500 to 1,000 dollar windows installed pricing everyone is writing about? We are in Wisconsin.

    1. You’re asking for a little more work than a typical replacement window project, but that pricing does still sound a little heavy. Which brands of windows are you looking at?

      1. I have bids from Sunrise vinyl, Andersen E series, Pella Architect series, Marvin ultimate next generation, Weather Shield, and a second Marvin bid. All different companies and yet extremely close on price.

    2. Of you’re planning on staying in that house for a long time, don’t shop on price, shop for quality, then once you find a window you believe belong in your home, find the price and if they are not affordable at this time, save, there’s no discount that will satisfy you by buying the wrong windows and have regret

  10. I’m looking to buy Windows from Window World and wondered what the difference between a series 3000 and a series 4000 picture window or can you tell me the difference

    1. They offer different windows in some stores than others and they call them all by the same or very similar names so it can be hard to tell the difference. Did they tell you who makes the windows they were offering?

  11. Can you clarify methods of installing replacement windows for stucco buildings? The two methods promoted seem to be (1) BLOCK INSTALL where the old window is removed, leaving half of the old fins and the new window (without fins) is just set into the window frame and caulked all around (sometimes with a flange to cover the stucco) OR (2) FIN INSTALL, where the window comes with fins and the old fins are fully removed and the new fins are reattached to the studs/frame and then caulked. Both require that some restuccoing be done but #2 requires more. Is one better?

  12. Been waiting over 9 weeks for replacement windows. Warranty. Now had storm damage to pic window still waiting. Below 0 they frost up hollow frames not good in cold or hot would not recommend this window. It’s contractor grade

        1. Silverline are low grade windows, that’s why they fail, research the materials of the frame, that’s why those fail

  13. I am trying to decide between replacing my windows with Pella Enhanced vinyl double hung for $12,500 or another local company that gets “A ” rating reviews on Angie’s List that uses Quaker windows. I’ve not heard of this brand but it is $3000 less than Pella for essentially the same level of window. It is a company that has been in business for decades. Do you know Quaker and what can you say about the brand? Many thanks.

    1. I don’t know Quaker, but the larger brands like Pella and Andersen don’t always offer the best value in my opinion.

      1. I don’t think all Pella windows are horrible, but it’s true that their lower end Pella products seem to be pretty low end.

        1. Low end is low end, is the frames are gonna warp, there’s no insulation on the frames, the argon is not guaranteed to be present when the windows are installed, how can any of those windows be anything but low end? Anyone?

          1. I’m not a huge Pella windows fan so you can’t talk me into defending them. I do think their 350 model is perfectly nice.

          2. You just defended them but saying they were nice, nice looking? Perhaps, nice performing? No way, worth the money? Maybe for a garage or a shed, never for the interior of a house
            Again, read their warranty

          3. You probably wouldn’t use these windows on the interior of a house. Your comments are getting harder and harder to follow.

  14. So I have a question may be silly but worth asking. I own a house and most of the windows in it are newer windows all vinyl. Now I was curious if I could take the double pane sashes out and replace them with triple pane sashes. I have a feeling it’s a big fat no due to the weights in the frames if I heard that right somewhere else?

    1. If you know the manufacturer of the windows you probably could order triple pane sashes to replace double pane sashes. One factor to remember will be that you’ll also need new balances or the windows won’t stay up. The triple pane sashes will be a little heavier so the old balances won’t hold them up.

      That’s usually an easy thing to change as well so not that big of a deal. If you don’t know who manufactured the windows it’ll be about impossible to get triple pane glass in them.

  15. What windows can you recommend for the Green Bay, WI area with the accompanying winters? What would be your top 5? I am not interested in the most expensive, just the best value.

    Thank you.

  16. I am trying to figure out the best window replacement between the Simonton ASURE and the Mi 1555 Series. Both are vinyl windows. I am interested in the best quality and functionality between the two for the Atlanta area. Thank you!

    1. Those two brands are lower end ones, the question that should be asked if one is right for you is, what are your goals? How many years are you trying to get out it? Do you care about energy efficiency? Is it for a rental unit? Is it for your forever home?
      Knowing things like that, it could help identifying which window can be better for your project, not all windows are made equal 🙂

  17. What is your opinion on Berkshire Elite from Revere triple pane vs. simonton madeira 7500 triple pane? The difference is looking like about $2,000 so wondering if that is worth it or not for the Berkshire.

    1. I defininltey think the Berkshire Elite is a nicer option than the Simonton. You get much better (lower) air infiltration rates and upgraded hardware to name a few advantages. We’ve dealt with the Berkshire Elite line for a while and Simonton is generally not a product I would carry. Good luck!

  18. I live near the coast outside of Houston, and am interested in strong impact-resistant windows. If cost were no factor, I think I would want a glass package something like Cardinal IG Sea Storm with LoE-366 (or 452+?) on surface 2, or comparable. (See right-most sample in Fig 50-2 on p. 51 of this document:

    I suspect that a request like that makes up a tiny fraction of the window replacement market, and that I will find very few manufacturers who will build me a window like that. Any who will, will likely be exorbitantly priced.

    Is there any way for me to get more educated about which manufacturers might build a window like that and what it would cost, without calling installers and asking them?

    I’m concerned that 19 out of 20 installers might just roll their eyes and try to explain why a different product they carry will be better for me. And it might be…or they just might not have a product that meets my desired specs and they’re just trying to sell me what they happen to have.

    Any suggestions on how to pursue this?

    I’m also wondering how dark/colored/distorted such a glass package might be, and am worried that even if I could find someone to build me that window, I might not be able to see it in person before ordering.

    1. Whoops–I had the 2015 version of that document open; the comparable illustration in the 2020 version I linked to is labeled “Insulating Laminated” in Fig 5-4 on p. 51.

      1. Hi Jim, every window company in Houston will be familiar with impact windows as they make up a decent percentage of the market in certain parts of town. I would suggest not falling in love with one glass manufacturer as most will have impact options and they’ll all meet the same standards and have similar or the same efficiency ratings.

        I’d say a good first step is to find a well regarded window company and call them to see if they offer impact windows and what type they carry. That’ll get you moving in the right direction.

        We do have a recommended window company in Houston. You can find them in this section. I don’t know off the top of my head if they carry an impact line but it would give you a place to start.

  19. Many thanks for the reply!

    I did take a look at your recommended installer, but they are 90 minutes north of me and at least one website indicated I was outside of their service area.

    Unlike in FL where storm-rated glass is required and so everyone carries it, a lot of Houston installers have (surprisingly) no mention of impact or storm-rated glass on their websites, much less any details like whether it’s IG or just laminated. I’d prefer to approach an installer with some level of information/education rather than completely ignorant, but I’m finding it tough to get familiar with what’s available on my own.

    Thanks again for the reply!

    1. Ok, Impact windows are required in a large portion of the Houston market. You might try searching for TDI Windstorm windows.

  20. I need to replace 17 double hung windows. I got two quotes that are about ~$13k for Provia Endure EN600 and Vytex Fortis. Both installers seem to be reputable in this area and the performance ratings look close. Do you have any additional insight into these two brands?

    1. Hi Keith, I don’t know any window installers to recommend in Sarasota, but perhaps someone else will chime in with a suggestion. As for window models, there are a limited number of impact window options. PGT is big in the area with mixed reviews. Alside offers an impact window and Mi does as well. I’d start by trying to find a good installer or dealer that you’re interested in working with and then see what he’d suggest in terms of window manufacturers.

      1. I live on the Treasure Coast in Florida. I’ve spoken with 3 contractors and 2 sell PGT and CGI. The other is offering Custom Window Systems. When I search websites in my are I see PGT and CGI. I haven’t read good things about CWS. Most contractors are telling me I need double pane, one says I don’t and that as long as the window meets HVHZ standard that “sacrificial “ piece of glass is not necessary. I just get more confused. He also suggested aluminum and the others say vinyl. What to do?

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