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.

Even though I’m writing this in February of 2014 there are already products available that meet the 2015 energy star guidelines and that would be something to consider.  You can also learn about the structural performance of a product by looking at it’s 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 2015 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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82 responses to “Window Ratings Explained”

  1. JimR Avatar

    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. JimR Avatar

      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. thewindowdog Avatar

        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.

  2. JimR Avatar

    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. thewindowdog Avatar

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

  3. Ngi Rifkin Avatar
    Ngi Rifkin

    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. thewindowdog Avatar

      Hi there, what’s your zip code? We may be able to help out with a recommendation.

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