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!

If you’re looking for a window company right now, the best advice we have is to join Angie’s List.  For just a couple bucks you can get a 1-month membership and it’ll be worth much more than a caramel macchiato in the long run.  You can find the best pricing for Angie’s List on the internet right here

If you’re already a member of Angie’s List or if you’re just not going to join (despite my ringing endorsement), you can find our suggestions for the best companies in your area right here.

Update: We now have more recommend LOCAL window companies than ever before.   Click here to see who we recommend in your town.  It's 100% free.  You'll thank me.  There is no better resource; you're going to love it.  See for yourself right here.  

39 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. 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.

  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.

  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).

  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.

  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

  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.

  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.

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