The Most Important Replacement Window Efficiency Number of All

Posted on August 03, 2016

replacement window efficiencyIf you have a tire that has three holes in it, and you just plug two of them, what have you got? That’s right, a flat tire!

Let’s finish off our discussion about drafty windows. A quick review…

  • The NFRC tests all new replacement windows for Air Leakage. This number is one of several listed on the sticker that should be attached to each window when they are delivered to your home for installation.
  • The NFRC says that there are a range of Air Leakage rates.
  • The NFRC allows window manufacturers to decide whether or not to publish their Air Leakage number on their stickers.

These three things confirm that just because you buy a new replacement window you won’t necessarily solve your drafty window problem. Otherwise there would be no need for testing, nor would there be a range of numbers. Also, there’s the question that we asked last time regarding what reason that a manufacturer would have for not publishing their number.

When you take all these things together it’s clear that the Air Leakage rate may be the most important replacement window efficiency number of all when it comes to evaluating the different choices of replacement windows for your home.

Remember the conversation about how even a 1/16” gap anywhere in the window assembly is the equivalent of taking a brick out of the side of you home? Keep that in mind as you think about the fact that there’s three things that every window manufacturer/home improvement contractor will tell you about their windows…

  • Their window frames are the best
  • Their glass is the best
  • They look the best

The thing is…there’s another “leg” to that stool and it’s the Air Leakage piece.

Replacement Window Energy Efficiency is About More Than Just Glass

If you had 20 windows in your home and replaced them with a window that looked awesome, and had great glass and frame, yet were still missing bricks from each room of your home, what kind of return could you possible expect on your new home window investment?

So, how can you tell whether or not the new replacement windows that you are thinking about for your home will truly fix the draftiness issue that you are experiencing?

Unfortunately, it won’t be the sticker. Even if a manufacturer chooses to publish their number, the NFRC allows them to publish the number as <=.30. Without getting too far into the weeds, this number is the maximum allowable in new residential construction. It’s also additional “proof” that all new windows won’t necessarily fix your problems with drafts.

Here are three ways to determine whether or not any window product that you are evaluating is going to fix your issue, or that window is the third hole in your tire.

  • replacement window efficiency and draftsSash slop—This is one of the easiest ways to evaluate. Take the double hung window sample that the contractor brings in your home to demonstrate, lock it down and then try to move the sashes up and down. Any movement indicates “sash slop” and is a result of higher tolerances and lower quality requirements in the manufacturing process. It doesn’t take much to create a 1/16” gap.
  • Interlocking sashes—This is one of those situations that something that looks and sounds reasonable isn’t. The contractor or dealers salesperson will show you, when closed, how the top and bottom sash “lock” together. They may even try an old trick where they stick a dollar bill in, close the sashes and ask you to try to pull the bill out. A closer look will reveal the problem with interlocking sashes—either edge. Due to the way a window is constructed the interlock can only go so far. The problem: the outside edges are where air typically comes in. Most of the products with interlocking sashes offer an extra “tell”—extra weatherstripping at the edges where the interlock stops.
  • Third party proof—Window products that provide the best air leakage results not only publish their numbers, but provide the contractors and home improvement providers that offer their product, third party validation of these numbers. It’s one thing to say you have great numbers in your company-produced literature, it’s another thing to provide third-party proof to allow a potential customer to easily verify what you are saying.

Sunrise Windows engineers their products to be more airtight, offering several different features that contribute to one of the lowest published air leakage rates available on the market today. You’ll find virtually no movement when doing the “sash slop” test, no interlocking sashes on any of our premium products, and you can find our published air leakage numbers for each product type here. Go to the nfrc.org website and use the CPD #’s supplied in this document to verify our, up to ten times better than the maximum allowable, Air Leakage rates.

I think we’d agree that regardless of how great the frames and glass are, maybe the most important replacement window efficiency number is the Air Leakage rate.

 

 

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About the Author

Joseph Mills

Joseph Mills

Joe Mills is the Director of Marketing for Sunrise Windows and Doors. He has spent almost 15 years working with homeowners helping them envision and design home improvement projects. He is proficient in assisting homeowners through their entire buying process, including helping them do the proper research, what signs to look for to minimize a homeowner’s risk, understanding the in home selling process and once the decision is made, how the installation process will work. He has written a consumer-oriented book called “How To Buy Vinyl Replacement Windows” that can help window buyers make educated choices.