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When It Comes To An Airtight Window, You Need Two Things: Perfect Installation & An Impeccably-Designed Window

Here’s How We Provide Both In Spades

Poorly designed double hung windows are a huge source of air leaks in many Charlotte homes. And that’s really bad news for your energy bills—air infiltration in your windows can run up utility costs in a big way.

In this article, I want to tell you more about air infiltration in double hung windows, how it happens, and why Zen Windows has the most airtight double hung windows in the industry (and it’s not even close!).

First, let’s start with what air infiltration actually is.

Window Air Infiltration 101

Energy Star rates air infiltration of individual windows. You can find this rating on a window’s NFRC label under Air Leakage (AL). Here’s what the label looks like…

NFRC Label

NFRC label. I’ve circled the Air Leakage (AL) rating.

The Air Leakage rating measures how much air will enter a room through the product itself (not around the actual frame—I’ll come to that in a second). This rating is expressed as a number between 0.1 and 0.3, with lower numbers being better. The number itself refers to how much air leakage occurs in a window per minute. For example, a window with a 0.23 AL rating will leak air at a rate of 0.23 Cubic Feet per Minute (CFM).

As a rule of thumb: 0.1 is exceptional, 0.2 is pretty good, and 0.3 is average and considered the industry standard. Anything higher than 0.3? Avoid!

What Causes Double Hung Window To Leak Air?

Air can leak through the sash meeting rail, sash perimeter & sill of a double hung window.

Air can leak through the sash meeting rail, sash perimeter & sill of a double hung window.


Air infiltration can occur in the actual window or around the frame. Since double hung windows are not fixed (meaning they contain parts that can open and close), there are multiple spots where air infiltration can occur. Here’s a look:

Poorly designed double hung windows will leak air because they don’t have the built-in airlocks, weather stripping, and barriers required to stop air from forcing its way into your home. Without these components, air will push between the sash meeting railings and around the perimeter of the sash.

Why We Have The Most Airtight Double Hung Windows

The Air Leakage rating on an NFRC label only goes as low as 0.1. That’s unfortunate because it cannot capture how amazingly efficient our vinyl double hung windows are—0.01 to 0.07!

That’s right. Our vinyl double hung windows are over 10 times more airtight than the NFRC’s best rating.

How? Because our windows specially designed to block air and are packed with weather barriers that go FAR beyond industry standards. These components include…

  • High-density Comfort Foam
  • Ultra-Smart triple-fin weather stripping
  • Soft-Seal straddle gasket
  • Dura Sill’s double-walled sill dam

To put how airtight our double hung windows are into perspective, consider this:

  • WOOD double hung windows from brands like Pella, Marvin, and Andersen have an average AL rating of 0.23. This means our vinyl double hung windows are 23 times more airtight. In other terms: Just one wood double hung window leaks the same amount of air as TWENTY-THREE of our vinyl double hung windows.
  • The best VINYL double hung windows from “big-name” brands like Alside, Simonton, and Champion have an AL rating of about 0.15. This makes OUR vinyl double hung windows 15 times more airtight.

How Does Installation Contribute To Window Air Leakage?

As previously stated, the AL rating measures only the proficiency of the window itself. It does not take into account potential air leakage around the frame. But even the best vinyl double hung windows in the world will leak air if they are not properly installed. If the installation is crooked… or the opening for the window isn’t cut PERFECTLY… or the sill flashing is done wrong… the window WILL leak air. End of story.

This is why it’s best to go with a professional, well-reviewed window company to install your double hung windows in Charlotte. Here are a few things to consider when researching window companies…

  1. Do they have plenty of reviews and customer references?
  2. Does there website contain an ample number of project photos, so you can get a sense of their work?
  3. How long is the company’s warranty? Does it include both labor and materials, and is it free from fine print?
  4. Does the company have the proper liability insurance?
  5. Is the owner easily accessible if you have questions? Are they actively involved to ensure the highest-quality installation?

At Zen Windows Carolina, our No Deposit protocol GUARANTEES you the absolute best installation. Why? Because you don’t pay us a dime until we’ve installed your windows and YOU are satisfied.

For more reasons why we’re Charlotte’s go-to company for vinyl double hung windows, explore the links below:

Thank you!

Brian Zimmerman
Owner

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