What Are R-Values for Windows? Why Do They Matter?

Windows. Why are there so many measurements and numbers when it comes to the window world? After all, we’re not in math class. We’re just trying to upgrade our home.

There’s U-values and R-values and SHGCs and more.

We’ve discussed thoroughly on what U-values are when it comes to windows, but what the heck are R-values? And why does your window salesman keep talking about it?

What Do R-Values Measure?

Let’s explain R-values in easier to understand terms because it could get a bit complicated.

First, the definition. R-values are a measurement of a material’s ability to impede heat flow. The material could be a wall, floor, roof, door, window, and more.

Now, some examples. We know that some materials such as aluminum and stainless steel that get really hot when you leave it in a hot pot for too long. This means it doesn’t resist heat flow very well. These materials have low R-values, which is not good for a home’s insulation or energy efficiency.

Other materials, like wood and glass, can resist heat flow much better. This gives them higher R-values.

Basically, a higher R-value means that the material will be better at resisting heat going into your home in the summer and letting heat go in the winter.

Bigger R-value = BETTER.

Why Do R-Values Matter to You?

Now that you know what an R-value is and that higher is better, why should this even matter to you?

If you’re anything like the average homeowner, you’re looking to decrease your energy bills and improving your home’s energy efficiency by buying better windows.

You’re tired of hearing your HVAC units turn on constantly throughout the hot and cold season. I get it, I’m tired too. In fact, I hear it right now on this warm summer day.

An R-value will tell you if your new windows have a higher resistance to heat transfer.

This means your AC and heating units won’t turn on as often because you’re not losing all that energy through your windows. Huzzah! You’ve saved some electricity.

Once you understand that U-values and R-values just tell you how good a window performs when it comes to heat transfer, everything gets a lot easier to understand.

How to Find R-Values of Windows

Unlike U-values, R-values aren’t typically just written down on a window’s label.

You could ask for this information from your window manufacturer or company. They’ll have it readily available.

But what if you’re just browsing your local home improvement store like Home Depot or Lowe’s?

In this case, get your phone and calculator out. It’s time for some math! Don’t worry, it’s super simple.

window label
Image via NFRC

You’re probably looking at a label like this one the window that you’re thinking of buying.

Take the top left number, the U-value, which is 0.35 in this case. Now, divide 1 by 0.35. You get 2.86.

That’s it! That’s all the math you need to do.

R-Values and U-Values: What’s the Difference?

All of these values to look at… which one matters more?

Good thing for you, they’re almost basically the same. Well, not really. But with one, you can calculate the other.

Both of these measurements are used to measure a window’s thermal performance. How well they do transfer heat? Or how bad?

U-values measure how much heat is transferred and at what speed. It measures heat flow. A lower U-value is better.

R-values measure the material’s resistant to heat flow. A higher R-value is better.

R-values and U-values are inversely related. This means to get one from the other, you just take the inverse.

Here’s how you do that.

calculate u value and r value

How to Improve R-Values

There are many ways to improve R-values. Here are some features to look for in new windows if you’re shopping around:

  • Double-pane or triple-pane glass – Triple-pane windows will have better U-values but also will cost more than double-pane windows.
  • Gas-filled windows – Using an inert gas such as argon will decrease the amount of heat that your windows transfer.
  • Low-E coatings on the surfaces of your window glass – These microscopic coatings on your windows will reflect more heat off the glass’s surface.
  • Frame material – Wood, fiberglass, and vinyl frames have better insulation than materials such as aluminum, which transfers heat quickly.
  • Thickness of glass – Thicker glass transfers heat slower.

All you have to remember is higher R-value is better, and lower U-value is better!

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