How to Interpret Ratings for Replacement Windows

When shopping around for replacement windows, it’s easy to
become distracted by all the options. First you have to decide which window
style works best for your home. Next, you’re thumbing through a variety of
color and finish options. Then, just when you think you’ve got it all nailed
down, you’re staring at a bunch of technical-sounding terms like U-Factor, VT
Rating and DP Rating. What does all of this mean?

Who sets the standard for window ratings and
why do they matter?

All new windows and doors are rated by the National
Fenestration Rating Council (NFRC). This rating is used to determine whether a
product qualifies for the Energy Star program. If the preset standard is met, that
indicates a strong performance in areas such as thermal efficiency (U-Factor), durability
(DP Rating), and sound transmission (STC Rating).

What’s the difference between R-Value and U-Factor?

Both the U-Factor and R-Value are used to measure thermal
performance of window glass. When looking at the U-Factor, a lower rating is
best. You want a rating between 0.17 and 0.39 for optimal performance in cold climates.
When looking at the R-Value, higher numbers are best; a rating between 2.5 and
6 is considered a quality rating.

R-Value was the industry norm prior to a tightening of the
standard in 2008 by the NFRC. Now, U-Factor offers a more accurate representation
of the window’s performance.

Why is that? R-Value measures the efficiency of the glass
center only. U-Factor considers the entire glass along with the window frame
for a more complete picture of performance.

How should I compare VT ratings?

Visible transmittance (VT) measures the amount of light that
is transmitted through the window. If you want more natural lighting inside of your
home, then you want a higher VT score. These numbers range between 0 and 1. For
example, double and triple-pane windows usually land between 0.30 and 0.70.

Before you compare the VT rating of multiple windows, keep
in mind that the VT rating does not measure the glass alone. This rating also
considers the thickness of the window frame and sash, glass coatings, and the presence
of window grids or munitions. So, look at the VT rating of like-featured
windows for an accurate comparison.

Do thicker window frames have a better DP rating?

The strength of the window is measured by the Design
pressure (DP) rating. If you live in a storm-prone area such as a hurricane zone,
then you want a widow with the highest DP rating possible—at least 15-50.

You might assume that thicker window frames have a higher DP
rating. However, that is not always the case. What’s more important is the
material used to manufacture the frame, so look for the DP rating instead of relying
solely on frame thickness.

Do triple-pane glass windows have the best STC rating?

If you live in a noisy area and you want windows that block
unwanted sound pollution, then STC rating is important for you.

Sound Transmission Class deals will efficiency and sound proofing.
The higher the rating, the better performance you will get. Standard windows
usually score between 18-20. Windows that are designed with sound transmission
in mind fall between 28-32; some go as high as 48.

Sometimes windows with multiple glass panes offer better sound
proofing, but that is not always the case. It depends on the thickness of the window
glass, gas fill, and other manufacturing features. Ask for the STC rating to
make sure you’re getting the noise-blocking benefits you want.

Are there other ratings I should know about?

The above ratings are important when looking for an
energy-efficient, durable, and quiet window, but that’s not all. These ratings
are also very useful:

CR Rating: Condensation resistance is an
important energy efficiency marker. The higher the score the better the
performance; look for a CR rating between 30 and 80.

Air Infiltration: If you live in an area
with strong winds, then this rating is important for you. Look for a rating of
0.30 cfm/sqft or lower. This measurement considers how many cubit feet of air can
pass through your window during a constant 25-mph wind.

Do you need high-performance replacement windows?

Choosing the right windows for your home can be tricky, but
the window contractors at Texas Remodel Team are here to help. We offer a
variety of stylish windows that are highly efficient, durable, and made to
withstand harsh hurricane winds. Contact us today to learn more or to request a
free window installation cost estimate!

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