Best Vinyl Windows: Qualities that Make the Best

An overview of qualities you should look for to determine the best vinyl windows for you

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Pop quiz: What’s the best car?

Pencils down.

However you answered this question is probably the right answer--the right answer for you, anyway. You might have said a 1965 Ford Mustang, with classic looks and a beefy engine, but poor handling compared to current generation cars. Or you might have answered a 2010 Toyota Prius, noting its exceptional gas mileage and small stature. Whatever your answer, the “best” is largely dependent on what qualities matter the most to you.

In this respect, windows are a lot like cars. Sure, there are popular brands such as Andersen, Pella, Simonton, Republic, and CertainTeed, but a particular brand doesn’t necessarily translate to the best vinyl windows. “Best” is a combination of qualities that suit your needs. The four qualities you should give the highest priority are U-factor, Solar Heat Gain Coefficient, Visible Transmittance, and Air Leakage. Numerical values associated with these factors will be listed by the manufacturer on the windows. Generally, a lower number is better.



U-factor determines how well your windows prevent heat in your home from leaking outside. It generally ranges from .2 to 1.2. The lower the u-factor, the better your windows are at keeping air inside. The best vinyl windows have a u-factor of about .2 and sometimes lower. For a window to be Energy Star certified, its u-factor must be .35 or below.

Note that u-factor differs from r-factor, which refers to how well the windows insulate.

Solar Heat Gain Coefficient:

Solar heat gain coefficient is similar to u-factor, but refers to an opposite form of heat prevention. Solar Heat Gain Coefficient designates how well the windows deflect heat from the sun with a value from 0 to 1. Think of it as a percentage. For example, solar heat gain coefficient of .25 means 25 percent of the heat from the sun’s rays will find its way through the window. The best vinyl windows will have a low solar heat gain coefficient.

Visible Transmittance:

Visible transmittance is similar to solar heat gain coefficient, but instead refers to the amount of light that slips through the window. Like solar heat gain coefficient, it’s measured on a scale of 0 to 1, with a lower number referring to a lower percentage of light allowed through the window. Note that you can also lower visible transmittance with aftermarket coatings or films. Opinions vary person to person about how much light should be allowed in through the window, so the best vinyl windows have a visible transmittance that fits your desires.

To get more information about window replacement price estimates, see our main artilce on the cost of new panes here.

Air Leakage:

Air leakage refers to the amount of air that slips through the window and into your home. Generally, air leakage falls between .1 and .3 with the lower numbers indicating less air allowed in. This is important an areas with frequent high winds--windows with high air leakage can become whistling sirens on windy days. Again, the best vinyl windows have around .1 air leakage.


Condensation Resistance Factor:

Condensation resistance factors refers to how well the window prevents condensation, a build-up of moisture. Unlike the previous four qualities, the best vinyl windows have a high condensation resistance factor, preferably at .60 or higher.


The best vinyl windows, of course, will also look the best to you and match your home in a way that gives it the most aesthetically pleasing appearance possible.

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