Windows are a crucial part of any home, and selecting the right windows for your home is important. But with all the different types of windows on the market, which is the best choice for you?

One factor to consider when choosing windows is the U-factor score. What is U-factor, and how can you use it to select the best window for your home? This article will help you understand the U-factor score and how you can decide which window is best for your needs and climate.

Keep reading to learn more.

What Is U-factor?

The U-factor measures the energy efficiency of different house components (materials) such as skylights, doors, and windows.

National Fenestration Rating Council (NFRC) devised this measurement system under their voluntary program for testing, certifying, and labeling doors, windows, and skylights. All windows certified by them bear an "Energy Star" label.

The Energy Star label highlights that a certain window meets energy-efficiency criteria and would help you save money on energy bills.

But what exactly does a U-factor measure?

A U-factor is a measure of the speed at which non-solar heat passes through a window. It combines elements like solar heat gain coefficient, air leakage, and sunlight transmittance.

Remember, the U-factor doesn't only represent a window's glass' or glazing's ability to conserve heat. It is, in fact, the overall performance of all window parts collectively: glass, frame, and spacer.

A window with a high U-factor rating is less energy-efficient and will not insulate your home, as well as a window with a low U-factor rating. This is why homeowners look for windows with low U-factor scores when they want to improve their home's energy efficiency.

Windows with low U-factor scores will keep your home warmer in the winter and cooler in the summer. In other words, they will help regulate the temperature in your home and make it more comfortable.

What Is A Good/Bad U-Factor Score?

Let's try to understand what a good or bad U-factor score is.

The U-factor score for windows ranges from 0.20 to 1.20. The lower the number, the better insulated or energy-efficient is your window. However, windows with a U-factor between 0.30 and 0.15 are known to be the most energy-efficient.

Since U-factor considers the entire assembly (glass, glazing, frame, and spacer) of the window, single, double, and triple pane windows have different U-factors.

Out of the three, triple pane windows tend to have the lowest U-factor rating, near 0.15. On the other hand, double pane windows' U-factor scores are around 0.30.

This makes triple pane windows the most energy-efficient type, followed by double and single pane or regular windows.

However, the rest of the assembly components, like the glass coating and inert gas in the spacer, can also impact a window's U-factor score.

This means a double pane window with better glazing (or Low-E coating) and the leak-proof inert gas may have a lower U-factor than a triple pane window with poor coating and inert gas performance.

What Are the Benefits Of A Low U-Factor?

Now that you know how a U-factor is measured and what factors affect it, you must be wondering why having a low U-factor is essential.

Here are some benefits of having low U-factor windows:

1. Improved Thermal Regulation in Your Home

As we mentioned earlier, U-factor measures how well a window regulates the heat in your home.

Low U-factor windows will be ideal for you if you live in an area with extreme weather conditions, whether hot or cold.

They will help keep your home comfortable by maintaining an ambient temperature.

2. Saves You Money in the Long Run

Investing in windows with a low U-factor will help you save money on your energy bills in the long run.


Since low U-factors are highly energy efficient and regulate temperature better, they will reduce your reliance on your house’s HVAC systems. This reduced dependence on HVAC will ultimately reflect on your energy bills, and you will save money in the long run.

Bonus: Since you'll be using your HVAC system less, it will also help increase its lifespan.

3. Reduces Your Home's Carbon Footprint

Low U-factor windows are great for the environment and your contribution towards sustainability. These windows help you save money and reduce your home's carbon footprint.


By reducing your reliance on artificial heating and cooling, these windows will help you conserve energy. And by saving energy, you'll also be reducing your carbon footprint.

In simple words, you will use less artificial energy to keep your house warm or cold when you have windows with low U-factor ratings.

Besides, low U-factor windows will get you comfort, increased home value, and a sense of satisfaction.

How To Choose U-factor According To Your Location And Climate?

Now that you know what the U-factor is and why it's important let's learn how to select a window with the right U-factor for your home.

Here are a few things to keep in mind while choosing the U-factor of your windows:

1. Your Climate

Climate directly impacts your window's U-factor choice, so it's the first thing you'll consider.

If you live in a hot climate, you'll need windows to keep your home cool. Or, if you live in a cold climate, you'll need windows to keep your home warm.

2. Your Home's Insulation

The second thing you need to consider is your home's insulation.

If your home is well-insulated, you can get away with windows with a slightly higher U-factor.

But if your home is not well-insulated, then you'll need windows with a low U-factor to make up for it.

3. Your Home's Orientation

Finally, you need to consider your home's orientation.

If your home is oriented to get a lot of sunlight, you'll need windows with a low U-factor to keep the heat out.

On the other hand, if your home is oriented so that it doesn't get a lot of sun, you may get away with windows with a slightly higher U-factor.

General Values:

Remember, cold-weather climates usually require a lower U-factor than warm or hot climates. You might have to go for a U-factor rating of 0.30 or lower in cold climates, while a 0.60 U-factor might be sufficient in hot climates.

And, if you live in a moderate or mixed climate area, a U-factor score of 0.32 to 0.35 might be the ideal.

So, be careful when choosing your windows; a wrong U-factor could lead to inefficient performance and higher energy bills.

October 08, 2022 — Della Wang