What Is a Good U-Value for Windows?

Mar 24 2021 Posted By Ontario Window Reviews

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What Is a Good U-Value for Windows?

New developments in window technology give property owners more options than ever before. And thanks to the dedication of top-notch window companies to provide the best options, no one needs to compromise style, clarity, or sturdiness just to have energy-saving windows. 

Energy-efficient modern windows that offer advanced insulation and protection from solar radiation are available in various sizes, delightful styles, and can come with sturdy hardware that requires little maintenance for years to come. 

U-value windows pertain to windows that have a good u-value rating which corresponds to insulation power. U-value, aka U-factor, is the rate by which non-solar heat transfers through the window. The lower the U-value, the better the insulation that the window can give. 

However, it’s important to understand that U-value is only one of many energy-performance metrics that help window buyers to make the best choice for their homes and office spaces. 

So if you’ve ever wondered what u-value in windows is all about, why good insulation is important, what a good u-value range is for the Canadian climate, and what other energy-performance metrics you need to keep an eye on, you’re in the right place! This comprehensive article tells you all you need to know. 

Let’s get started! 

Woman sitting on a chair beside an energy-efficient window

What are Energy Performance Ratings?

Energy performance ratings are indicated on windows that are designed to be energy-efficient. Windows are considered “energy-efficient” if they help to minimize the usage of artificial heating/cooling in the home or property. To accomplish the previous objective, the window must be able to insulate well and/or protect the interior space from various kinds of solar radiation. 

Energy performance ratings give buyers a good idea of how much insulation and/or protection from solar radiation they can expect from a window. 

Do All Windows Have Energy Performance Ratings and Indicate a U-Value Rating?

Essentially, all windows have a U-value or U-factor. However, it is more common to find the u-value rating, along with other energy performance ratings, on windows that are ENERGY STAR®-qualified. 

NFRC vs. CSA Energy Performance Ratings

The ENERGY STAR® label tells you that the window is energy-efficient. But to compare between different choices of energy-efficient windows, you’d need to look at the energy performance ratings that are typically indicated by labels from the CSA or NFRC. 

The Canadian Standards Association (CSA) is a global organization that is based in Canada and develops standards in over 57 areas for a wide range of products including windows, doors, and skylights. Meanwhile, the National Fenestration Rating Council (NFRC) is a non-profit organization, based in the United States, that establishes standards specifically for windows, doors, and skylights. 

Additionally, you may also find labels from other organizations like Intertek, LabTest Certification Inc., and Quality Assurance International which all have similar ratings or metrics included in CSA’s labels. NFRC’s label, however, differs slightly from the rest. 

NFRC Label For Windows in Canada CSA Label for Windows in Canada
  • Solar Heat Gain Coefficient
  • U Value or U-Factor
  • Visible Transmittance
  • Air Leakage*
  • Solar Heat Gain Coefficient
  • U-Value or U-Factor
  • Visible Transmittance
  • Energy Rating*
Note: The R-Value** is an additional related metric that is not included on CSA’s/NFRC’s labels 
*Found on only one type of energy performance label

**Off the energy performance label but still related and used

As you will notice, U-Value is included in all energy performance labels on windows – along with solar heat gain coefficient (SHGC) and visible transmittance. However, other metrics like air leakage and energy rating, aren’t present on all labels. 

Though all energy performance ratings are helpful, it’s clear that U-value is a vital energy performance rating that is always included – and in the next section, you will understand why this is so. 

What Does A U-Value Rating on Windows Mean?

U-value is the rate by which ambient heat is transferred through a structure (e.g. windows, doors) from a warm area to a cold area. The lower the U-value, the better the window is able to provide good insulation. 

Therefore, having good U-value windows ensures that you will be able to…

  • Keep a steadier, cooler temperature using your ACU during the hot summer months, whilst using less energy
  • Keep a warmer temperature using your home’s heating during the cold winter season, whilst also using less energy.  

The following attributes of a window generally equate to a better (lower) U-value rating:

  • It has more than one pane (double-glazed, triple glazed, and so on)
  • The panes of glass are on a window spacer that keep them at an appropriate distance from each other
  • Argon or krypton (and not just ‘air’) is used to fill the in-between space between the glass panes
  • The frame of the window is made of high-quality vinyl (which has just as much insulating power as wood – but with less maintenance needed)

Energy-efficient vinyl windows used for a sitting room

What Is The Recommended U-Value Range for Windows

Whether you live in a cold or warm climate area, the lower the U-value of your window, the better. This ensures that the moment you close your windows, you can ensure that your heating or cooling system will need to work less because your window can insulate your interior space from any harsh temperatures outside. 

However, for colder climates, the lowest possible U-value for windows is best. This is because heating takes up more energy than cooling – so if you wish to save more in the long run with your investment in better windows, aim for a U-value rating of 0.17 to 0.39

What Other Energy Performance Metrics Are Related to U-Value?

Solar Heat Gain Coefficient (SHGC) 

This energy performance rating or metric is included in nearly all labels along with U-value and visible transmittance. This expresses the fraction of solar radiation (along with solar heat) that passes through a window. This is different from U-value because U-value measures the transfer rate of ambient heat, not direct solar heat. 

We discussed the importance of SHGC, along with recommended values of this metric, in our article, The Importance of SHGC Windows. Feel free to check that out for more in-depth information.  

Visible Transmittance 

This energy performance rating or metric is included in nearly all labels along with SHGC and U-value. Visible transmittance expresses the amount of visible light (and glare) that can pass through a window. 

Air Leakage 

Included mainly in NFRC labels, this measures the air movement that occurs through the window in situations wherein a difference in pressure is found on the two sides of the window. 

Energy Rating 

The energy rating serves to give a snapshot of three energy performance metrics put together: U-value, SHCG, and air leakage. So though some labels may not express air leakage, it can be taken into consideration through the energy rating. 


The R-value of a window is typically not included in labels but can be cited by contractors or the manufacturers of windows themselves. This metric expresses the amount of thermal resistance (i.e. the resistance to heat transfer.) Along with the U-value of a window, this metric gives further information about how well the window can insulate. 

The difference, however, is that R-value measures resistance to heat transfer while U-value measures the rate of heat transfer.

Therefore, a higher R-value and a lower U-value are indicative of better insulation.

Get High-Quality U-Value Windows For Your Property

This concludes our comprehensive guide on U-value windows. So now, the next time you go “window shopping,” you’ll be able to better understand the U-value/U-factor ratings on NFRC or CSA labels – along with the other related energy performance metrics. 
However, aside from superb energy performance ratings, you also need to make sure that your windows are durable, secure, and long-lasting. So get the best windows from trusted and acclaimed brands; browse through our list of trusted window companies today!

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