We often discuss energy efficiency on our blog and for good reason! By investing in energy efficient windows and doors, you can reduce energy waste, lower your utility bills and create a more comfortable living environment. You can also benefit from government green energy rebates. Furthermore, the better you understand energy efficiency, the more selective you will be when buying new windows. One of the most important measures of glass window efficiency is the U-factor. In this blog, we explain what a window’s U-factor is, why it matters and design elements that can improve the U-factor.

What is Window U-Factor?

The U-factor is an indicator that determines the amount of heat escaping from a house through a glazed window or door unit. It is an important indicator of the extent to which window units prevent heat loss generated by objects in the home (e.g. HVAC units). It is also one of the most important indicators used by the wider fenestration industry to measure energy efficiency.

U-Factor as a Comparative Performance Rating

The U-Factor is one of four key energy performance ratings used by the National Fenestration Rating Council (NFRC), an independent third-party organization that provides objective testing and certification for glass windows, doors and skylights Other organizations, such as ENERGY STAR®, also use them The four key rating criteria are:

  1. U-Factor
  2. Solar Heat Gain Coefficient
  3. Visible Transmittance
  4. Air Leakage

By using these consistent evaluation criteria, NFRC makes it easier for homeowners to make sensible decisions about window replacement. This is because all windows tested by NFRC are based on the same consistent performance criteria.

What is a Good Window U-Factor?

The lower the U-factor, the better the window is at preventing heat loss; NRFCs range from 0.20 to 1.20. In cold climates, installing windows with U-factors between 0.20 and 0.40 can be of great benefit in improving the energy efficiency of your home.

U-Factor and Insulation

The U-factor is a good indicator of how well windows and doors insulate a home, and when measuring a window’s U-factor, the NFRC considers the performance of the entire unit rather than just the glass (or glazing) of the window. A low U-factor means that all components of the window unit are working together to improve the insulation of the home.

The Difference Between U-Factor and R-Value

If you are renovating a house, you may have seen the term R-Value – R-Value and U-Factor are related to heat and insulation, but they are distinctly different.


  • Measures how well different building materials resist heat the flow of heat
  • The higher the number, the better the material’s thermal resistance
  • Commonly used to gauge the insulating properties of wall and flooring materials


  • Measures the rate of heat flow or heat loss through a window unit
  • The lower the number, the less heat loss occurs through the window unit

5 Window Design Elements Can Help Improve U-Factor

The NFRC takes into account the performance of the entire window unit when calculating the U-factor. Therefore, it is important to understand which window design elements can reduce heat loss. Keeping these design elements in mind when purchasing new replacement windows will help you ask the right questions during the buying process!

1. Vinyl Window Frames

Vinyl is a very energy efficient material due to its low thermal conductivity. This means that heat and cold cannot easily pass through vinyl. The higher the thermal efficiency of the window frame, the better the window insulation. In addition, vinyl frames have welded corners that help them to be waterproof. Unfortunately, there are still some disadvantages to using vinyl frames.

The Northtechwindows by Canglow™ Difference: Vinyl’s low thermal conductivity aside, it’s also very susceptible to wear and tear as well as expansion and contraction in the heat of Canadian summers and the bitter cold of the winters. To counteract this, we reinforce our vinyl frames with anodized aluminum and galvanized steel. That way, you get strength, durability, and efficiency in equal measure.

2. Gas Fills

Gas filling is an important step in creating insulating glass units and reducing the U-factor of windows. Manufacturers fill the space between the glass panes (called glazing) with krypton, argon or xenon gas. These heavier, nobler gases are preferable to filling the unit with air as they can better block the transfer of heat through the window.

Most IGUs on the market are spaced 1.5 to 3.4 inches apart. Our innovative approach to window hardware design has allowed us to increase this spacing by 1 inch. This means we can fill the IGUs with 25% to 50% more gas. More gas provides more effective insulation when it is really needed.

3. Low-E Coatings

Low-E coatings are transparent, very thin, lightly colored coatings added to window glass. It helps to control or regulate solar radiation passing through the window glass. When controlling heat, Low-E helps reflect the following types of radiation

  • Shortwave Infrared Radiation: Heat that streams through a window directly from the sun.
  • Longwave Infrared Radiation: Heat absorbed and emitted from other objects, such as objects inside the home

It is important to customize Low-E coatings according to climate, geographical location and the structure of the house. In general, there are two types of Low-E coatings. Solar Control Low-E actively reflects the sun’s heat through the outward-facing window glass, while Passive Low-E reflects indoor heat through the inward-facing window glass.

If you think of a standard double-glazed window (a window unit containing two panes of glass), there are four glass surfaces:

  • #1: The outside-facing surface of the exterior pane
  • #2: The inside-facing surface of the exterior pane
  • #3: The outside-facing surface of the interior pane
  • #4: The inside-facing surface of the interior pane

Windows that have Passive low-E coatings added on the 3rd and 4th surfaces (the ones closer to the interior of the home) can improve U-Factor:

  • It helps homes contain heat by reflecting long and shortwave infrared radiation (or heat) back into the home.
  • In colder climates, passive low-E allows homeowners to take full advantage of solar heat gain and relieve the burden placed on artificial heat sources.

4. Warm Edge Spacers

Warm edge spacers are an important component of insulating glass units (IGUs). The term ‘warm edge’ comes from the formability of the IGU, which expands and contracts with the movement of the IGU, preventing gas leakage. This airtight seal also prevents heat loss, air leakage and condensation inside the window glass – the IGU is an important line of defense in maintaining the window’s airtightness, insulation and energy efficiency in the long term.

5. Thermal Blackout Blinds

Using thermal blinds can significantly improve the thermal insulation of windows. In winter, these blinds can reduce electricity bills and prevent heat loss by preventing comfortably warmed air from escaping.

The Northtechwindows by Canglow™ Difference:  Our built-in, fully retractable insect screens, solar shades, and blackout blinds give you complete control over when, where, and to what extent your screens and blinds are in use.

Want to Learn More About Installing High-Performance Windows?

While performance such as window U-factors and third-party measurement standards are important, what matters most is that the windows deliver exactly the performance your home needs. That’s why we develop our own glazing units to meet the solar and energy control needs of different regions and climates. We also maximize the performance of our windows to suit your preferences, the climate and the structure of your home.

Looking for more information about U-Factors or window replacement in general? Contact us today and schedule a free consultation with one of our representatives!

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