U-Value (and R-Value) for Window Replacements

Windows are an integral part of any home's interior and exterior design. They also serve as a thin barrier between the indoor and outdoor environment, making them prone to heat and airflow. This can lead to energy wastage and make the home atmosphere reactive to weather changes. To keep your home comfortable and energy-efficient, it is crucial to consider replacing your windows with energy-efficient ones.

At Good Home Insulation, we offer top-notch window replacement services that will keep you comfortable and save you money all year round. Say goodbye to drafty, outdated windows and hello to energy-efficient, stylish ones.

How Window Insulation is Measured

Energy-efficient windows should block the sun's heat and UV rays during summer while keeping the heat inside during winter.

Two metrics are commonly used in the window industry to measure heat flow and efficiency: U-value and R-value. These metrics are the inverse of each other. The R-value measures heat resistance and material effectiveness, while the U-value calculates the conduction properties of various window materials. 

  • R-value:

The R-value measures the performance of a specific window material, such as insulation, in reducing the transfer of heat. The R-value is essential in educating users about a window's ability to block air flow in and out. It depends on the number of panes, the frame type, and the window size. The more panes and space between them, the higher the R-value. Low-E glass, which has a coated finish that reflects heat while allowing natural light into spaces, can further increase the R-value.

  • U-value: 

On the other hand, the U-value measures the conduction properties of various window materials. It specifies energy efficiency, measures insulating ability, and is an indicator of heat transfer, airflow, and radiated or reflected heat. The U-value is used by the National Fenestration Rating Council (NFRC) to certify energy-efficient windows and provide information to consumers about their performance.

Indicates Energy EfficiencyYesYes
Measure of InsulationYesYes
Based on Specific MaterialYesYes
Based on Multiple FactorsYesNo
Indicates Heat TransferYesNo
Indicates Heat ResistanceYesYes
Measures AirflowYesNo
Measures Reflected HeatYesNo
Lower Number is BetterYesNo
Higher Number is BetterYesYes
On NFRC LabelYesNo

What Are Good R-Values & U-Values?

For replacement windows, it is best to look for high R-values and low U-values, which together indicate that there are neither any major air leaks nor that the windows are effectively insulating your home. 

According to energy.gov:

A good R-value range: Greater than R-5.

A good U-value range: 0.20 – 1.20 according to energy.gov.


We know that the R-value measures heat resistance, but that implies more than is obvious at first glance. The measure of heat resistance of the glass implies a measure of

Glass energy efficiency

Glass insulating ability

The R-value will depend on:

  • The number of panes of glass
  • The type of frame
  • The size of the window

Here’s a representation of what R-values could look like:

Type of PaneWinterSummer
Single Pane.9.96
Double Pane with .25” air space1.721.64
Double Pane with .5” air space2.041.78
Triple Pane with .25” air space2.562.27
Triple Pane with .5 air space3.222.56

At Good Home Insulation, we offer windows in four substrates: clad wood, vinyl, aluminum, and fiberglass. Each of these has its own R and U-value. To determine the optimal R and U-values for your replacement windows, explore our window offerings and get in touch with any questions you may have. Replacing your windows with energy-efficient ones is not an expense but an investment in your property, providing upgraded curb appeal and energy efficiency.



Good Home Insulation

We’re committed to saving you money and safely keeping your family comfortable all seasons of the year.

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