U value vs R-value: Comparison & Relevance

You often hear these terms, but do you really understand what they mean? It’s essential to take the time to understand these two key insulation components and how they relate to your home’s heating and cooling.

U-value and R-value both quantify energy efficiency. The U-value measures heat transfer (heat gain or loss) through the glass, whereas R-value measures heat resistance. Or the insulating properties of a material to reduce heat transfer.

The U-value and R-value are crucial to an energy-efficient home, but in different ways. To help you decide which one you should pay more attention to, here’s an overview of both U-value vs. R-value:

What is U-value?

U-value measures the conduction properties of a building material such as windows, roofing, flooring, or bricks, but it is not a rating of the material. Generally, it is a crucial determinant of the energy efficiency of window units in a building.

A scientific calculation method is used to measure U-values. The results are presented in watts per square meter per kelvin (W/m²K). It is a measure of

• Thermal resistance
• Insulating capacity
• Heat transfer levels
• Airflow

Is a higher U-value better or worse?

The U-value measures how well a building material or other surface prevents heat from passing through. The lower U-value means it is better at insulating. Conversely, the higher the U-value, the more heat can pass through.

For example, a single-glazed window has an average U-value of 5.0, while a double-glazed window has an average U-value of 1.6. You can see that single-glazed would be worse at insulating than double-glazed windows because it allows almost three times as much heat to pass through.

What is R-value?

R-value is based on the material’s capacity to lessen heat transfer. In other words, it measures the insulating efficiency of a material. It shows how well a material can resist heat flow at a certain thickness.

R-values are presented in meters squared Kelvin per Watt (m2K/W). It depends on the thickness and density of a material.

R-value represents:

• Energy efficiency
• Insulating power
• Heat resistance

Is a higher R-value better insulation?

A higher R-value means higher resistance, so a material with a higher R-value is better at insulation. Also, different thicknesses of the same material have different R-values because R-value increases as the thickness of the material increases. For example, a one-inch fiberglass batt has an R-value of 3.7, while a two-inch one has a higher R-value of 7.4 and will provide better insulation.

U-value vs R-value – A comparison

Comparing the properties of both values will help you understand the purpose of these energy efficiency measurements in a better way.

Similarities

Many similarities between these two values can lead you to confuse one with the other. U-values and R-values are similar in the sense that:

• They measure energy efficiency based on the insulation capacity of materials.
• Both represent measurements’ however, these measurements are of different types.
• They both depend on the thickness of the insulation material.

Differences

• The U-value is a heat transfer indicator; R-value is a heat resistance indicator
• The U-value measures airflow as well as radiated or reflected heat, while R-value doesn’t.
• R-value is based on a material’s particular feature, whereas U-value is calculated scientifically.
• National Fenestration Rating Council (NFRC) is a public service organization that provides information for comparing the energy performance of building components. It includes U-value but not R-value certification in its labeling.

Let’s look at the summary of the similarities and differences between the U-value and R-value in the following table:

How are U-value and R-value linked?

U-value and R-value have a close relationship. In mathematical terms, they are reciprocals or inverses of one another. To convert R-value to U-value, you must divide 1 by the R-value and vice versa.

So, if you have any of the two values, you can find the other.

To get R-value: divide 1 by U-value. If U-value = 0.20, 1 ÷ 0.20 = 5

To get the U-value: Divide 1 by R-value. If R-value = 2.7, 1 ÷ 2.7 = 0.37

Although a home’s U-value and R-value are two different things, they are both used to measure the thermal efficiency of windows. A home’s U-value is how well it prevents heat from escaping, and its R-value measures how well it resists the inward flow of cold air. The lower the U-value or, the higher the R-value, the more efficient your window is at preventing heat loss or cold air intrusion.

Why do I need to know about U-values and R-values?

During home construction, you want to ensure that all standards have been met to make a home energy-efficient to the optimal level. By knowing the R-values of the insulation materials used in the construction, you can predict if the materials can successfully prevent heat transmission between the interior and exterior of the home.

The knowledge about R-values can help you compare different insulation materials. It means you can choose the best insulation material with a high R-value and less thickness according to the insulation needs of the area.

Similarly, insulating the building properly with low U-values ensures that your heating bills will not skyrocket, particularly in winter. It is because lower U-values of the insulation material mean that the home will be at an optimal temperature, mostly without using extra energy to keep your home’s interior warm.

How Can I improve my home’s U-value?

By improving the U-value of your home, you can save on energy bills. An unfilled cavity wall has a high U-value and may be responsible for substantial heat loss from your home. You can decrease the U-value by adding insulation to your exterior walls and reducing heat loss.

Another way to improve your home’s U-value is by swapping single-glazed windows with double-glazed or triple-glazed ones. However, windows with a high U-value can be more expensive than those with a low U-value. In most cases, that cost may be worth it for the increased comfort provided by better insulation.

You can also improve the U-value of your home’s windows by

• Using a noble gas, e.g., argon, in the cavity between glass panes
• Changing the cavity size to ½” (suitable for both air and a noble gas) between the window’s glass panes
• Using warm-edge window spacers for effective thermal barrier
• Using Low-E window coating to reflect long-wave infrared rays

Does the R-value make a difference in the energy efficiency of windows?

Where U-value only concerns the glass of the window, R-value considers the performance of every insulation material used in the installation of windows. These materials include caulking or any other sealant used, insulation in the space between the window and the wall, and any edges, trims, or other components related to the windows.

Conclusion

R-value and U-value are both vital when considering the insulation needs of any building. Try to choose the most suitable insulations with high R-values and low U-values. Hence, you have a comfortable living environment in your home without spending a fortune on heating or electricity bills.

Charles John

A novice DIYer who learns about home ventilation. I am a mechanical engineer and have a basic knowledge of HVAC systems but I learn continuously to make myself the best blogger in that space.