Step 5

How Important Is Window Insulation?

ENERGY STAR®, R value, U value, Solar Heat Gain Coefficient… insulation is essential, because it ensures the best energy performance. It helps reduce energy consumption (and energy bills), improves air quality and increases comfort on a daily basis.

Here are some tips to help you get the appropriate insulation:

Energy efficiency is expressed in R or U values in the United States, whereas in Canada, it is expressed in R, U or ER values.

R Value

The R value is the resistance of a given material to thermal transmission. The higher it is, the better the insulation. Specialists will often refer to the R value, and it’s definitely an important number. Please note that a typical home wall gets an R-25 rating, whereas an excellent window gets an R-5. This is why the R value should not be your sole criterion.

U Value

The U value indicates the heat transfer rate, which is calculated by inverting the R value (1/R). The lower it is, the better the insulation.

ER Coefficient

The Energy Rating (ER) calculation is based on the balance between heat transfer (U factor or U value), solar gain and air leakage. The higher the ER, the better the energy performance.

ENERGY STAR® Certification

This is a voluntary certification obtained by manufacturers, which means that there are products on the market that offer excellent energy performance, but aren’t ENERGY STAR® certified. However, the ENERGY STAR® certification is proof that a product is eco-energetic and that its insulation quality has been attested by an independent expert!

If you would like more information on this certification, please visit the ENERGY STAR in Canada site or ENERGY (United States).

To understand how to interpret ENERGY STAR® results, read the Expert Advice section.

Although this information is important, it’s also important to look at profile design, glazing, etc. These elements will also influence the long-term efficiency of a window.


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