Clera Windows + Doors Windows

What is R-Value and why is it important?

If you’re like most new homeowners, you turn to the internet to research new construction ideas you have for your home before you move forward with a project. Take replacement windows for example, you probably never needed to consider everything there is to know about windows until it was time to replace your own. And that’s completely fine because high-quality windows should last you many years, it’s not likely that most people are experts at buying new windows as they would be price matching at the supermarket.

During your research of replacement windows, you probably came across some unfamiliar terms that sound like it would be an important deciding factor, but you’re still unsure exactly what it means. Terms like R-value and U-value is something you may hear often in this industry after all, what matters most to a lot of homeowners besides quality, safety, and aesthetic is energy-efficiency.

So, what is R-Value and why is it important to know about when buying replacement windows? Here’s the answer: R-value is the unit of measure that is used to describe the thermal resistance of an object such as, a window. In other words, it tells how well the window will work to insulate your home. The higher the R-value number of a material, the better its insulating properties and the slower the heat flows through it either from a warm, heated space to cold outside temperatures of from a hot exterior to a cool, air conditioned space. Basically, It is used to compare the insulating values of different products, like insulation or on windows. Which is why It is important in choosing a replacement window because the higher the R-Value the less thermal transfer will occur.

You may also come across a term, U-value which is the inverse of R-value. U-value measures how well building materials conduct heat. A lower U-value indicates a more energy efficient window and that it has greater insulating qualities and resistance to heat flow. When choosing replacement windows for your home, choosing a window type that has a lower U-value such as a U value of 2 would be particularly beneficial during cold weather months because you wouldn’t have to compensate for the heat loss through your windows by running your furnace longer in order to keep your home warm.

What you’ll notice while shopping for new windows is that most window manufacturers have started developing energy efficient windows that are labeled with an R-value rating. It has become easier for the consumer to grasp the concept when making a valid comparison while selecting between different window materials and designs. For example an R6 window is better that an R5 window and a U-value of 2 indicates that window has excellent insulating properties. To put it nice and simple, U-value refers to the rate of heat loss through a window, R-value refers to the window’s ability to retain heat.

By now the volume of information can be overwhelming, but to make comparison shopping a little easier for you, we compiled a brief overview of the main components you should be looking at in addition to R and U values, in order to determine the energy-efficient rating of a window:


Energy Star is a certification system used only within Canada and the United States to easily identify energy-efficient products. Here’s what most people don’t realize, not all Energy-Star products offer the same level of energy-efficiency. The Energy-Star rating simply means the product has met or exceeded the requirements and standards of the Energy-Star certification program. Also, these standards are not fixated because as technology continues to evolve and change, so will the standards. So, when considering a products Energy-Star rating, it’s important to ensure you’re referring to the latest figures.


When you see a products visible transmittance rating (VT) it will be indicated as a percentage. What it means is the amount of visible light that can be passed through the window. A lower VT means that less light will be able to enter the home through the window. You’ll see this more with Low-E glass windows. Higher quality Low-E windows will offer the most comfortable balance of light while still controlling the amount of heat that’s gained. It’s perfect for letting the sun spill over the room with overheating during the day.


The amount of air that passes through gaps in a window can be measured and this figure is referred to as air leakage. Pretty self explanatory, a higher rate of air leakage would show that the window is more prone to heat loss and gain which is not good for energy-efficiency. Air leakage can be a result of a poor quality window or poor installation particularly around the window frame.


This figure is pretty neat and will show you the overall energy-efficiency score of a window. It will incorporate all the components mentioned in this article. It provides consumers a more convenient way to compare products. The standards for energy ratings vary according to climate zone. To earn the ENERGY STAR label in Canada, a window must have a minimum energy rating of 25 in zone 1, 29 in zone 2 and 34 in zone 3.

Whenever you’re shopping for new replacement windows, there’s no harm in getting the helpful advice from the professionals. Get connected with a specialist at Clera Windows and Doors and get more information for your home. We’ll be happy to give you more insight on whether or not your current door frame system will be compatible with you brand new replacement door for many years to come. As a family run company since 1978, you can be assured that we understand and appreciate the importance of any home renovation project to your family. We’re in the business of providing comfort and security for households across Canada, and we couldn’t be more grateful for all the homes and families that have entrusted us with such an important decision to improve their home’s functionality and security. All of our fenestration installation technicians are rated by the Canadian Standards Association and our products are all ENERGYSTAR rated as well, so you know our work can be trusted. We’ve also taken home the “Top Choice Award” and are so confident in our craftsmanship that we include a written, lifetime factory warranty on our products. What this means for you is that you won’t have to buy another pesky replacement part again. Contact Clera Window and Doors today to find a specialist in your area and to book a free consultation.