Understanding the R-value

Measuring heat flow into or out of a house

The R-factor actually simplifies some of the window spec confusion. Making it easier for architecturally minded people to calculate required wall and window specifications in the same measurement units in order to meet required Canadian and Ontario building code standards. It also makes it simpler for the average window customer.

The R-value, also known as the inverse of the U-value (more familiar to standard window specifications) is a rating of thermal resistance or the ability of heat to transfer from hot to cold, through a material. Simply put, for windows it is a rating measurement of the overall insulating value of a window.

R-values are most commonly associated with wall insulation and if you think of it in that respect, better-insulated windows (higher R-values) slow the rate of heat transfer (heat resistance) through the window.

The R-value is actually calculated from the U-value, by dividing the U-value into 1, (R-value = 1/U-value).

Example: U-value of .31 (imp.) = 1/.31= an R-value of 3.225 (imp.)

The higher the R-value, the greater the resistance to heat and the better the insulating properties. In the winter heat stays in and in the summer heat stays out.

Windows with higher R-values translate into:

1. Lower energy consumption in the home
2. Reduced solar heat gain
3. Consistent temperature uniformity and increased home comfort

R-value Summary for Ottawa

• R-value - Overall insulative value - the higher the R-value the better the window performs as an insulator.
• U-value - Amount of heat that escapes through a window - The lower the U-value the better the insulating properties of a window

Need help deciding what R-value is right for your rooms, leave the guessing out of it, talk to your local window specialist. They’ll help you find the perfect window, that will maximize your home comfort and minimize your energy costs.