Blog > Category Post > Updated: 2017-Dec-22

What is a window U-factor

The lower the U-value, the better the window is at keeping the heat in during the winter and the better it insulates
In Ottawa, our windows lose heat to the outside during the colder months and gain heat from the outside during the warmer months. U-factors allow consumers to compare the insulating properties of different window products in order to optimize home comfort.

Measuring non-solar heat that escapes through a window out of a home

The U-factor (U-value) also known as the overall coefficient of heat transfer is a measurement of thermal conductivity (heat gain or loss) through a window due to the difference between indoor and outdoor air temperatures. U-value ratings generally range from 0.2 and 1.25.

For windows, the frame and the edge of the glass usually have higher U-values than the centre of the glass. So when looking at windows you need to know the U-value for the entire window (frame + glass).

Most manufacturers give U-values for the whole window, but some do not. Energy Star window U-factors measure the window performance as a whole.

Energy costs from non-solar heat flow are greater when heating the home than it is from cooling the home.

U-factor summary for Ottawa:

  • The smaller the U-value, the better the insulating properties of a window which helps keep home heating inside the home during the winter.

Need help deciding what U-factor 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.