As a single remodeling theme windows rank up there with the most renovated of all items in the home. This statistic has a lot to do with the fact that except for the front lawn, paint and siding on the outside of the home few features have the curb appeal of windows.
As a single remodeling theme windows rank up there with the most renovated of all items in the home. This statistic has a lot to do with the fact that except for the front lawn, paint and siding on the outside of the home few features have the curb appeal of windows.
Glass windows as we know them have been around in various shapes and colors since the Medieval ages but it was with the Industrial Revolution that made windows available for the average homeowner. Even the they were very expensive to buy, but to have a transparent shield against the elements in the 1830's was like owning the first colour television in your neighbourhood in the 1960's. It was definitely a status symbol.
Through the Looking Glass: 1 and 2 Pane
The early windows were one pane of glass that usually frosted up in the winter time when the weather was cold. However, in the 1800's, energy-efficiency was controlled by lighting fires, closing doors, putting on more clothes and, in many case, closing outside shutters. In those days, except in extreme cases, fuel was available fairly cheaply because wood could be found everywhere and almost every province had a coal mining industry. The loss of warmth and comfort from the single pane of glass was slowed with the addition of storm windows which could be put on in the fall and taken off in the spring.
When fuel consumption changed to oil and gas the price of these natural resources rivaled that of coal, and they burned cleaner than coal, especially gas. A new invention, double-paned glass had all but replaced the single-pane window with a storm window attachment making the semi-annual change of these windows redundant.
Windows Leak Energy
In the 1980's Canadian consumers began to realize that the price of natural gas was beginning to creep upward and that one of the major losses in home heating was through the windows. The average walls in a home had a R-value of 12 -15 - which means that this is the ratio that the wall resisted heat from leaving the home - and attics were R-30. However, even the best double-pane glass could only promise R-2, even with the dead air space between the panes.
Combination Windows
Using R-values for windows is not the the only way to measure their efficiency. There is also the U-value which is used to measure a combination of materials for heat loss. U-value is used to rate the conductivity of heat through a combination of building materials. For example, if R-values illustrate how much heat resists from passing through a material to the outside, U-values are the opposite. They measure how much the heat flows through the entire component. So if a high R-vale ( R-40) is a good indicator of energy efficiency a low U-value (U-.025) indicates the same.
The reason that this is important is because a window is a combination of R-values but the whole unit is measured in U-values. First, there are the two or three panes at 1 R-value each, then there is the thermal break between them which could have an R-value of 2 and, last, there is the gas between (argon or krypton) which has its own R-value based on quantity. So, the energy total of the three would be figured out as the U-value.
Improving Window Efficiency
- Triple Pane Windows: Adding another pane of glass decreases the U-value which decreases the amount of heat loss through the window. It is another obstacle that the heat has to leap before getting out.
- Argon/Krypton Gas: Inherent in the air spaces between panes in any window system is “convection.†This is the movement of air is caused by the forces of cold on the outside and warmth on the inside. The hot air in the top of the window space cools and descend and this convergence of forces leads to currents of air which move in an elongated circle as. Argon and krypton are heavy gases which slow down this convection and therefore slow down the heat loss.
- Window Coatings: Another way to increase heat inside the home in winter is through low-emissivity and reflective coatings which are so thin that you can't see them with the naked eye. These coatings reflect the heat back into the home. Any low-e coating is like having another pane of glass on your window.

In hotter climates the reflective material is positioned so that long radiation waves are deflected and prevents the heat from overdriving the HVAC system.
- Solar Gain: Another way windows are judged is through their Solar Heat Gain Coefficient (SHG) rating which is the amount of solar energy that passes through. The aim of building designers is to maximize the amount of solar heat gain in the winter time to help with heat costs and deflect the sun's rays in the summer to keep the cost of air conditioning down.
Window Placement for Energy Savings
For the Canadian climate - which is extreme in many areas of the country - windows have to be able to be a combination of heat retention and deflection. But this should not always be up to the window manufacturer. The number of windows and their placement should be considered, as well.
For example, windows placed facing southwest will take in the long winter sun's rays directly but will not be in direct line with the hot, August sun. At this time the sun will be too high to catch the windows dead -on. And if the windows are not correctly placed the homeowner can use awnings to deflect the summer sun.
Posted by: TrustedProsSuggested Reading For You
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