Energy-Efficient Windows is a Hot Topic


In most areas of Canada having energy-efficient windows is not only important in saving energy in the home it also mandated in the building codes. In Nova Scotia, the minimum requirement for windows in new home construction is "Low E and Argon," meaning that the panes of glass have an, invisible reflective coating to keep heat inside the home and the space between the panes is filled with a heavy, argon gas.

The "McMansion" is Dead

During the building booms of the 1990's and the first eight years of the New Millennium the dream of many people who wanted a new home constructed was to build it bigger. This meant that the large, 3,000 square-foot dream home of the 1970's had grown to 5,000 square feet or more. Many of these homes were so large they needed two furnaces to provide heat.

Skyrocketing energy costs during the last five years slowed this trend and then the economic meltdown in the United States sobered up the new home building and renovation industries in Canada. People and governments were coming to grips with the fact that the days of cheap energy were over. Homes that were once heated for $2,000 a year in 1990 were now seeing power and fuel bills surpass the $5,000 mark. This hike in energy costs could be handled in the short term but months have now rolled into years and, with paychecks being frozen or lightened, homeowners began realizing that smart energy savings was the only path.

Glass and Metal

One of the biggest sucks in energy is the window system of a home. A normal home built in the 1960's with 4" walls has an R-value of 15. The R-value is the resistance of a material to heat flow and the higher the R-value the better the blockage of thermal energy across the surface. Here is a breakdown of windows across the spectrum of thermal efficiency:

  • Single pane = R 1
  • Dual pane = R 2
  • Dual pane with Low E only = R 3
  • Dual pane with Low-E and Argon gas filling = R 4
  • Triple pane with Low-E and Argon gas filling = R 6

It is plain to see that the only job that the old single pane-glass performed was to keep out wind and the elements. Like sheet metal these surfaces literally vacuumed the heat from any room. In fact, the old movies showed beautiful frosting on the interior of the glass as water vapour froze.

Up until just a couple of years ago the strategy for insulating against the cold was to provide a thermal rating of at least R-20 in the walls and R-40 in the attic. During the past few years the requirement for the building of new homes has pushed these figures much higher depending on what part of the country the home is being built.

Dual Panes Are Also Losing Heat

There are three ways that dual pane-glass are not good insulators:

1. Solid glass conducts the cold: Unlike foam or even plastic glass conducts heat and cold almost as well as metal. One of the laws of thermodynamics states that heat does not want to exist naturally and so is drawn to the cold. This is why a home can have cold spots near windows because and heat is neutralized by the cold glass surface.

2. Ordinary dual-paned glass is not a good insulator: The dead air area between the glass panes offers some insulation but only by a margin of R-1, making a dual-pane window R-2 as compared with R-15 to R-24 for the wall. This is because of another property of thermodynamics called convection. Like a miniature weather system the cold outer pane and warmer inner glass causes the air in the space between them to circulate in a convection current. This action helps the movement of warm air from the home to the cold outside.

3. Window spacers in most windows are metal: The panes of glass are held in place by spacers and most companies use aluminum, as it is light and strong. However, aluminum speeds up the transference of cold even with foam-filled vinyl sashes.

Window Manufacturers Overcome Deficiencies

The companies that make windows have made great strides in the design that make them more efficient.

1. Low Emissivity Coatings: Heat can be retained in a home by reflecting it away from the glass and back into the home. A protective, transparent, metallic coating on the glass not only performs this job but in the summer can prevent excess heat from entering the home.

2. Gas-Filled Spaces: Window manufacturers are also filling the air space between the panes with heavy gases like argon, krypton and xenon. Not only are these gases not as conductive as plain air or nitrogen they slow or stop the convection currents that promote heat loss.

3. Foam-Plastic Spacers: Conduction of cold through the frame causes condensation and mould and promotes seal failure. Having a foam-plastic spacer stops thermal transfer and also moves with the panes during expansion and contraction or heavy pressure from winds.

4. Vinyl Window Frames

Wood and metal still have a market in high-end homes where aesthetics are very important. However, the positive attributes of vinyl window construction makes this type of material both cost-effective and energy-efficient.

For more information on replacing your present windows consult our Contractor Directory or simply post your project online.

Posted by: Kim Kinrade
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