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Energy-Efficient Windows

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Tips on choosing energy-efficient styles and how to make your existing windows airtight.

In our Canadian climate, the thermal performance of windows is even more important than aesthetics. Find out the most efficient options whether you're improving existing windows or in the market for new ones.

In this article:
Types of windows
R-value
Air tightness
Solar transmission

Types of windows

  • Casement windows have side hinges, are operated by a crank and close with a compression weather-stripping that gets tightly squeezed when the window is locked. The compression seal renders this style of window one of the most airtight and resilient to heat loss.
  • Awning windows are similar to casement windows except they are hinged at the top and open out. They too use compression weather-stripping, which makes them typically quite airtight.
  • Double-hung windows have top and bottom sliding sashes. Double-hung windows are made with a type of weather-stripping that is less effective than casement or awning windows.
  • Single-hung windows resemble their double-hung cousins, but only one of the sashes operates. This type usually offers significantly better thermal performance than their double-hung counterparts.
  • Fixed or picture windows are the most energy-efficient since they don’t open and little, if any, air leaks through.

R-value

R-value is the measure of resistance to heat transfer through the glass. A window’s energy efficiency is largely determined by R-value and air leakage, while solar transmission also plays an important role.

When comparing R-values, make sure to check whether the manufacturer is listing the R-value of the whole window including the frame or if it only refers to the glass. Some manufacturers only report the “centre of glass” R-value which is typically higher than the “whole window” R-value. A double-paned, triple-paned or glazed window will have higher R-value than a single-paned window. The higher the R-value, the more energy-efficient the window will be.

R-value controls heat loss in winter and to some degree, heat gain in summer. To improve the R-value of existing windows, add storm windows or insulation.

Air tightness

Windows are also rated for air tightness, which is expressed as cubic feet of air leakage per minute per foot of crack length (cfm/ft). For casement and awning windows, look for an air leakage of 0.1 cfm/ft or lower. For double-hung windows, ratings of 0.2 cfm/ft or lower are best.

Air leakage can cause significant energy waste year-round and can be decreased with weather-stripping or caulking.

Solar transmission

Solar transmission refers to heat gain through a closed window. Unwanted solar transmission can be controlled in the summer by keeping shades drawn, while doing the opposite will allow heat to penetrate windows providing some warmth during cold weather months.

When researching new windows, keep in mind that frames are typically constructed of wood, vinyl or aluminum. Vinyl/wood hybrid frames are often insulated with foam, fibre, or gas-fill insulation and are generally the best for energy-efficiency.

Tip: To increase energy-efficiency on your existing windows, try repairing locks, replacing or repairing putty, installing storm windows, caulking around windows, or repairing broken or cracked glass.

 

Photographer: 

Rob Fiocca

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