Homeowners and builders have incorporated energy efficiency into their purchases for decades. We know that more insulation is better and the right ventilation makes heating and cooling perform better. Windows are an important part of the home insulation/ventilation system.
Each part of the window helps or hinders energy efficiency, depending on how well it is made or how deteriorated it is over time. The sills and frames must fit tightly and have no breaks; the stiles and rails must hold the glass firmly. However, the most important area of insulation is the glass itself.
The latest improvement in home windows is double-glazing. Each pane consists of two pieces of glass with a space in between. The air is removed between these two, creating a vacuum. The transfer of heat and cold is reduced because neither travels well through a vacuum.
When it comes to building or replacing windows, cost is on top of the list for many people. Double-glazed windows are decidedly more expensive than single-pane windows. The savings in double-glazed windows is in energy use over time. Regulations require that each window be rated for its energy coefficient by a national council that determines how much heat is lost in winter and allowed in in summer.
One often overlooked fact about windows is that double-glazed products reduce noise from the outside due to the same dead air space in between the panes, which tends to deaden noise. If you live where noise can be a problem, this is one more reason to choose double glazing. When purchasing replacement windows, the homeowner should check the availability of tax credits for highly efficient (double-glazed) products. The federal government has several energy related credits, but they change from tax year to tax year.
One caution about double glazed windows: be sure to get a guarantee about the quality of the seals of the glass pieces. If the seals are poor, the space between the glass panes can cloud, allow water to collect or discolor. These defects are very difficult to fix, often requiring all-new windows to be installed. Make sure the guarantee includes the energy-saving gaps in the glazing.