Energy usage is often determined by how much heat is transferred to and from a building envelope via inadequate insulation and air leaks around doors and windows. Adding insulation to the attic and walls is good, but double-glazed window and door glass contributes greatly to the reduction in heat transfer.

An insulated glass unit is fabricated from two pieces of glass, an aluminium or vinyl separator filled with a desiccant and a sealant that holds it all together. This double-glazed unit may be glazed into doors, windows, skylights and other fenestration products. The energy loss through conduction is reduced by as much as seventy percent, depending upon the type of glass used and the depth of the dead-air-space between the pieces of glass. As well standard annealed glass, there is also low-emissivity glass that uses a microscopic metallic film to reflect heat either back to the inside or outside, depending on which surface the film is applied to. Inert gasses may be added to the unit for further reduction of heat transfer.

The energy transfer ratings of glass are as follows: Single glazing, 5.0 Double glazing, 3.0 Triple glazing, 2.2 Double glazing with Low E glass, 1.7 Double glazing with Low E and Argon, 1.2 This means that the heat transfer of the glazing in windows and doors may be reduced by more than seventy percent.

Leaky windows and doors are another contributor to energy transfer. Modern advances in weathering technology; weather-stripping, tighter manufacturing tolerances, new materials and improved technology; have produced window frames that all but eliminate heat transfer around sashes and through gaps in frames. Coupled with double-glazing, window units are now quite energy efficient.

Modern window designs allow for glazing for up to one inch in depth, so coupled with the tighter seal around sashes, these windows greatly reduce energy loss, enough so that they will usually pay for themselves in three to five years by the reduction in energy bills for both heating and cooling. When new windows are installed in a properly prepared opening, modern caulks and flexible sealants are used, thus the entire building envelope is tighter with less drafts and energy loss.

In addition to the benefit of lower energy costs, the new windows produce little or no draft. Also, the outside noises are reduced by up to forty percent. New window in a residence or commercial building are energy efficient, better for one?s health and contribute greatly to the quietness of the building interior.

Modern window frame material also contributes to the energy use reduction by diminishing the heat transfer through the frame material as well as in the better weather-stripping. Polyvinyl fluoride, PVC, is often used in residential windows because of the non-conductive nature of PVC. Where aluminium commercial windows are used, they have a non-conductive material poured into a pocket in extrusions, which is then ?debridged,? the conductive aluminium on the bottom of the pocket is removed.

It is a wise choice to select double glazed window units when upgrading any building for both aesthetic and energy related reasons. The new windows add to the appearance and value of the structure and provide a healthy, quiet, energy efficient environment for homes and offices.