Window Energy Efficiency
PVC-U is the dominant frame material in the domestic home improvement market and the insulating glass unit (IGU) is required to attain an 'A', 'B' or 'C' window energy rating (WER) banding.
There are three elements to an insulating glass unit:
- the glass
- the spacer bar
- the cavity
Each of these has been subject to performance improvement over the years.
THE GLASS - Low emissivity (low 'e') can be used for the inner pane which filters some long wave radiation from sunlight - cooling in summer - while reflecting short wave radiation from heating systems to keep heat in during the winter. For the outer pane, low iron glass is optically clearer which helps to harness solar gain.
THE SPACER BAR - Warm edge technology for spacer bars dramatically reduces heat transfer at the extremities of the IGU
THE CAVITY - filling the cavity with gas increases the insulation properties
According to Richard Bate, Technical Director of Build Check "As a general rule of thumb, for most PVC-U windows, a gas filled IGU with low 'e' glass will reach a 'C' band. Add warm edge spacer to move to a 'B' and low iron glass to hit an 'A'.
Source: Glass & Glazing Products - May 2010