Industry reports have shown that even when a house is fully insulated – walls, floor and ceiling, that up to 48% of the heat loss occurs through single glazed windows.
Double glazing is most commonly produced as a factory-sealed unit where two panes of glass are separated by a still air layer of between six to 20 mm. These are then fitted into window frames, which are usually made wider to accommodate the double-glazed unit. Factory made units contain dry air between the layers of glass, a desiccant (silica gel) to absorb any moisture likely to cause condensation and are usually double sealed.
Another method of reducing heat loss through glazing is to use low emittance (Low-E) glass. This glass has a special coating which reflects radiant heat back into the room. The coating is located on the glass inside the air space, and reduces transmission of radiant heat from the warmer glass to the colder glass. Low-E glass is generally only used in conjunction with double glazing. Depending on the direction the coating is facing, Low-E glass can be used to reduce either heat loss from inside a building or heat gain from outside (in hot climates). The use of Low-E glass to control heat gain is not recommended for Victorian conditions as it also reduces the amount of solar gain in winter.
The material of the window frame can affect overall window performance. Materials with high heat conductance cause more rapid heat loss from the heated interior in winter and higher heat gain in summer. PVC and timber frames generally perform better than metal frames, unless metal frames have thermal breaks to decrease conductance across them.
All Smarterhaus homes are fitted with double glazed windows.
For more detailed information about window energy efficiency check out www.sustainability.vic.gov.au.
Tags: energy efficiency rating