Low-E glass has a microscopically thin metallic coating — typically silver or tin oxide — deposited on the glass surface. The coating reflects long-wave infrared radiation (heat) while allowing visible light through.
The result: in winter, radiant heat from inside your home is reflected back inward rather than conducted through the glass. In summer, solar heat is reflected outward before it enters the room.
The U-Value Difference
U-value measures heat loss through a material. Lower is better.
| Glass specification | U-value (W/m²K) |
|---|---|
| Single pane (4mm clear) | 5.6 – 5.8 |
| Standard double glazing (air fill) | 2.7 – 2.9 |
| Hard-coat Low-E + air fill | 1.8 – 2.0 |
| Soft-coat Low-E + argon fill | 1.4 – 1.6 |
Melbourne's climate requires heating for roughly four months of the year and cooling for two to three. Both are meaningfully affected by U-value. The improvement from standard double glazing to Low-E is real and measurable in energy bills.
Hard-Coat vs Soft-Coat Low-E
Hard-coat (pyrolytic) Low-E is applied during the float glass manufacturing process, baked onto the surface at high temperature. It is durable, scratch-resistant, and can be cut and handled like standard glass. It performs well but not to the level of soft-coat.
Soft-coat (magnetron sputtered) Low-E is applied post-manufacture in a vacuum chamber. It performs significantly better (lower emissivity values), but is fragile and oxidises if exposed to air or moisture. It must be installed facing inward into the IGU cavity — never on an exposed surface.
For retrofit double glazing, both types are used extensively. Soft-coat is the preferred specification where maximum performance matters; hard-coat is the practical choice for most residential retrofits.
Solar Heat Gain Coefficient
SHGC measures how much solar radiation passes through the glass (heat from sunlight, not conduction). A lower SHGC means less heat gain from direct sun.
For Melbourne's north and west-facing windows, Low-E glass with a low SHGC (0.2–0.3) significantly reduces summer cooling load. South-facing windows benefit less from solar control but still gain from the improved U-value.
Is the Upgrade Worth It?
For most Melbourne homes, yes. The incremental cost over standard double glazing is typically $60–$120/m² for hard-coat Low-E — approximately $900–$1,800 for a whole-home retrofit.
The energy saving over a standard IGU is typically 15–25% of heating and cooling costs. At current Melbourne electricity prices, that is $300–$600 per year for a mid-size home. Payback on the Low-E upgrade alone: 2–6 years.
The Energy Efficient Windows page has full specification guidance. Use the Instant Estimate tool to compare standard vs Low-E pricing for your windows.
Related: Glass types guide — comparing all specifications
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