What Are Low-E Windows and Are They Worth It in Australia?
Low-emissivity (Low-E) windows use an invisible coating to reduce heat transfer in both directions — cutting cooling loads in summer and heating loads in winter.
Single-pane aluminium windows, common in Australian homes built before 1990, can account for up to 40% of heating and cooling energy loss. Low-E windows address this through a nearly invisible metallic coating applied to one pane of a double-glazed unit, which slows heat transfer without sacrificing natural light.
What Does Low-E Mean?
'Low-E' stands for low emissivity — a measure of how readily a surface radiates heat energy. Heat naturally moves from warmer areas to cooler ones. In winter, heat moves through your window from inside to outside. In summer, it moves from outside to inside. A Low-E coating slows this transfer in both directions.
How Low-E Windows Are Rated in Australia
In Australia, windows are rated through the Window Energy Rating Scheme (WERS), which uses stars (0–10) for both heating and cooling performance. The rating accounts for frame material, glazing type and gas fill. A higher heating star rating means less heat escapes in winter; a higher cooling star rating means less heat enters in summer. Different climate zones prioritise different ratings.
| Climate zone | Priority | What to look for |
|---|---|---|
| Zone 1–2 (Darwin, Brisbane) | Cooling | High cooling WERS star rating; Low solar heat gain coefficient (SHGC) |
| Zone 3–4 (Sydney, Adelaide, Perth) | Balanced | Good ratings for both heating and cooling |
| Zone 5–6 (Melbourne, southern SA) | Heating | High heating WERS star rating; Low-E with soft coating preferred |
| Zone 7–8 (ACT, alpine areas) | Heating dominant | High R-value frame; triple glazing may be justified |
Annual Savings Potential
Savings from Low-E window upgrades depend on how poor your existing windows are, your climate zone, energy prices and how much glass surface you have. Australian Department of Climate Change, Energy, the Environment and Water (DCCEEW) modelling suggests savings of $100–$500+ per year in southern states for a full window upgrade, with the top of that range in homes with extensive east- and west-facing single glazing.
Low-E Film vs Full Replacement
Low-E window film can be applied to existing single-pane windows as a cheaper alternative to full replacement. It provides some benefit — particularly for solar heat gain reduction in summer — but performs significantly below a proper double-glazed Low-E unit. Film does not provide the insulating air gap between panes that drives most of the efficiency gain.
Window upgrades are expensive. Prioritise: zone 5–7 homes with single-pane south-facing windows lose the most heat and benefit most from Low-E upgrades. In northern Australia, external shading (eaves, awnings) often delivers better value per dollar than glazing upgrades.
Simpler Alternatives First
- Quality heavy curtains or cellular blinds reduce heat transfer significantly at low cost
- External awnings and shutters block solar heat gain before it enters the glass
- Draught sealing around existing frames eliminates air leaks without window replacement
- These should be done before committing to full window replacement